INTRODUCTION
At present, aircraft gas turbine engines that have exhausted their flight life are used to drive gas pumping units, electric generators, gas jet installations, devices for cleaning quarries, snow blowers, etc. However, the alarming state of the domestic energy sector requires the use of aircraft engines and the attraction of the production potential of the aviation industry, primarily for the development of industrial energy.
The massive use of aircraft engines that have expired their flight life and retained the ability for further use allows the commonwealth of independent states to solve the problem, since in the context of a general decline in production, the preservation of labor embodied in engines and the saving of expensive materials used in their creation allows not only to slow down further economic downturn, but also achieve economic growth.
Experience in creating drive gas turbine plants based on aircraft engines, such as, for example, HK-12CT, HK-16CT, and then NK-36ST, NK-37, NK-38ST, AL-31ST, GTU-12P, -16P, -25P , confirmed the above.
It is extremely profitable to create urban-type power plants on the basis of aircraft engines. The area allotted for the station is not comparable less than for the construction of a thermal power plant, while at the same time the best environmental characteristics. At the same time, capital investments in the construction of power plants can be reduced by 30 ... 35%, as well as 2 ... 3 times reduced the volume of construction and installation work of power units (shops) and 20 ... 25% reduced construction time compared with workshops using stationary gas turbine drives. A good example is the Bezymyanskaya CHPP (Samara) with an energy capacity of 25 MW and a heat capacity of 39 Gcal / h, which for the first time included the NK-37 aircraft gas turbine engine.
There are several other important considerations in favor of converting aircraft engines. One of them is associated with the peculiarity of the distribution of natural resources on the territory of the CIS. It is known that the main reserves of oil and gas are located in the eastern regions of Western and Eastern Siberia, while the main consumers of energy are concentrated in the European part of the country and in the Urals (where most of the production assets and population are located). Under these conditions, the maintenance of the economy as a whole is determined by the possibility of organizing the transport of energy carriers from east to west with cheap, transportable power plants of optimal power with a high level of automation, capable of providing operation in a deserted version “under lock and key”.
The task of providing highways with the necessary number of drive units that meet these requirements is most rationally solved by extending the life (conversion) of large batches of aircraft engines removed from the wing after they have exhausted their flight resource Development of new areas devoid of roads and airfields requires the use of power plants of low weight and transported by existing ones. means (by water or by helicopters), while obtaining the maximum specific power (kW / kg) is also provided by the converted aircraft engine. Note that this indicator for aircraft engines is 5 ... 7 times higher than that of stationary installations. In this regard, let us point out one more advantage of an aircraft engine - a short time to reach the rated power (calculated in seconds), which makes it indispensable in emergency situations at nuclear power plants, where aircraft engines are used as backup units. Obviously, power plants created on the basis of aircraft engines can be used both as peak power plants and as standby units for a special period.
So, the geographical features of the location of energy carriers, the presence of a large (estimated in hundreds) number of aircraft engines removed from the wing annually and the growth of the required number of drives for various sectors of the national economy require the predominant increase in the fleet of drives based on aircraft engines. At present, the share of the aircraft drive in the total balance of capacities at compressor stations exceeds 33%. Chapter 1 of the book describes the features of the operation of aviation gas turbine engines as drives for blowers of gas pumping stations and electric generators, sets out the requirements and basic principles of rotation, examples of completed drive designs are given and trends in the development of converted aircraft engines are shown.
Chapter 2 discusses the problems and directions of increasing the efficiency and power of drives of power plants created on the basis of aircraft engines, the introduction of additional elements into the drive circuit and various methods of heat recovery. up to 48 ... 52%) and a service life of at least (30 ... 60) 103 hours.
The agenda includes the issue of increasing the service life of the drive to tr = (100 ... 120) -103 hours and reducing emissions of harmful substances. In this case, it becomes necessary to carry out additional measures up to alteration of units while maintaining the level and ideology of aircraft engine design. Drives with such modifications are intended only for ground use, since their mass (weight) characteristics are worse than those of the original aviation GTEs.
In some cases, despite the increase in the initial costs associated with changes in the engine design, the life cycle cost of such gas turbines is lower. Such improvements in GTU are all the more justified, since the exhaustion of the number of engines on the wing occurs faster than the exhaustion of the resource of installations operated on gas pipelines or as part of power plants.
In general, the book reflects the ideas that were introduced by the General Designer of Aerospace Technology, Academician of the USSR Academy of Sciences and the Russian Academy of Sciences
N. D. Kuznetsov into the theory and practice of converting aircraft engines, begun in 1957.
In preparing the book, in addition to domestic materials, the works of foreign scientists and designers published in scientific and technical journals were used.
The authors express their gratitude to the employees of JSC SNTK im. N. D. Kuznetsov "V.M. Danilchenko, O. V. Nazarov, O.P. Pavlova, D.I. Kustov, L.P. Zholobova, E.I. Senina for help in preparing the manuscript.
- Name: Conversion of aircraft gas turbine engines to ground-based gas turbines
- E.A. Gritsenko; B.P. Danilchenko; S.V. Lukachev; V.E. Reznik; Yu.I. Tsybizov
- Publisher: Samara Scientific Center of the Russian Academy of Sciences
- Year: 2004
- Pages: 271
- UDC 621.6.05
- Format:.pdf
- The size: 9.0 Mb
- Quality: excellent
- Series or Issue:-----
FREE DOWNLOAD Convert aviation
GTE in a ground-based GTU
Attention! You do not have permission to view hidden text.
Add to Favorites to Favorites from Favorites 0
Interesting vintage article that I think will interest colleagues.
ITS ADVANTAGES
The plane roars in the transparent blue of the sky. People stop, covering their eyes from the sun with their palms, looking for it between the rare islands of clouds. But they cannot find it. Maybe a cloud is hiding it, or has it flown so high that it is already invisible to the naked eye? No, someone has already seen him and shows his neighbor with his hand - not at all in the direction where the others are looking. Slim, with wings thrown back, like an arrow, it flies so fast that the sound of its flight reaches the ground from a point where the plane has long been gone. Sound seems to lag behind him. And the plane, as if frolicking in its native element, suddenly abruptly, almost vertically, takes off upward, overturns, falls down like a stone and again swiftly sweeps horizontally ... This is a jet plane.
The main component of the jet engine, which gives the aircraft this extremely high speed, almost equal to the speed of sound, is the gas turbine. In the last 10-15 years, she got on the plane, and the speed of artificial birds increased by four to five hundred kilometers. The best piston engines could not provide such speeds for production aircraft. How does this amazing engine, which provided aviation with such a big step forward, this newest engine - a gas turbine, work?
And then it suddenly turns out that the gas turbine is by no means the latest engine... It turns out that even in the last century there were projects for gas turbine engines. But until some time, determined by the level of technological development, a gas turbine could not compete with other types of engines. This is despite the fact that the gas turbine has a number of advantages over them.
Let us compare a gas turbine, for example, with a steam engine. The simplicity of its structure in this comparison immediately catches the eye. A gas turbine does not require an elaborate, bulky steam boiler, a huge condenser, and many other auxiliary mechanisms.
But even a conventional piston internal combustion engine does not have a boiler or a condenser. What are the advantages of a gas turbine over a piston engine, which it so rapidly ousted from high-speed aircraft?
The fact that a gas turbine engine is extremely light engine... Its weight per unit of power is significantly lower than that of other types of engines.
In addition, it does not have translationally moving parts - pistons, connecting rods, etc., which limit the engine speed. This advantage, which does not seem so important to people who are not particularly close to technology, often turns out to be decisive for the engineer.
The gas turbine has another overwhelming advantage over other internal combustion engines. It can run on solid fuels. Moreover, its efficiency will be not less, but more than that of the best piston internal combustion engine running on expensive liquid fuel.
What kind of efficiency can a gas turbine provide?
It turns out that already the simplest gas turbine plant, which can operate on gas with a temperature in front of the turbine of 1250-1300 ° C, will have an efficiency of about 40-45%. If you complicate the installation, use regenerators (they use the heat of the exhaust gas to heat the air), use intercooling and multi-stage combustion, you can get the efficiency of the gas turbine plant of the order of 55-60%. These figures show that a gas turbine can far surpass all existing engine types in terms of economy. Therefore, the victory of the gas turbine in aviation should be regarded only as the first victory of this engine, followed by others: in railway transport - over a steam engine, in stationary power engineering - over a steam turbine. The gas turbine should be considered the main engine of the near future.
ITS DISADVANTAGES
The basic structure of an aviation gas turbine today is not complicated (see diagram below). A compressor is located on the same shaft as the gas turbine, which compresses the air and directs it into the combustion chambers. From here, the gas enters the turbine blades, where part of its energy is converted into mechanical work necessary for the rotation of the compressor and auxiliary devices, primarily the pump for continuous supply of fuel to the combustion chambers. Another part of the gas energy is converted already in the jet nozzle, creating jet thrust... Sometimes turbines are made that generate more power than is required to drive the compressor and drive auxiliary devices; the excess part of this energy is transferred through the gearbox to the propeller. There are aircraft gas turbine engines equipped with both a propeller and a jet nozzle.
A stationary gas turbine does not fundamentally differ from an aviation one, only instead of a propeller, the rotor of an electric generator is attached to its shaft and the combustion gases are not emitted into the jet nozzle, but to the maximum possible limit they give the energy contained in them to the turbine blades. In addition, a stationary gas turbine, which is not bound by strict requirements for dimensions and weight, has a number of additional devices that increase its efficiency and reduce losses.
The gas turbine is a high-performance machine. We have already named the desired temperature of gases in front of the blades of its impeller - 1250-1300 °. This is the melting point of steel. Gas is moving at a speed of several hundred meters per second, heated to such a temperature in the nozzles and blades of the turbine. Its rotor makes over a thousand revolutions per minute. A gas turbine is a deliberately orchestrated flow of incandescent gas. The paths of the fiery streams moving in the nozzles and between the turbine blades are precisely predetermined and calculated by the designers.
The gas turbine is a high precision machine. The bearings of a shaft that makes thousands of revolutions per minute must be made to the highest accuracy class. Not the slightest imbalance can be tolerated in the rotor rotating at this speed, otherwise the beats will blow the machine apart. The requirements for the metal of the blades must be extremely high - centrifugal forces strain it to the limit.
These features of the gas turbine partially slowed down its implementation, despite all its high advantages. Indeed, what kind of heat-resistant and heat-resistant materials should be in order to withstand the most strenuous work for a long time at the melting temperature of steel? Modern technology does not know such materials.
The rise in temperature due to advances in metallurgy is very slow. Over the past 10-12 years, they have provided an increase in temperature by 100-150 °, that is, 10-12 ° per year. Thus, today our stationary gas turbines could operate (if there were no other ways to deal with high temperatures) at only about 700 ° C. The high efficiency of stationary gas turbines can be ensured only at a higher temperature of the working gases. If metallurgists increase the heat resistance of materials at the same rate (which is generally doubtful), only in fifty years will they ensure the operation of stationary gas turbines.
Engineers today are taking a different path. It is necessary to cool, they say, the elements of the gas turbine, which are washed by hot gases. This primarily applies to the nozzles and blades of the gas turbine impeller. And for this purpose, a number of various solutions have been proposed.
So, it is proposed to make the blades hollow and cool them from the inside either with cold air or liquid. There is another suggestion - to blow cold air around the blade surface, creating a protective cold film around it, as if putting the blade into a jacket made of cold air. Finally, you can make a blade of a porous material and through these pores from the inside supply a coolant, so that the blade "sweats", as it were. But all these proposals are very complicated in the case of a direct constructive solution.
There is one more unsolved technical problem in the design of gas turbines. After all, one of the main advantages of a gas turbine is that it can run on solid fuel. In this case, it is most expedient to burn the atomized solid fuel directly in the combustion chamber of the turbine. But it turns out that we do not know how to effectively separate the solid particles of ash and slag from the combustion gases. These particles with a size of more than 10-15 microns, together with a stream of incandescent gases, fall on the turbine blades and scratch and destroy their surface. Radical cleaning of combustion gases from ash and slag particles or combustion of atomized fuel so that solid particles are only less than 10 microns are formed - this is another task that must be solved in order for a gas turbine to "descend from heaven to earth".
IN AVIATION
What about aviation? Why is the efficiency of a gas turbine high in the sky at the same temperatures of gases more than on the ground? Because the main criterion for the efficiency of its operation is actually not the temperature of the combustion gases, but the ratio of this temperature to the outside air temperature. And at the heights mastered by our modern aviation, these temperatures are always relatively low.
Thanks to this, the gas turbine in aviation has become the main type of engine at the present time. Now high-speed aircraft have abandoned the piston engine. Long-range aircraft use a gas turbine in the form of an air-jet gas turbine or turboprop engine. In aviation, the advantages of the gas turbine over other engines in terms of size and weight were especially pronounced.
And these advantages, expressed in the exact language of numbers, are approximately as follows: a piston engine near the ground has a weight of 0.4-0.5 kg per 1 hp, a gas turbine engine - 0.08-0.1 kg per 1 hp. In high-altitude conditions, say at an altitude of 10 km, the piston engine becomes ten times heavier than a gas turbine air-jet engine.
Currently, the official world speed record for a turbojet aircraft is 1212 km / h. Airplanes are also designed for speeds much higher than the speed of sound (recall that the speed of sound at the ground is approximately 1220 km / h).
Even from what has been said, it is clear what a revolutionary engine the gas turbine is in aviation. History has never known a case when in such a short period of time (10-15 years) a new type of engine completely supplanted another, perfect type of engine in the whole field of technology.
BY LOCOMOTIVE
From the very appearance of railways until the end of the last century, a steam engine - a steam locomotive - was the only type of railway engine. At the beginning of our century, a new, more economical and perfect locomotive appeared - an electric locomotive. About thirty years ago, other new types of locomotives appeared on the railways - diesel locomotives and steam turbine locomotives.
Of course, the steam locomotive has undergone many significant changes during its existence. Its design also changed, and the main parameters - speed, weight, power - also changed. The traction and heat engineering characteristics of steam locomotives were constantly improving, which was facilitated by the introduction of an increased temperature of superheated steam, heating of feed water, heating of air supplied to the furnace, the use of pulverized coal heating, etc. However, the efficiency of steam locomotives is still very low and reaches only 6- eight%.
It is known that railway transport, mainly steam locomotives, consumes about 30-35 ° / about all coal mined in the country. Increasing the efficiency of steam locomotives by just a few percent would mean huge savings, amounting to tens of millions of tons of coal, mined from the ground by the hard work of miners.
Low efficiency is the main and most significant drawback of a steam locomotive, but not the only one. As you know, a steam engine is used as an engine on a steam locomotive, one of the main components of which is a connecting rod-crank mechanism. This mechanism is a source of harmful and dangerous forces acting on the railway track, which sharply limits the power of steam locomotives.
It should also be noted that the steam engine is not well suited to work with high steam parameters. After all, lubrication of the cylinder of a steam engine is usually carried out by splashing oil into fresh steam, and the oil has a relatively low temperature resistance.
What can be obtained if a gas turbine is used as a locomotive engine?
As a traction engine, a gas turbine has a number of advantages over reciprocating machines - steam and internal combustion. The gas turbine does not require water supply and water cooling, and consumes very little lubricant. The gas turbine successfully runs on low-grade liquid fuel and can run on solid fuel - coal. Solid fuel in a gas turbine can be combusted, firstly, in the form of gas after it has been previously gasified in so-called gas generators. Solid fuel can be burned in the form of dust and directly in the combustion chamber.
Only one development of the combustion of solid fuel in gas turbines without a significant increase in the gas temperature and even without the installation of heat exchangers will make it possible to build a gas turbine locomotive with an operating efficiency of about 13-15% instead of the efficiency of the best steam locomotives of 6-8%.
We will get a huge economic effect: firstly, a gas turbine locomotive will be able to use any fuel, including small fines (a conventional steam locomotive works much worse for small fines, since entrainment into the pipe in this case can reach 30-40%), and secondly, and most importantly, fuel consumption will be reduced by 2-2.5 times, which means that 15-18% of the total coal production in the Union, which is spent on steam locomotives, will be released from 30-35%. As can be seen from the above figures, the replacement of steam locomotives with gas turbine locomotives will give a colossal economic effect.
AT POWER PLANTS
Large district thermal power plants are the second most important consumer of coal. They consume about 18-20% of the total amount of coal mined in our country. At modern regional power plants, only steam turbines operate as an engine, the power of which in one unit reaches 150 thousand kW.
In a stationary gas turbine plant, applying all possible methods of increasing the efficiency of its operation, it would be possible to obtain an efficiency of the order of 55-60%, that is, 1.5-1.6 times higher than that of the best steam turbine plants, so that from the point from the point of view of economy we have here again the superiority of the gas turbine.
There are many doubts about the possibility of creating gas turbines of large capacities of the order of 100-200 thousand kW, especially since at present the most powerful gas turbine has a capacity of only 27 thousand kW. The main difficulty in creating a large-capacity turbine arises in the design of the last stage of the turbine.
The actual gas turbine is in gas turbine plants as a single-stage (nozzle apparatus and one disk with rotor blades), and multi-stage - as if several sequentially connected separate stages. In the course of the gas flow in the turbine from the first stage to the last, the dimensions of the discs and the length of the rotor blades increase due to the increase in the specific volume of the gas and reach their maximum values at the last stage. However, according to the strength conditions, the lengths of the blades, which must withstand the stresses from centrifugal forces, cannot exceed completely certain values for a given number of turbine revolutions and a given material of the blades. This means that when designing the last stage
turbine dimensions should not exceed certain limit values. This is the main difficulty.
Calculations show that gas turbines of high and ultra-high power (about 100 thousand kW) can be constructed only under the condition of a sharp increase in the temperature of the gases in front of the turbine. Engineers have a kind of gas turbine power density ratio, calculated in kW per 1 sq. square meter of the last stage of the turbine. For installations with powerful steam turbines with an efficiency of about 35%, it is equal to 16.5 thousand kW per square meter. m. For gas turbines with a combustion gas temperature of 600 °, it is only 4 thousand per square meter. m. Accordingly, the efficiency of such gas turbine plants of the simplest scheme does not exceed 22%. It is necessary to raise the temperature of the cans at the turbine to 1150 °, as the specific power factor rises to 18 thousand kW per sq. m., and efficiency, respectively, up to 35%. For a more advanced gas turbine, operating with a gas temperature in the 1300s, it already rises to 42.5 thousand per square meter. m, and the efficiency, respectively, up to 53.5%!
BY CAR
As you know, the main engine of all cars is the internal combustion engine. However, over the past five to eight years, prototypes of both cargo and passenger cars with a gas turbine. This once again confirms that the gas turbine will be the engine of the near future in many areas of the national economy.
What are the advantages of a gas turbine as car engine?
The first is the lack of a gearbox. The twin-shaft gas turbine has excellent traction characteristics, developing maximum effort when starting off. As a result, we get a great throttle response of the car.
An automobile turbine runs on cheap fuel and has small dimensions. But since an automobile gas turbine is still a very young type of engine, designers who are trying to create an engine that compete with a piston constantly face many issues that need to be addressed.
A major drawback of all existing automobile gas turbines in comparison with reciprocating internal combustion engines is their low efficiency. Cars require engines of comparatively low power, even a 25 ton truck has an engine of approximately 300 hp. sec., and this power is very small for a gas turbine. For such a power, the turbine turns out to be very small, as a result of which the efficiency of the installation will be low (12-15%), moreover, it drops sharply with decreasing load.
To judge the dimensions that a gas turbine of a car can have, we present the following data: the volume occupied by such a gas turbine is approximately ten times less than the volume of a piston engine of the same power. The turbine has to be made with a high number of revolutions (about 30-40 thousand rpm), and in some cases even higher (up to 50 thousand rpm). So far, such high speeds are hard to master.
Thus, low efficiency and design difficulties caused by high turnover and the small size of the gas turbine are the main brake on the installation of the gas turbine on the car.
The present time period is a birth period for an automobile gas turbine, but the time is not far off when a highly economical low-power gas turbine unit will be created. Huge prospects will open up for an automobile gas turbine operating on solid fuel, since motor transport is one of the most capacious consumers of liquid fuel, and the conversion of motor transport to coal will give a huge national economic effect.
We briefly got acquainted with those areas of the national economy where the gas turbine as an engine has already taken or may soon take its rightful place. There are a number of other industries in which the gas turbine has such advantages over other engines that its use is certainly advantageous. So, for example, there are all the possibilities of widespread use of a gas turbine on ships, where its small dimensions and weight are of great importance.
Soviet scientists and engineers are confidently working on improving gas turbines and eliminating structural difficulties that prevent their widespread use. These difficulties will undoubtedly be eliminated, and then the decisive introduction of the gas turbine in railway transport and in stationary energy will begin.
A little time will pass, and the gas turbine will cease to be the engine of the future, but will become the main engine in various sectors of the national economy.
THE IDEA to use gas turbine engines in automobiles has arisen long ago. But only in the last few years has their design reached the level of perfection that gives them the right to exist.
The high level of development of the theory of blade engines, metallurgy and production technology now provides a real opportunity to create reliable gas turbine engines that can successfully replace piston internal combustion engines on a car.
What is a gas turbine engine?
In fig. a schematic diagram of such an engine is shown. A rotary compressor, located on the same shaft as the gas turbine, draws in air from the atmosphere, compresses it and pumps it into the combustion chamber. The fuel pump, also driven by the turbine shaft, pumps fuel into an injector located in the combustion chamber. The gaseous products of combustion enter through the guide vane onto the rotor blades of the gas turbine wheel and force it to rotate in one definite direction. The exhaust gases in the turbine are discharged into the atmosphere through a branch pipe. The gas turbine shaft rotates in bearings.
Compared with reciprocating internal combustion engines, the gas turbine engine has very significant advantages. True, he, too, is not yet free of shortcomings, but they are gradually eliminated as the design develops.
When characterizing a gas turbine, first of all, it should be noted that, like a steam turbine, it can develop high speeds. This makes it possible to obtain significant power from much smaller (compared to piston) and almost 10 times lighter in weight engines.
The rotary motion of the shaft is essentially the only kind of motion in a gas turbine, while in an internal combustion engine, in addition to rotational motion crankshaft, there is a reciprocating movement of the piston, as well as a complex movement of the connecting rod. Gas turbine engines do not require special cooling devices. The absence of rubbing parts with a minimum number of bearings ensures long-term performance and high reliability of the gas turbine engine.
To power the gas turbine engine, kerosene or diesel fuel is used.
The main reason that hinders the development of automotive gas turbine engines is the need to artificially limit the temperature of the gases entering the turbine blades. This reduces the efficiency of the engine and leads to an increased specific fuel consumption (by 1 hp). The gas temperature has to be limited for gas turbine engines of passenger and trucks within 600-700 ° С, and in aircraft turbines up to 800-900 ° С because high heat-resistant alloys are still very expensive.
Currently, there are already some ways to increase the efficiency of gas turbine engines by cooling the blades, using the heat of exhaust gases to heat the air entering the combustion chambers, producing gases in highly efficient free-piston generators operating on a diesel-compressor cycle with a high compression ratio and etc. The solution to the problem of creating a highly efficient automobile gas turbine engine largely depends on the success of work in this area.
Schematic diagram of a two-shaft gas turbine engine with a heat exchanger
Most of the existing automobile gas turbine engines are built according to the so-called two-shaft scheme with heat exchangers. Here, a special turbine 8 serves to drive the compressor 1, and a traction turbine 7 serves to drive the wheels of the car. The shafts of the turbines are not interconnected. Gases from the combustion chamber 2 are first supplied to the turbine blades of the compressor drive, and then to the blades of the traction turbine. The air forced by the compressor, before entering the combustion chambers, is heated in heat exchangers 3 due to the heat given off by the exhaust gases. The use of a two-shaft scheme creates an advantageous traction characteristic of gas turbine engines, which makes it possible to reduce the number of stages in a conventional car gearbox and improve its dynamic qualities.
Due to the fact that the traction turbine shaft is not mechanically connected to the compressor turbine shaft, its speed can vary depending on the load without significantly affecting the compressor shaft speed. As a result, the characteristic of the torque of the gas turbine engine has the form shown in Fig., Where the characteristic of the piston automobile engine is also plotted for comparison (dotted line).
It can be seen from the diagram that in a piston engine, as the number of revolutions decreases, which occurs under the influence of an increasing load, the torque initially increases slightly and then decreases. At the same time, in a twin-shaft gas turbine engine, the torque automatically increases as the load increases. As a result, the need to shift the gearbox is eliminated or occurs much later than with a piston engine. On the other hand, acceleration during acceleration in a two-shaft gas turbine engine will be much greater.
The characteristic of a single-shaft gas turbine engine differs from that shown in Fig. and, as a rule, inferior, in terms of the requirements of the dynamics of the car, the characteristics of the piston engine (with equal power).
The gas turbine engine has great prospects. In this engine, gas for the turbine is generated in a so-called free piston generator, which is a two-stroke diesel engine and a piston compressor combined in a common unit. The energy from the diesel pistons is transferred directly to the compressor pistons. Due to the fact that the movement of piston groups is carried out exclusively under the influence of gas pressure and the mode of movement depends only on the course of thermodynamic processes in diesel and compressor cylinders, such a unit is called a free piston unit. In its middle part there is a cylinder 4, open on both sides, having a direct-flow slot blowing, in which a two-stroke working process with compression ignition takes place. In the cylinder, two pistons move oppositely, one of which 9 opens during the working stroke and closes the exhaust ports cut in the cylinder walls during the return stroke. Another piston 3 also opens and closes the purge ports. The pistons are connected to each other by a light rack or pinion synchronization mechanism, not shown in the diagram. When they get closer, the air trapped between them is compressed; by the time the dead center is reached, the temperature of the compressed air becomes sufficient to ignite the fuel, which is injected through the nozzle 5. As a result of the combustion of the fuel, gases with high temperature and pressure are formed; they force the pistons to spread apart, while the piston 9 opens the exhaust ports through which the gases rush into the gas collector 7. Then the purge ports open through which compressed air enters the cylinder 4, displaces the exhaust gases from the cylinder, mixes with them and also enters the gas collector. While the purge ports remain open, compressed air has time to clear the cylinder from exhaust gases and fill it, thus preparing the engine for the next working stroke.
Compressor pistons 2 are connected to pistons 3 and 9 and move in their cylinders. With the diverging stroke of the pistons, air is sucked from the atmosphere into the compressor cylinders, while the self-acting inlet valves 10 are open, and the outlet 11 are closed. With the opposite stroke of the pistons, the intake valves are closed, and the exhaust valves are open, and through them air is pumped into the receiver 6, which surrounds the diesel cylinder. The pistons move towards each other due to the air energy accumulated in the buffer cavities 1 during the previous working stroke. Gases from the collector 7 enter the traction turbine 8, the shaft of which is connected to the transmission. The following comparison of the efficiency factors shows that the described gas turbine engine is already as effective as internal combustion engines in terms of its efficiency:
Diesel 0.26-0.35
Gasoline engine 0.22-0.26
Gas turbine with constant volume combustion chambers without heat exchanger 0.12-0.18
Gas turbine with constant volume combustion chambers with heat exchanger 0.15-0.25
Gas turbine with free piston gas generator 0.25-0.35
Thus, the efficiency of the best samples of turbines is not inferior to the efficiency of diesel engines. It is no coincidence that the number of experimental gas turbine vehicles of various types is increasing every year. All new firms in various countries are announcing their work in this area.
This two-chamber engine, without heat exchanger, has an effective output of 370 hp. with. Kerosene serves as fuel for it. The compressor shaft rotation speed reaches 26,000 rpm, and the traction turbine shaft rotation speed ranges from 0 to 13,000 rpm. The temperature of the gases entering the turbine blades is 815 ° C, the air pressure at the compressor outlet is 3.5 atm. Total weight power plant designed for a racing car is 351 kg, with the gas-producing part weighing 154 kg, and the traction part with a gearbox and transmission to the drive wheels - 197 kg.
Ph.D. A.V. Ovsyannik, head. Department of Industrial Heat Power Engineering and Ecology;
Ph.D. A.V. Shapovalov, associate professor;
V.V. Bolotin, engineer;
Gomel State Technical University named after P.O. Sukhoi ", Republic of Belarus
The article provides a rationale for the possibility of creating a CHPP on the basis of a converted AGTD as part of a gas turbine plant (GTU), an assessment of the economic effect of introducing AGTD into the power industry as part of large and medium-sized CHPPs to repay peak electrical loads.
Aviation Gas Turbine Overview
One of the successful examples of the use of AGTD in the power industry is the cogeneration GTU 25/39, installed and in commercial operation at the Bezymyanskaya CHPP located in the Samara region in Russia, which is described below. The gas turbine unit is designed to generate electricity and heat for the needs of industrial enterprises and household consumers. The electric power of the plant is 25 MW, and the heat capacity is 39 MW. The total capacity of the installation is 64 MW. The annual productivity of electricity is 161.574 GWh / year, thermal energy is 244120 Gcal / year.
The unit is distinguished by the use of a unique aircraft engine NK-37, providing an efficiency of 36.4%. This efficiency provides a high plant efficiency unattainable in conventional thermal power plants, as well as a number of other advantages. The unit operates on natural gas with a pressure of 4.6 MPa and a flow rate of 1.45 kg / s. In addition to electricity, the unit produces 40 t / h of steam with a pressure of 14 kgf / cm 2 and heats up 100 t of heating water from 70 to 120 ° C, which makes it possible to provide light and heat to a small town.
When the unit is located on the territory of thermal power plants, no additional special units for chemical water treatment, water discharge, etc. are required.
Such gas turbine power plants are indispensable for use in cases where:
■ a comprehensive solution to the problem of supplying electric and thermal energy to a small town, industrial or residential area is required - the modularity of the installations makes it easy to assemble any option depending on the needs of the consumer;
■ industrial development of new areas of human life is being carried out, including those with living conditions, when the compactness and manufacturability of the installation is especially important. Normal operation of the installation is ensured in the ambient temperature range from -50 to +45 ° C under the influence of all other unfavorable factors: humidity up to 100%, precipitation in the form of rain, snow, etc .;
■ the efficiency of the installation is important: high efficiency ensures the possibility of producing cheaper electric and heat energy and a short payback period (about 3.5 years) with capital investments in the construction of the installation of 10 million 650 thousand dollars. USA (according to the manufacturer).
In addition, the installation is distinguished by its environmental friendliness, the presence of multi-stage noise suppression, and full automation of control processes.
GTU 25/39 is a stationary unit of block-container type with a size of 21 m by 27 m. water cooling tower and free-standing gas booster compressor. In the absence of the need for water and steam, the design of the installation is greatly simplified and cheaper.
The installation itself includes an NK-37 aircraft engine, a TKU-6 waste heat boiler and a turbine generator.
The total installation time is 14 months.
In Russia, a large number of units based on converted AGTDs with a capacity from 1000 kW to several tens of MW are produced, they are in demand. This confirms the economic efficiency of their use and the need for further developments in this area of the industry.
Installations manufactured at CIS plants differ:
■ low specific capital investments;
■ block execution;
■ shortened installation time;
■ short payback period;
■ the possibility of full automation, etc.
Characteristics of a gas turbine unit based on the converted AI-20 engine
A very popular and most frequently used gas turbine unit based on the AI-20 engine. Consider a gas turbine CHPP (GTTPP), in relation to which studies were carried out and calculations of the main indicators were performed.
The GTTETs-7500 / 6.3 gas turbine combined heat and power plant with an installed electric power of 7500 kW consists of three gas turbine generators with AI-20 turboprop engines with a rated electric power of 2500 kW each.
Thermal power of the GTHPP is 15.7 MW (13.53 Gcal / h). Behind each gas turbine generator there is a gas heater for network water (GWSW) with finned pipes for heating water with exhaust gases for heating, ventilation and hot water supply of the settlement. The exhaust gases in the aircraft engine pass through each economizer in an amount of 18.16 kg / s with a temperature of 388.7 ° C at the inlet to the economizer. In the GPSV, the gases are cooled to a temperature of 116.6 о С and fed into the chimney.
For modes with reduced heat loads, bypassing of the exhaust gas flow with output to the chimney is introduced. Water consumption through one economizer is 75 t / h. Mains water is heated from a temperature of 60 to 120 ° C and is supplied to consumers for heating, ventilation and hot water supply under a pressure of 2.5 MPa.
Technical indicators of a GTU based on the AI-20 engine: power - 2.5 MW; the degree of pressure increase - 7.2; the temperature of the gases in the turbine at the inlet - 750 о С, at the outlet - 388.69 о С; gas consumption - 18.21 kg / s; number of shafts - 1; air temperature in front of the compressor - 15 ° C. Based on the available data, we calculate the output characteristics of the gas turbine unit according to the algorithm given in the source.
Output characteristics of a GTU based on the AI-20 engine:
■ specific useful work of the gas turbine unit (at η fur = 0.98): H e = 139.27 kJ / kg;
■ efficiency factor: φ = 3536;
■ air consumption at power N gtu = 2.5 MW: G k = 17.95 kg / s;
■ fuel consumption at power N gtu = 2.5 MW: G top = 0.21 kg / s;
■ total consumption of exhaust gases: g g = 18.16 kg / s;
■ specific air consumption in the turbine: g k = 0.00718 kg / kW;
■ specific heat consumption in the combustion chamber: q 1 = 551.07 kJ / kg;
■ effective efficiency of the gas turbine unit: η е = 0.2527;
■ specific consumption of equivalent fuel for generated electricity (at generator efficiency η gen = 0.95) without utilization of exhaust gas heat: b у. t = 511.81 g / kWh.
Based on the data obtained and in accordance with the calculation algorithm, you can proceed to obtaining technical and economic indicators. Additionally, we set the following: the installed electric power of the GTHPP - N set = 7500 kW, the nominal thermal power of the GTHPP installed at the GTHPP - Qtp = 15736.23 kW, the electricity consumption for auxiliary needs is assumed to be 5.5%. As a result of the studies and calculations, the following values were determined:
■ gross primary energy coefficient of the GTHPP, equal to the ratio of the sum of the electric and thermal capacities of the GTHPP to the product of the specific fuel consumption with the lowest calorific value of the fuel, η b GTPP = 0.763;
■ net primary energy coefficient of GTTPP η n GTTPP = 0.732;
■ production efficiency electrical energy in a cogeneration gas turbine unit, equal to the ratio of the specific work of gas in the gas turbine unit to the difference in the specific heat consumption in the combustion chamber of the gas turbine unit per 1 kg of the working fluid and the specific heat removal in the gas turbine unit from 1 kg of exhaust gases of the gas turbine unit, η e gtu = 0.5311.
Based on the available data, it is possible to determine the technical and economic indicators of the GTHPP:
■ consumption of equivalent fuel for power generation in a cogeneration gas turbine unit: VGt U = 231.6 g of fuel equivalent / kWh;
■ hourly consumption of equivalent fuel for power generation: B e gtu = 579 kg of fuel equivalent / h;
■ hourly consumption of equivalent fuel in a gas turbine unit: B h ey gtu == 1246 kg of reference fuel. t / h
Heat generation in accordance with the "physical method" refers to the remaining amount of equivalent fuel: B t h = 667 kg of fuel equivalent. t / h
The specific consumption of equivalent fuel for the generation of 1 Gcal of heat in a cogeneration gas turbine unit will be: W t gtu = 147.89 kg of fuel equivalent / h.
Technical and economic indicators of mini-CHP are given in table. 1 (in the table and below, prices are given in Belarusian rubles, 1000 Belarusian rubles ~ 3.5 Russian rubles - Ed. Note).
Table 1. Technical and economic indicators of mini-CHPP based on the converted AGTD AI-20, sold at its own expense (prices are indicated in Belarusian rubles).
| The name of indicators | Units
measurements |
The quantity |
| Installed electrical power | MW | 3-2,5 |
| Installed thermal power | MW | 15,7 |
| Specific capital investments per unit of electrical power | RUB mln / kWh | 4 |
| Annual electricity supply | kWh | 42,525-10 6 |
| Annual heat supply | Gcal | 47357 |
| Unit cost: | ||
| - electricity | RUB / kWh | 371,9 |
| - thermal energy | RUB / G cal | 138700 |
| Balance sheet (gross) profit | RUB million | 19348 |
| Payback period | years | 6,3 |
| Break even | % | 34,94 |
| Profitability (overall) | % | 27,64 |
| Internal rate of return | % | 50,54 |
Economic calculations show that the payback period for the combined production of electricity and heat with AGTD is up to 7 years when projects are implemented at their own expense. At the same time, the construction period can range from several weeks for the installation of small installations with an electric power of up to 5 MW, up to 1.5 years when commissioning an installation with an electric power of 25 MW and a heat one of 39 MW. The shortened installation time is explained by the modular delivery of power plants based on AGTD with full factory readiness.
Thus, the main advantages of the converted AGTDs, when introduced into the power industry, are as follows: low specific capital investments in such installations, a short payback period, reduced construction time due to the modularity of execution (the installation consists of assembly blocks), the possibility of complete automation of the station, etc.
For comparison, we will give examples of operating gas engine mini-CHPPs in the Republic of Belarus, their main technical and economic parameters are shown in table. 2.
Having made a comparison, it is easy to notice that, against the background of already operating installations, gas turbine installations based on converted aircraft engines have a number of advantages. Considering AGTP as highly maneuverable power plants, it is necessary to bear in mind the possibility of their significant overload by transferring them to a steam-gas mixture (due to the injection of water into the combustion chambers), while it is possible to achieve an almost threefold increase in the power of a gas turbine unit with a relatively small decrease in its efficiency.
The efficiency of these stations increases significantly when they are located at oil wells, using associated gas, at oil refineries, at agricultural enterprises, where they are as close as possible to consumers of thermal energy, which reduces energy losses during its transportation.
To cover acute peak loads, it is promising to use the simplest stationary aviation gas turbines... In a conventional gas turbine, the time to take on the load after starting is 15-17 minutes.
Gas turbine stations with aircraft engines are very maneuverable, require a short (415 min) time to start from a cold state to full load, can be fully automated and controlled remotely, which ensures their effective use as an emergency reserve. The duration of the start-up before taking the full load of the operating gas turbine units is 30-90 minutes.
The indicators of the maneuverability of the GTU based on the converted GTE AI-20 are presented in Table. 3.
Table 3. Maneuverability indicators of GTU based on the converted AI-20 GTE.
Conclusion
Based on the work carried out and the results of the study of gas turbine plants based on converted AGTDs, the following conclusions can be drawn:
1. An effective direction for the development of the thermal power industry in Belarus is the decentralization of energy supply with the use of converted AGTDs, and the most effective is the combined generation of heat and electricity.
2. The AGTD unit can operate both autonomously and as part of large industrial enterprises and large thermal power plants, as a reserve for accepting peak loads, has a short payback period and shortened installation times. There is no doubt that this technology has the prospect of development in our country.
Literature
1. Khusainov R.R. The work of CHP in the conditions of the wholesale electricity market // Energetik. - 2008. - No. 6. - S. 5-9.
2. Nazarov V.I. On the issue of calculating generalized indicators at CHPPs // Energetika. - 2007. - No. 6. - S. 65-68.
3. Uvarov V.V. Gas turbines and gas turbine installations - M .: Higher. shk., 1970 .-- 320 p.
4. Samsonov V.S. Economics of enterprises of the energy complex - M .: Vyssh. shk., 2003 .-- 416 p.
The "turbine" topic is as complex as it is vast. Therefore, of course, there is no need to talk about its full disclosure. Let's take, as always, "general acquaintance" and "separate interesting moments" ...
At the same time, the history of the aviation turbine is very short in comparison with the history of the turbine in general. This means that we cannot do without a certain theoretical and historical excursion, the content of which, for the most part, does not relate to aviation, but is the basis for a story about the use of a gas turbine in aircraft engines.
About the rumble and rumble ...
Let's start in a somewhat unconventional way and remember about "". This is a fairly common phrase that is usually used by inexperienced authors in the media when describing the work of powerful aircraft. Here you can also add "roar, whistle" and other loud definitions for all the same "aircraft turbines".
Quite familiar words for many. However, people who understand it well know that in fact all these "sound" epithets most often characterize the operation of jet engines as a whole or its parts, which have very little relation to turbines as such (except, of course, mutual influence during their joint work in the general turbojet engine cycle).
Moreover, in a turbojet engine (just such are the object of rave reviews), as a direct reaction engine that creates thrust by using the reaction of a gas stream, the turbine is only a part of it and has rather an indirect relationship to the "roaring roar".
And on those engines where, like a node, it plays, in some way, a dominant role (these are engines of an indirect reaction, and they are not called for nothing gas turbine), there is no longer such an impressive sound, or it is created by completely different parts of the power plant of the aircraft, for example, the propeller.
That is, neither a hum, nor a rumble, as such, to aircraft turbine don't really apply. However, despite such sound ineffectiveness, it is a complex and very important unit of a modern turbojet engine (GTE), which often determines its main performance characteristics... Not a single gas turbine engine can do without a turbine, by definition.
Therefore, the conversation, of course, is not about impressive sounds and the incorrect use of definitions of the Russian language, but about an interesting unit and its relationship to aviation, although this is far from the only area of its application. How technical device a turbine appeared long before the very concept of an "aircraft" (or airplane), and even more so a gas turbine engine for it.
History + some theory ...
And even a very long time. Since then, when mechanisms were invented that transform the energy of the forces of nature into useful action. The most simple in this regard and therefore one of the first to appear were the so-called rotary motors.
This definition itself, of course, only appeared in our days. However, its meaning is precisely what determines the simplicity of the engine. Natural energy directly, without any intermediate devices, is converted into mechanical power of the rotary motion of the main power element of such an engine - the shaft.
Turbine- a typical representative of a rotary engine. Looking ahead, we can say that, for example, in a piston internal combustion engine (ICE), the main element is the piston. It performs a reciprocating motion, and to obtain the rotation of the output shaft, you need to have an additional crank mechanism, which naturally complicates and makes the structure heavier. The turbine is much more profitable in this respect.
For a rotary internal combustion engine, as a heat engine, which, by the way, is a turbojet engine, the name "rotary" is usually used.
Water Mill Turbine Wheel
Some of the most famous and oldest uses of the turbine are large mechanical mills, used by man since time immemorial for various household needs (not only for grinding grain). These are referred to as aquatic and wind turbines mechanisms.
For a long period of ancient history (the first mentions from about the 2nd century BC) and the history of the Middle Ages, these were in fact the only mechanisms used by man for practical purposes. The possibility of their application, with all the primitiveness of the technical circumstances, was the simplicity of the transformation of the energy of the working fluid used (water, air).
A windmill is an example of a turbine wheel.
In these, in fact, real rotary motors, the energy of the water or air flow is converted into shaft power and, ultimately, useful work. This happens when the flow interacts with the working surfaces, which are water wheel blades or windmill wings... Both, in fact, are the prototype of modern blades paddle machines, which are currently used turbines (and compressors, by the way, too).
Another type of turbine is known, first documented (apparently invented) by the ancient Greek scientist, mechanic, mathematician and natural scientist Heron of Alexandria ( Heron ho Alexandreus,1 century AD) in his treatise "Pneumatics". The invention he described was named eolipil , which in translation from Greek means "ball of Eolus" (god of the wind, Αἴολος - Eolus (Greek), pila - ball (lat.)).
Eolipilus of Herona.
In it, the ball was equipped with two oppositely directed nozzle tubes. Steam escaped from the nozzles, entering the ball through pipes from the boiler located below and thereby forcing the ball to rotate. The action is clear from the figure below. It was a so-called inverted turbine rotating to the side opposite to the steam outlet. Turbines of this type have a special name - reactive (more details below).
It is interesting that Heron himself hardly imagined what was the working body in his car. In that era, steam was identified with air, even the name testifies to this, because Aeolus rules the wind, that is, the air.
Eolipil was, in general, a full-fledged heat engine, which converted the energy of the burned fuel into mechanical energy of rotation on the shaft. Perhaps it was one of the first heat engines in history. True, its usefulness was still "not complete", since the invention did not perform useful work.
Eolipil, among other mechanisms known at that time, was included in the set of the so-called "theater of automata", which was very popular in subsequent centuries, and was actually just an interesting toy with an incomprehensible future.
From the moment of its creation and in general from the era when people in their first mechanisms used only "clearly manifesting themselves" forces of nature (wind force or the force of gravity of falling water) to the beginning of the confident use of thermal energy of fuel in newly created heat engines, more than one hundred years.
The first such units were steam engines. The real working examples were not invented and built in England until the end of the 17th century and were used to pump water from coal mines. Later, steam engines with a piston mechanism appeared.
Later, with the development of technical knowledge, piston internal combustion engines of various designs, more advanced and more efficient mechanisms, entered the scene. They already used gas (combustion products) as a working fluid and did not require bulky steam boilers to heat it.
Turbines as the main units of heat engines, they also followed a similar path in their development. And although there are separate mentions of some copies in history, but noteworthy and also documented, including patented, aggregates appeared only in the second half of the 19th century.
It all started with steam ...
It was with the use of this working fluid that practically all the basic principles of a turbine (hereinafter also a gas turbine), as an important part of a heat engine, were worked out.
Jet turbine patented by Laval.
Developments of a talented Swedish engineer and inventor were quite characteristic in this regard. Gustave de Laval(Karl Gustaf Patrik de Laval). His research at that time was connected with the idea of developing a new milk separator with increased drive speeds, which significantly increased productivity.
To obtain a high rotational speed (revolutions) by using the then traditional (however, the only existing) piston steam engine was not possible due to the high inertia of the most important element - the piston. Realizing this, Laval decided to try to stop using the piston.
It is said that the very idea came to him while observing the operation of sandblasting machines. In 1883 he received his first patent (English patent No. 1622) in this area. The patented device was called " Steam and water turbine».
It was an S-shaped tube, at the ends of which converging nozzles were made. The tube was mounted on a hollow shaft through which steam was supplied to the nozzles. In principle, all this was no different from the eolipil of Heron of Alexandria.
The manufactured device worked reliably enough with high revolutions for the technology of that time - 42,000 rpm. The rotation speed reached 200 m / s. But with such good parameters turbine had extremely low efficiency. And attempts to increase it with the existing prior art have led nowhere. Why did it happen?
——————-
A little theory ... A little more details about the features ....
The aforementioned efficiency (for modern aircraft turbines this is the so-called power or effective efficiency) characterizes the efficiency of using the expended energy (available) to drive the turbine shaft. That is, how much of this energy was spent useful in rotating the shaft, and how much " flew into the pipe».
It flew out. For the described type of turbine, called reactive, this expression is just right. Such a device receives a rotary motion on the shaft under the action of the reaction force of the outgoing gas jet (or in this case steam).
A turbine, as a dynamic expansion machine, in contrast to volumetric (piston) machines, requires for its operation not only compression and heating of the working fluid (gas, steam), but also its acceleration. Here expansion (increase in specific volume) and pressure drop occurs due to acceleration, in particular in the nozzle. In a piston engine, this is due to an increase in the volume of the cylinder chamber.
As a result, that large potential energy of the working fluid, which was formed as a result of supplying the thermal energy of the burnt fuel to it, turns into kinetic energy (minus various losses, of course). And kinetic (in a jet turbine) by means of reaction forces - into mechanical work on the shaft.
And here is how fully kinetic energy goes into mechanical in this situation and the efficiency tells us. The higher it is, the less kinetic energy is possessed by the flow leaving the nozzle into the environment. This remaining energy is called " loss with output speed”, And it is directly proportional to the square of the outgoing flow rate (everyone probably remembers mС 2/2).
The principle of operation of a jet turbine.
Here we are talking about the so-called absolute speed C. After all, the outgoing stream, more precisely, each of its particles, participates in a complex motion: rectilinear plus rotational. Thus, the absolute speed C (relative to the stationary coordinate system) is equal to the sum of the turbine rotation speed U and the relative flow speed W (speed relative to the nozzle). The sum is of course vector, shown in the figure.
Segner's wheel.
The minimum losses (and maximum efficiency) correspond to the minimum speed C, ideally, it should be zero. And this is possible only if W and U are equal (seen from the figure). The peripheral speed (U) in this case is called optimal.
Such equality would not be difficult to ensure on hydraulic turbines (of the type Segner wheels), since the velocity of liquid outflow from the nozzles for them (similar to the velocity W) is relatively low.
But the same speed W for gas or vapor is much higher due to the large difference in density between liquid and gas. So, at a relatively low pressure of only 5 atm. a hydraulic turbine can give an outflow speed of only 31 m / s, and a steam turbine - 455 m / s. That is, it turns out that already at sufficiently low pressures (only 5 atm.), The Laval jet turbine should have had a peripheral speed above 450 m / s for reasons of high efficiency.
For the then level of technology development, this was simply impossible. It was impossible to make a reliable design with such parameters. It also made no sense to reduce the optimal peripheral speed by decreasing the relative (W), since this can only be done by reducing the temperature and pressure, and hence the overall efficiency.
Active Laval turbine ...
The Laval jet turbine did not lend itself to further improvement. Despite the attempts made, things have come to a standstill. Then the engineer took a different path. In 1889 he patented a different type of turbine, which was later named active. Abroad (in English) it is now called impulse turbine, that is, impulse.
The device claimed in the patent consisted of one or more stationary nozzles supplying steam to bucket-like blades mounted on the rim of a movable impeller (or disk).
Active single-stage steam turbine patented by Laval.
The working process in such a turbine is as follows. Steam accelerates in nozzles with an increase in kinetic energy and a drop in pressure and falls on the rotor blades, on their concave part. As a result of the impact on the impeller blades, it begins to rotate. Or you can also say that rotation occurs due to the impulsive action of the jet. Hence the English name impulseturbine.
At the same time, in the interscapular channels having an almost constant cross-section, the flow does not change its velocity (W) and pressure, but changes direction, that is, it turns at large angles (up to 180 °). That is, we have at the exit from the nozzle and at the entrance to the interscapular channel: absolute speed С 1, relative W 1, peripheral speed U.
At the output, respectively, C 2, W 2, and the same U. In this case, W 1 = W 2, C 2< С 1 – из-за того, что часть кинетической энергии входящего потока превращается в механическую на валу турбины (импульсное воздействие) и абсолютная скорость падает.
In principle, this process is shown in a simplified figure. Also, to simplify the explanation of the process, it is assumed here that the vectors of absolute and peripheral velocities are practically parallel, the flow changes direction in the impeller by 180 °.
Steam (gas) flow in an active turbine stage.
If we consider the speeds in absolute terms, then it can be seen that W 1 = C 1 - U, and C 2 = W 2 - U. Thus, based on the foregoing, for the optimal mode, when the efficiency takes maximum values, and losses from the output speed tend to a minimum (that is, C 2 = 0) we have C 1 = 2U or U = C 1/2.
We get that for an active turbine optimum peripheral speed is half the velocity of the outflow from the nozzle, that is, such a turbine is half as much less loaded than a jet turbine, and the task of obtaining a higher efficiency is facilitated.
Therefore, in the future, Laval continued to develop just this type of turbine. However, despite the decrease in the required peripheral speed, it still remained high enough, which entailed equally large centrifugal and vibration loads.
The principle of operation of an active turbine.
The consequence of this was structural and strength problems, as well as problems of eliminating the imbalance, which are often solved with great difficulty. In addition, there were other unresolved and unsolvable factors in the then conditions, which ultimately reduced the efficiency of this turbine.
These included, for example, the imperfection of the aerodynamics of the blades, causing increased hydraulic losses, as well as the pulsating effect of individual jets of steam. In fact, only a few or even one blade could be active blades perceiving the action of these jets (or jets) at a time. At the same time, the rest moved idle, creating additional resistance (in a steam atmosphere).
Such turbines there was no opportunity to increase power due to an increase in temperature and steam pressure, since this would lead to an increase in peripheral speed, which was absolutely unacceptable due to all the same design problems.
In addition, the increase in power (with increasing peripheral speed) was also impractical for another reason. The energy consumers of the turbine were low-speed devices in comparison with it (electric generators were planned for this). Therefore, Laval had to develop special gearboxes for the kinematic connection of the turbine shaft to the consumer shaft.
The ratio of the masses and dimensions of the active Laval turbine and the gearbox to it.
Due to the large difference in the speed of these shafts, the gearboxes were extremely bulky and, in size and weight, often significantly exceeded the turbine itself. An increase in its power would entail an even greater increase in the size of such devices.
Eventually active Laval turbine was a relatively low-power unit (working units up to 350 hp), moreover expensive (due to a large set of improvements), and complete with a gearbox is also quite cumbersome. All this made it uncompetitive and excluded mass use.
An interesting fact is that the design principle of the active Laval turbine was not actually invented by him. Even 250 years before the advent of his research in Rome, in 1629, a book by the Italian engineer and architect Giovanni Branca titled "Le Machine" was published.
In it, among other mechanisms, a description of the "steam wheel" was placed, containing all the main units built by Laval: a steam boiler, a steam pipe (nozzle), an active turbine impeller and even a gearbox. Thus, long before Laval, all these elements were already known, and his merit was that he made them all really work together and dealt with extremely complex issues of improving the mechanism as a whole.
Steam active turbine by Giovanni Branca.
Interestingly, one of the most famous features of his turbine was the design of the nozzle (it was mentioned separately in the same patent) that supplies steam to the rotor blades. Here, the nozzle from the usual converging, as was the case in a jet turbine, became narrowing-expanding... Subsequently, this type of nozzle became known as Laval nozzle. They make it possible to accelerate the flow of gas (steam) to supersonic with rather low losses. About them .
Thus, the main problem, which Laval struggled with when developing his turbines, and which he could not cope with, was the high peripheral speed. However, a fairly effective solution to this problem has already been proposed and even, oddly enough, by Laval himself.
Multistage….
In the same year (1889), when the above-described active turbine was patented, the engineer developed an active turbine with two parallel rows of rotor blades mounted on one impeller (disk). It was the so-called two-stage turbine.
Steam was supplied to the rotor blades, as in a single-stage one, through a nozzle. A row of stationary blades was installed between two rows of rotor blades, which redirected the flow coming out of the blades of the first stage to the rotor blades of the second.
If we use the simplified principle proposed above for determining the peripheral speed for a single-stage jet turbine (Laval), it turns out that for a two-stage turbine, the rotation speed is less than the outflow velocity from the nozzle, not two, but four times.
The principle of the Curtis wheel and changing the parameters in it.
This is the very effective solution to the problem of low optimal peripheral speed, which Laval proposed, but did not use, and which is actively used in modern turbines, both steam and gas. Multistage ...
It means that the large energy available for the entire turbine can be divided in some way into parts according to the number of stages, and each such part is triggered in a separate stage. The lower this energy, the lower the speed of the working fluid (steam, gas) entering the rotor blades and, therefore, the lower the optimal peripheral speed.
That is, by changing the number of turbine stages, it is possible to change the rotational speed of its shaft and, accordingly, change the load on it. In addition, multistage operation allows the turbine to operate with large energy drops, that is, to increase its power, and at the same time maintain high efficiency rates.
Laval did not patent his two-stage turbine, although a prototype was made, so it bears the name of the American engineer C. Curtis (Curtis wheel (or disk)), who received a patent for a similar device in 1896.
However, much earlier, in 1884, the English engineer Charles Algernon Parsons developed and patented the first real multistage steam turbine... There were many statements by various scientists and engineers about the usefulness of dividing the available energy into steps before him, but he was the first to embody the idea in "iron".
Parsons multistage active jet turbine (disassembled).
Moreover, his turbine had a feature that brought it closer to modern devices. In it, steam expanded and accelerated not only in nozzles formed by stationary blades, but also partially in channels formed by specially profiled rotor blades.
This type of turbine is usually called reactive, although the name is rather arbitrary. In fact, it occupies an intermediate position between the purely reactive Heron-Laval turbine and the purely active Laval-Branc. The rotor blades, due to their design, combine the active and reactive principles in the overall process. Therefore, it would be more correct to call such a turbine active-reactive, which is often done.
Schematic diagram of a multistage Parsons turbine.
Parsons has worked on various types of multistage turbines. Among its designs were not only the above-described axial (the working body moves along the axis of rotation), but also radial (the steam moves in the radial direction). Quite well known is his three-stage purely active turbine "Geron", in which the so-called Heron's wheels are used (the essence is the same as that of the eolipil).
Jet turbine "Geron".
Later, from the early 1900s, steam turbine building rapidly gained momentum and Parsons was at its forefront. Its multistage turbines were used to equip sea vessels, at first experimental (the Turbinia ship, 1896, displacement 44 tons, speed 60 km / h - unprecedented for that time), then military (for example, the battleship Dreadnought, 18,000 tons, speed 40 km / h). h, turbine power 24,700 hp) and passenger (for example, the same type "Mauritania" and "Lusitania", 40,000 tons, speed 48 km / h, turbine power 70,000 hp). Stationary turbine construction began at the same time, for example by installing turbines as drives in power plants (Edison Company in Chicago).
About gas turbines ...
However, let us return to our main topic - aviation and note one rather obvious thing: such a clearly marked success in the operation of steam turbines could have for aviation, which is rapidly progressing in its development just at the same time, only of structural and fundamental importance.
The use of a steam turbine as a power plant on aircraft was, for obvious reasons, extremely dubious. Aircraft turbine could only become a fundamentally similar, but much more profitable gas turbine. However, not everything was so simple ...
According to Lev Gumilevsky, the author of the popular book "Engineers" in the 60s, once, in 1902, during the period of the rapid development of steam turbine engineering, Charles Parsons, in fact one of the main ideologists of this case at the time, was asked, in general, , a joking question: “ Is it possible to "parsonize" a gas engine?"(The turbine was meant).
The answer was expressed in an absolutely decisive manner: “ I think that a gas turbine will never be created. No two ways about it. " The engineer did not succeed in becoming a prophet, but he undoubtedly had reasons to say so.
The use of a gas turbine, especially if we bear in mind its use in aviation instead of steam, of course, was tempting, because its positive aspects are obvious. For all its power capabilities, it does not need huge, cumbersome devices for generating steam - boilers and also no less large devices and systems for its cooling - condensers, cooling towers, cooling ponds, etc.
The heater for the gas turbine engine is a small, compact, located inside the engine and burns fuel directly in the air stream. And he simply does not have a refrigerator. Or rather, it is there, but it exists as if virtually, because the exhaust gas is discharged into the atmosphere, which is the refrigerator. That is, there is everything you need for a heat engine, but at the same time everything is compact and simple.
True, a steam turbine plant can also do without a "real refrigerator" (without a condenser) and release steam directly into the atmosphere, but then you can forget about efficiency. An example of this is a steam locomotive - the real efficiency is about 6%, 90% of its energy flies into the pipe.
But with such tangible advantages, there are significant drawbacks, which, in general, became the basis for Parsons' categorical answer.
Compression of the working fluid for the subsequent implementation of the working cycle, incl. and in the turbine ...
In the working cycle of a steam turbine plant (Rankine cycle), the work of compressing water is small and the requirements for the pump performing this function and its efficiency are therefore also small. In the GTE cycle, where air is compressed, this work, on the contrary, is very impressive, and a large part of the available turbine energy is spent on it.
This reduces the proportion of useful work for which the turbine can be designed. Therefore, the requirements for the air compression unit in terms of its efficiency and economy are very high. Compressors in modern aircraft gas turbine engines (mainly axial), as well as in stationary units, along with turbines, are complex and expensive devices. About them .
Temperature…
This is the main problem for a gas turbine, including an aviation one. The fact is that if in a steam turbine plant the temperature of the working fluid after the expansion process is close to the temperature of the cooling water, then in a gas turbine it reaches a value of several hundred degrees.
This means that a large amount of energy is emitted into the atmosphere (like into a refrigerator), which, of course, negatively affects the efficiency of the entire working cycle, which is characterized by thermal efficiency: η t = Q 1 - Q 2 / Q 1. Here Q 2 is the same energy removed into the atmosphere. Q 1 - energy supplied to the process from the heater (in the combustion chamber).
In order to increase this efficiency, it is necessary to increase Q 1, which is equivalent to an increase in temperature in front of the turbine (that is, in the combustion chamber). But the fact of the matter is that it is far from always possible to raise this temperature. Its maximum value is limited by the turbine itself and strength becomes the main condition here. The turbine operates under very harsh conditions when high temperatures are combined with high centrifugal loads.
It is this factor that has always limited the power and traction capabilities of gas turbine engines (largely dependent on temperature) and often became the reason for the complication and rise in the cost of turbines. This situation has remained in our time.
And in the days of Parsons, neither the metallurgical industry nor aerodynamic science could yet provide a solution to the problems of creating an efficient and economical compressor and high-temperature turbine. There was no corresponding theory, nor the necessary heat-resistant and heat-resistant materials.
And yet there were attempts ...
Nevertheless, as usually happens, there were people who were not afraid (or maybe they did not understand :-)) of possible difficulties. Attempts to create a gas turbine did not stop.
Moreover, it is interesting that Parsons himself, at the dawn of his "turbine" activity, in his first patent for a multistage turbine, noted the possibility of its operation, in addition to steam, also on fuel combustion products. A possible variant of a gas turbine engine running on liquid fuel with a compressor, a combustion chamber and a turbine was also considered there.
Smoke spit.
Examples of using gas turbines without any theory have been known for a long time. Apparently, even Geron used the principle of an air jet turbine in the "theater of automata". The so-called "smoke skewers" are widely known.
And in the already mentioned book of the Italian (engineer, architect, Giovanni Branca, Le Machine) Giovanni Branca there is a drawing “ Fiery wheel". In it, the turbine wheel rotates with combustion products from a fire (or hearth). Interestingly, Branca himself did not build most of his machines, but only expressed ideas for their creation.
"Wheel of Fire" by Giovanni Branca.
In all these "smoke and fire wheels" there was no stage of air (gas) compression, and there was no compressor as such. The transformation of potential energy, that is, the supplied thermal energy of fuel combustion, into kinetic (acceleration) for the rotation of the gas turbine occurred only due to the action of gravity, when warm masses rose upward. That is, the phenomenon of convection was used.
Of course, such "units" for real machines, for example, for a drive Vehicle could not be used. However, in 1791, the Englishman John Barber patented a "horseless car", one of the most important components of which was a gas turbine. It was the first ever officially registered patent for a gas turbine.
John Barber's gas turbine engine.
The machine used gas obtained from wood, coal or oil, heated in special gas generators (retorts), which, after cooling, entered a piston compressor, where it was compressed together with air. Then the mixture was fed into the combustion chamber, and after that the combustion products were rotated turbine... Water was used to cool the combustion chambers, and the resulting steam was also directed to the turbine.
The level of development of the then technologies did not allow to bring the idea to life. The working model of the Barber machine with a gas turbine was only built in 1972 by Kraftwerk-Union AG for the Hanover Industrial Exhibition.
Throughout the 19th century, the development of the gas turbine concept was extremely slow for the reasons described above. There were few examples worthy of attention. The compressor and heat remained an insurmountable stumbling block. There have been attempts to use a fan to compress air, and to use water and air to cool structural elements.
F. Stolze's engine. 1 - axial compressor, 2 - axial turbine, 3 - heat exchanger.
There is an example of a gas turbine engine by the German engineer Franz Stolze, patented in 1872 and very similar in design to modern gas turbine engines. In it, a multistage axial compressor and a multistage axial turbine were located on the same shaft.
The air after passing through the regenerative heat exchanger was divided into two parts. One entered the combustion chamber, the second was mixed with the combustion products before entering the turbine, reducing their temperature. This is the so-called secondary air, and its use is a technique widely used in modern gas turbine engines.
The Stolze engine was tested in 1900-1904, but it turned out to be extremely ineffective due to the poor quality of the compressor and the low temperature in front of the turbine.
For most of the first half of the 20th century, the gas turbine could not actively compete with the steam turbine or become part of the GTE, which could adequately replace the piston internal combustion engine. Its application on engines was mainly auxiliary. For example, as pressurization units v piston engines, including aviation.
But from the beginning of the 40s, the situation began to change rapidly. Finally, new high-temperature alloys were created, which made it possible to radically raise the gas temperature in front of the turbine (up to 800 ° C and above), and quite economical ones with high efficiency appeared.
This not only made it possible to build efficient gas turbine engines, but also, due to the combination of their power with relative lightness and compactness, to use them on aircraft. The era of jet aircraft and aircraft gas turbine engines began.
Turbines in aviation gas turbine engines ...
So ... The main field of application of turbines in aviation is gas turbine engines. The turbine does the hard work here - it turns the compressor. Moreover, in the GTE, as in any other heat engine, the expansion work is larger than the compression work.
And the turbine is exactly the expansion machine, and it consumes only a part of the available energy of the gas flow for the compressor. The remainder (sometimes called free energy) can be used for useful purposes depending on the type and design of the engine.
Scheme of TVAD Makila 1a1 with a free turbine.
Turboshaft engine AMAKILA 1A1.
For indirect reaction engines, such as (helicopter GTE), it is spent on the rotation of the propeller. In this case, the turbine is usually split into two parts. The first is compressor turbine... The second, driving the screw, is the so-called free turbine... It rotates independently and is connected to the compressor turbine only gas-dynamically.
In direct reaction engines (jet engines or WFD), the turbine is used only to drive the compressor. The remaining free energy, which rotates the free turbine in the TWAD, is triggered in the nozzle, converting into kinetic energy to obtain jet thrust.
In the middle between these extremes are located. They use part of the free energy to drive the propeller, and some part forms a jet thrust in the output device (nozzle). True, its share in the total engine thrust is small.
Diagram of a single-shaft HPT DART RDa6. Turbine on a common engine shaft.
Rolls-Royce DART RDa6 single-shaft turboprop engine.
By design, the turbine engine can be single-shaft, in which the free turbine is not structurally distinguished and, being one unit, immediately drives both the compressor and the propeller. An example of a Rolls-Royce DART RDa6 theater, as well as our famous AI-20 theater.
There can also be a turbine engine with a separate free turbine that drives the propeller and is not mechanically connected to the rest of the engine components (gas-dynamic connection). An example is the PW127 engine of various modifications (aircraft), or the Pratt & Whitney Canada PT6A theater.
Schematic of the Pratt & Whitney Canada PT6A turbine engine with a free turbine.
Pratt & Whitney Canada PT6A engine.
Scheme of the PW127 turbine engine with a free turbine.
Of course, in all types of gas turbine engines to payload also include units that ensure the operation of the engine and aircraft systems. These are usually pumps, fuel and hydro-, electric generators, etc. All of these devices are most often driven from the turbocharger shaft.
On the types of turbines.
There are actually a lot of types. Just for example, some names: axial, radial, diagonal, radial-axial, rotary-blade, etc. In aviation, only the first two are used, and radial is quite rare. Both of these turbines were named according to the nature of the movement of the gas flow in them.
Radial.
In the radial, it flows radially. Moreover, in the radial aircraft turbine a centripetal direction of flow is used, which provides a higher efficiency (in non-aviation practice, there is also a centrifugal one).
The stage of a radial turbine consists of an impeller and stationary blades that form a flow at the inlet to it. The blades are profiled so that the interscapular channels have a tapering configuration, that is, they are nozzles. All these blades, together with the housing elements on which they are mounted, are called nozzle.
Diagram of a radial centripetal turbine (with explanations).
The impeller is an impeller with specially profiled blades. The spinning of the impeller occurs when the gas passes in the converging channels between the blades and the action on the blades.
Radial centripetal turbine impeller.
Radial turbines quite simple, their impellers have a small number of blades. The possible peripheral speeds of a radial turbine at the same stresses in the impeller are higher than those of an axial one, therefore, larger amounts of energy (heat drops) can be triggered on it.
However, these turbines have a small flow area and do not provide sufficient gas flow at the same size compared to axial turbines. In other words, they have too large relative diametrical dimensions, which complicates their arrangement in a single engine.
In addition, it is difficult to create multistage radial turbines due to large hydraulic losses, which limits the degree of gas expansion in them. It is also difficult to carry out cooling of such turbines, which reduces the value of the possible maximum gas temperatures.
Therefore, the use of radial turbines in aviation is limited. They are mainly used in low-power units with low gas consumption, most often in auxiliary mechanisms and systems, or in engines of model aircraft and small unmanned aircraft.
First jet, the Heinkel He 178.
Turbojet engine Heinkel HeS3 with radial turbine.
One of the few examples of the use of a radial turbine as a component of a cruising aircraft WFD is the engine of the first real jet, the Heinkel He 178, the turbojet Heinkel HeS 3. The photo clearly shows the elements of the stage of such a turbine. The parameters of this engine were quite consistent with the possibility of its use.
Axial aircraft turbine.
This is the only type of turbine currently used in cruise aircraft GTEs. The main source of mechanical work on the shaft obtained from such a turbine in the engine is the impellers or, more precisely, the rotor blades (RL) installed on these wheels and interacting with the energetically charged gas flow (compressed and heated).
The crowns of fixed blades, installed in front of the workers, organize the correct direction of the flow and participate in the transformation of the potential energy of the gas into kinetic, that is, they accelerate it in the process of expansion with a drop in pressure.
These blades, complete with the housing elements on which they are mounted, are called nozzle(CA). The nozzle assembly complete with rotor blades is turbine stage.
The essence of the process ... Generalization of what was said ...
In the process of the aforementioned interaction with the rotor blades, the kinetic energy of the flow is converted into mechanical energy that rotates the engine shaft. This transformation in an axial turbine can take place in two ways:
An example of a single stage active turbine. Changes in parameters along the path are shown.
1. Without changing the pressure, and hence the value of the relative flow velocity (only its direction is noticeably changing - the flow turn) in the turbine stage; 2. With a drop in pressure, an increase in the relative flow rate and some change in its direction in the stage.
Turbines operating according to the first method are called active. The gas flow actively (impulsively) acts on the blades due to a change in its direction when flowing around them. In the second way - jet turbines... Here, in addition to the impulse effect, the flow acts on the rotor blades also indirectly (to put it simply), with the help of reactive force, which increases the power of the turbine. An additional reactive effect is achieved due to the special profiling of the rotor blades.
The concepts of activity and reactivity in general for all turbines (not only aviation ones) were mentioned above. However, in modern aviation GTEs, only axial jet turbines are used.
Change of parameters in a stage of an axial gas turbine.
Since the force effect on the radar is double, such axial turbines are also called active-reactive, which is perhaps more correct. This type of turbine is more aerodynamically advantageous.
The stationary blades of the nozzle apparatus included in the stage of such a turbine have a large curvature, due to which the cross-section of the interscapular channel decreases from the inlet to the outlet, that is, the section f 1 is less than the section f 0. The profile of the converging jet nozzle is obtained.
The following rotor blades also have a large curvature. In addition, with respect to the incoming flow (vector W 1), they are located so as to avoid stalling and to ensure correct flow around the blade. At certain radii, the RL also form tapering interscapular channels.
Step work aircraft turbine.
The gas approaches the nozzle apparatus with a direction of motion close to the axial one and with a velocity of C 0 (subsonic). The pressure in the stream is P 0, the temperature is T 0. Passing the interscapular channel, the flow accelerates to a speed of С 1 with a rotation to an angle α 1 = 20 ° - 30 °. In this case, the pressure and temperature drop to the values of P 1 and T 1, respectively. Part of the potential energy of the flow is converted into kinetic energy.
Gas flow pattern in the axial turbine stage.
Since the rotor blades move with a peripheral speed U, then the flow enters the interscapular channel of the RL with a relative speed W 1, which is determined by the difference between C 1 and U (vector). Passing through the channel, the flow interacts with the blades, creating aerodynamic forces P on them, the circumferential component of which P u makes the turbine rotate.
Due to the narrowing of the channel between the blades, the flow is accelerated to the speed W 2 (reactive principle), while its rotation also occurs (active principle). The absolute flow rate С 1 decreases to С 2 - the kinetic energy of the flow is converted into mechanical energy on the turbine shaft. The pressure and temperature drop to values of P 2 and T 2, respectively.
The absolute speed of the flow when passing the stage increases slightly from C 0 to the axial projection of the speed C 2. In modern turbines, this projection has a magnitude of 200 - 360 m / s for the stage.
The step is profiled so that the angle α 2 is close to 90 °. The difference is usually 5-10 °. This is done so that the value of C 2 is minimal. This is especially important for the last stage of the turbine (at the first or middle stages, a deviation from a right angle up to 25 ° is allowed). The reason for this is output speed loss, which just depend on the magnitude of the speed С 2.
These are the very losses that at one time did not give Laval the opportunity to raise the efficiency of his first turbine. If the engine is jet, then the remaining energy can be worked out in the nozzle. But, for example, for a helicopter engine that does not use jet thrust, it is important that the flow rate behind the last stage of the turbine is as low as possible.
Thus, in the stage of an active-reactive turbine, gas expansion (decrease in pressure and temperature), transformation and operation of energy (heat drop) occurs not only in the SA, but also in the impeller. The distribution of these functions between the RK and the CA is characterized by a parameter of the theory of engines, called degree of reactivity ρ.
It is equal to the ratio of the heat drop in the impeller to the heat drop in the entire stage. If ρ = 0, then the stage (or the entire turbine) is active. If ρ> 0, then the stage is reactive or, more precisely, for our case, active-reactive. Since the profiling of the rotor blades changes along the radius, this parameter (as well as some others) is calculated by the average radius (section B-B in the figure of the change in parameters in the step).
The configuration of the blade of the active-jet turbine.
Pressure change along the length of the RL blade of an active-reactive turbine.
For modern gas turbine engines, the degree of turbine reactivity is in the range of 0.3-0.4. This means that only 30-40% of the total heat drop of a stage (or turbine) is triggered in the impeller. 60-70% is triggered in the nozzle apparatus.
Something about losses.
As already mentioned, any turbine (or its stage) converts the flow energy supplied to it into mechanical work. However, in a real unit, this process can have different efficiency. Part of the available energy is necessarily wasted, that is, it turns into losses, which must be taken into account and measures must be taken to minimize them in order to increase the efficiency of the turbine, that is, to increase its efficiency.
Losses consist of hydraulic and loss with output speed... Hydraulic losses include profile and end losses. Profile - this is, in fact, friction losses, since the gas, having a certain viscosity, interacts with the surfaces of the turbine.
Typically, such losses in the impeller are about 2-3%, and in the nozzle apparatus - 3-4%. Measures to reduce losses consist in "ennobling" the flow path by calculation and experiment, as well as the correct calculation of the velocity triangles for the flow in the turbine stage, more precisely, the choice of the most advantageous peripheral speed U at a given speed C 1. These actions are usually characterized by the parameter U / C 1. The peripheral speed at the average radius in the turbojet engine is 270 - 370 m / s.
The hydraulic perfection of the flow path of the turbine stage takes into account such a parameter as adiabatic efficiency... Sometimes it is also called scapular, because it takes into account the friction losses in the stage blades (CA and RL). There is one more efficiency for a turbine, which characterizes it precisely as a unit for generating power, that is, the degree to which the available energy is used to create work on the shaft.
This is the so-called power (or effective) efficiency... It is equal to the ratio of the work on the shaft to the available heat drop. This efficiency takes into account the losses with the output speed. They usually amount to about 10-12% for a turbojet engine (in modern turbojet engines, C 0 = 100 -180 m / s, C 1 = 500-600 m / s, C 2 = 200-360 m / s).
For modern GTE turbines, the adiabatic efficiency is about 0.9 - 0.92 for uncooled turbines. If the turbine is cooled, then this efficiency can be lower by 3-4%. Power efficiency is usually 0.78 - 0.83. It is less than the adiabatic one by the amount of losses with the output speed.
As for the end losses, these are the so-called " overflow loss". The flow path cannot be absolutely isolated from the rest of the engine due to the presence of rotating units in combination with stationary ones (housing + rotor). Therefore, gas from areas with increased pressure tends to flow into areas with reduced pressure. In particular, for example, from the area in front of the rotor blade to the area behind it through the radial clearance between the blade airfoil and the turbine casing.
Such a gas does not participate in the process of converting the flow energy into mechanical, because it does not interact with the blades in this regard, that is, end losses (or radial clearance loss). They make up about 2-3% and negatively affect both the adiabatic and power efficiency, reduce the efficiency of the gas turbine engine, and quite noticeably.
It is known, for example, that an increase in the radial clearance from 1 mm to 5 mm in a turbine with a diameter of 1 m can lead to an increase in the specific fuel consumption in the engine by more than 10%.
It is clear that it is impossible to completely get rid of the radial clearance, but they are trying to minimize it. It's hard enough because aircraft turbine- the unit is heavily loaded. Accurate accounting of all factors affecting the size of the gap is difficult enough.
The engine operating modes often change, which means that the deformations of the rotor blades, the disks on which they are fixed, and the turbine housings change as a result of changes in the values of temperature, pressure and centrifugal forces.
Labyrinth seal.
Here it is necessary to take into account the amount of permanent deformation during long-term operation of the engine. Plus, the evolutions performed by the aircraft affect the deformation of the rotor, which also changes the size of the clearances.
Usually, the clearance is estimated after stopping a warm engine. In this case, the thin outer casing cools down faster than the massive disks and shaft and, decreasing in diameter, touches the blades. Sometimes the value of the radial clearance is simply chosen in the range of 1.5-3% of the length of the blade airfoil.
The principle of honeycomb sealing.
In order to avoid damage to the blades, if they touch the turbine housing, special inserts made of a material softer than the material of the blades are often placed in it (for example, cermets). In addition, non-contact seals are used. These are usually labyrinthine or honeycomb labyrinth seals.
In this case, the rotor blades are bandaged at the ends of the feather and seals or wedges (for honeycombs) are already placed on the banding shelves. In honeycomb seals, due to the thin walls of the honeycomb, the contact area is very small (10 times smaller than the usual labyrinth), so the assembly of the unit is carried out without a gap. After running-in, the gap is approximately 0.2 mm.
Application of a honeycomb seal. Comparison of losses when using honeycomb (1) and smooth ring (2).
Similar methods of sealing gaps are used to reduce gas leakage from the flow path (for example, into the disk space).
SAURZ ...
These are the so-called passive methods radial clearance control. In addition, on many gas turbine engines, developed (and developed) since the end of the 80s, the so-called " systems for active regulation of radial clearances"(SAURZ - active method). These are automatic systems, and the essence of their work is to control the thermal inertia of the housing (stator) of an aircraft turbine.
The rotor and stator (outer casing) of the turbine differ from each other in material and in "massiveness". Therefore, in transient modes, they expand in different ways. For example, when the engine changes from a reduced mode of operation to an increased, high-temperature, thin-walled body faster (than a massive rotor with discs)) heats up and expands, increasing the radial clearance between itself and the blades. Plus, changes in the pressure in the tract and the evolution of the aircraft.
To avoid this, automatic system(usually the main regulator of the FADEC type) organizes the supply of cooling air to the turbine housing in the required quantities. Thus, the heating of the housing is stabilized within the required limits, which means that the value of its linear expansion and, accordingly, the value of the radial clearances change.
All this saves fuel, which is very important for modern civil aviation. The most effective SAURZ systems are used in low-pressure turbines on a turbojet engine such as GE90, Trent 900, and some others.
Much less often, however, it is quite effective to synchronize the heating rates of the rotor and stator by forced blowing of the turbine discs (and not the housing). These systems are used on the CF6-80 and PW4000 engines.
———————-
In the turbine, axial clearances are also regulated. For example, between the trailing edges of the CA and the input RL, there is usually a gap in the range of 0.1-0.4 from the RL chord at the average radius of the blades. The smaller this gap, the less the flow energy loss behind the CA (for friction and equalization of the velocity field behind the CA). But at the same time, the RL vibration grows due to the alternate hit from the areas behind the CA blade bodies into the interscapular areas.
A little general about the design ...
Axial aircraft turbines modern gas turbine engines in constructive terms can have different the shape of the flow path.
Dav = (Dvn + Dn) / 2
1. Form with constant body diameter (Dн). Here, the inner and average diameters along the path decrease.
Constant outer diameter.
Such a scheme fits well into the dimensions of the engine (and the aircraft fuselage). It has a good distribution of work on the stages, especially for twin-shaft turbojet engines.
However, in this scheme, the so-called bell angle is large, which is fraught with flow separation from the inner walls of the housing and, consequently, hydraulic losses.
Constant inner diameter.
When designing, they try not to allow a bell angle of more than 20 °.
2. Form with constant inner diameter (Dv).
The average diameter and the diameter of the body increase along the path. Such a scheme does not fit well into the dimensions of the engine. In a turbojet engine, due to the "runaway" of the flow from the inner housing, it is necessary to turn it on the SA, which entails hydraulic losses.
Constant average diameter.
The scheme is more appropriate for use in turbojet engine.
3. Form with constant average diameter (Dav). The diameter of the body increases, the inner diameter decreases.
The scheme has the disadvantages of the previous two. But at the same time, the calculation of such a turbine is quite simple.
Modern aircraft turbines are often multistage. The main reason for this (as mentioned above) is the large available energy of the turbine as a whole. To ensure the optimal combination of the peripheral speed U and the speed C 1 (U / C 1 is optimal), and therefore high overall efficiency and good economy, it is necessary to distribute all available energy in stages.
An example of a three-stage turbojet turbine.
At the same time, however, herself turbine structurally becomes more complicated and heavier. Due to the small temperature difference at each stage (it is distributed over all stages), a large number of the first stages are exposed to high temperatures and often require additional cooling.
Four-stage axial-flow turbine of the HPT.
The number of stages may vary depending on the type of engine. For turbojet engines, usually up to three, for two-circuit engines up to 5-8 stages. Usually, if the engine is multi-shaft, then the turbine has several (according to the number of shafts) stages, each of which drives its own unit and itself can be multistage (depending on the degree of bypass).
Twin-shaft axial aircraft turbine.
For example, in a three-shaft Rolls-Royce Trent 900 engine, the turbine has three stages: one-stage for driving the compressor high pressure, one-stage for the intermediate compressor drive and five-stage for the fan drive. The joint operation of the cascades and the determination of the required number of stages in the cascades is described separately in the "theory of engines".
Itself aircraft turbine, in simple terms, is a structure consisting of a rotor, a stator and various auxiliary structural elements. The stator consists of an outer casing, casings nozzles and rotor bearing housings. The rotor is usually a disc structure in which the discs are connected to the rotor and to each other using various additional elements and fastening methods.
An example of a single-stage turbojet turbine. 1 - shaft, 2 - CA blades, 3 - impeller disk, 4 - rotor blades.
On each disk, as the base of the impeller, there are rotor blades. When designing, the blades are tried to be made with a smaller chord in view of the smaller width of the rim of the disk on which they are installed, which reduces its mass. But at the same time, in order to maintain the parameters of the turbine, it is necessary to increase the length of the feather, which may entail banding the blades to increase the strength.
Possible types of locks for fastening the rotor blades in the turbine disk.
The paddle is attached to the disc using lock connection. Such a connection is one of the most loaded structural elements in a gas turbine engine. All loads perceived by the blade are transferred to the disk through the lock and reach very large values, especially since due to the difference in materials, the disk and blades have different coefficients of linear expansion, and besides, due to the unevenness of the temperature field, they heat up differently.
In order to assess the possibility of reducing the load in the lock connection and thereby increasing the reliability and service life of the turbine, research work is being carried out, among which experiments on bimetallic blades or the use of blisk impellers in turbines.
When using bimetallic blades, the loads in the locks of their attachment to the disk are reduced due to the manufacture of the blade lock from a material similar to the material of the disk (or similar in parameters). The blade feather is made of another metal, after which they are connected using special technologies (bimetal is obtained).
Blinks, that is, impellers, in which the blades are made in one piece with the disk, generally exclude the presence of a lock connection, and therefore unnecessary stresses in the material of the impeller. Units of this type are already used in modern turbojet engine compressors. However, for them, the issue of repair becomes much more complicated and the possibilities of high-temperature use and cooling in aircraft turbine.
An example of fastening rotor blades in a disk using herringbone locks.
The most common way of attaching blades in heavily loaded turbine discs is the so-called herringbone. If the loads are moderate, then other types of locks can be used, which are simpler in design, for example, cylindrical or T-shaped.
Control…
Since the working conditions aircraft turbine extremely difficult, and the issue of reliability, as the most important unit of the aircraft has a primary priority, then the problem of monitoring the state of structural elements is in the first place in ground operation. This is especially true for monitoring the internal cavities of the turbine, where the most loaded elements are located.
Inspection of these cavities is, of course, impossible without the use of modern equipment. remote visual control... For aircraft gas turbine engines, various types of endoscopes (borescopes) act in this capacity. Modern devices of this type are quite advanced and have great capabilities.
Inspection of the air-gas duct of the TVRD using the Vucam XO endoscope.
A vivid example is the Vucam XO portable measuring video endoscope of the German company ViZaar AG. With its small size and weight (less than 1.5 kg), this device is nevertheless very functional and has impressive capabilities for both inspection and processing of the information received.
Vucam XO is absolutely mobile. His entire set is housed in a small plastic case. The video probe with a large number of easily replaceable optical adapters has a full articulation of 360 °, with a diameter of 6.0 mm and can be of various lengths (2.2 m; 3.3 m; 6.6 m).
Borescopic examination of a helicopter engine using a Vucam XO endoscope.
Borescopic inspections using such endoscopes are included in the regulations for all modern aircraft engines. In turbines, the flow path is usually inspected. The endoscope probe penetrates the internal cavities aircraft turbine through special control ports.
Borescopic inspection ports on the casing of the TVRD CFM56 turbine.
They are holes in the turbine casing, closed with sealed plugs (usually threaded, sometimes spring-loaded). Depending on the capabilities of the endoscope (probe length), it may be necessary to rotate the motor shaft. The blades (CA and RL) of the first stage of the turbine can be inspected through the windows on the body of the combustion chamber, and the last stage through the engine nozzle.
That will raise the temperature ...
One of the general directions of development of gas turbine engines of all schemes is to increase the gas temperature in front of the turbine. This allows a significant increase in thrust without increasing air consumption, which can lead to a decrease in the frontal area of the engine and an increase in specific frontal thrust.
In modern engines, the gas temperature (after the flame) at the exit from the combustion chamber can reach 1650 ° C (with a tendency to increase), therefore, for the normal operation of the turbine at such high thermal loads, it is necessary to take special, often protective measures.
The first (and most downtime of this situation)- usage heat-resistant and heat-resistant materials, both metal alloys and (in the future) special composite and ceramic materials, which are used for the manufacture of the most loaded parts of the turbine - nozzle and rotor blades, as well as disks. The most loaded of them are, perhaps, the working blades.
Metal alloys are mainly nickel-based alloys (melting point - 1455 ° C) with various alloying additions. In modern heat-resistant and heat-resistant alloys, up to 16 names of various alloying elements are added to obtain maximum high-temperature characteristics.
Chemical exotic ...
Among them, for example, chromium, manganese, cobalt, tungsten, aluminum, titanium, tantalum, bismuth and even rhenium, or instead of ruthenium and others. Rhenium is especially promising in this regard (Re is rhenium, used in Russia), which is now used instead of carbides, but it is extremely expensive and its reserves are small. The use of niobium silicide is also considered promising.
In addition, the surface of the blade is often coated with a special technology applied heat-shielding layer(anti-thermal coating - thermal-barrier coating or TVS) , significantly reducing the amount of heat flow into the blade body (thermal barrier functions) and protecting it from gas corrosion (heat-resistant functions).
An example of a thermal protective coating. The nature of the temperature change over the blade section is shown.
The figure (microphoto) shows a heat-shielding layer on a blade of a high-pressure turbine of a modern turbojet engine. Here TGO (Thermally Grown Oxide) is a thermally growing oxide; Substrate - the main material of the blade; Bond coat is a transition layer. The composition of fuel assemblies now includes nickel, chromium, aluminum, yttrium, etc. Experimental work is also being carried out on the use of ceramic coatings based on zirconium oxide stabilized with zirconium oxide (developed by VIAM).
For example…
The heat-resistant nickel alloys of the Special Metals Corporation - USA, containing at least 50% nickel and 20% chromium, as well as titanium, aluminum and many other components added in small quantities ...
Depending on the profile purpose (RL, CA, turbine disks, flow path elements, nozzles, compressors, etc., as well as non-aeronautical applications), their composition and properties, they are combined into groups, each of which includes various types of alloys.
Rolls-Royce Nene engine turbine blades made of Nimonic 80A alloy.
Some of these groups are: Nimonic, Inconel, Incoloy, Udimet / Udimar, Monel and others. For example, Nimonic 90 alloy, developed back in 1945 and used to make elements aircraft turbines(mainly blades), nozzles and parts of aircraft, has the following composition: nickel - minimum 54%, chromium - 18-21%, cobalt - 15-21%, titanium - 2-3%, aluminum - 1-2%, manganese - 1%, zirconium -0.15% and other alloying elements (in small amounts). This alloy is produced to this day.
In Russia (USSR), the development of this type of alloys and other important materials for gas turbine engines was and is being successfully carried out by VIAM (All-Russian Research Institute of Aviation Materials). In the post-war period, the institute developed wrought alloys (type EI437B), since the beginning of the 60s it has created a whole series of high-quality cast alloys (more on that below).
However, practically all heat-resistant metal materials can withstand temperatures up to about 1050 ° C without cooling.
That's why:
The second, widely used measure, this application various cooling systems blades and other structural elements aircraft turbines... It is still impossible to do without cooling in modern gas turbine engines, despite the use of new high-temperature heat-resistant alloys and special methods of manufacturing elements.
There are two areas of cooling systems: systems open and closed... Closed systems can use forced circulation of the heat carrier fluid in the blade-radiator system, or they can use the principle of "thermosyphon effect".
In the latter method, the movement of the coolant occurs under the action of gravitational forces, when warmer layers displace colder ones. As a heat carrier here, for example, sodium or an alloy of sodium and potassium can be used.
However, closed systems are not used in aviation practice due to the large number of difficult-to-solve problems and are at the stage of experimental research.
An approximate cooling scheme for a multistage turbojet turbine. Shown are the seals between the CA and the rotor. A - a lattice of profiles for swirling the air for the purpose of its preliminary cooling.
But in wide practical application are open cooling systems... The refrigerant here is air, which is usually supplied under different pressures due to the different stages of the compressor inside the turbine blades. Depending on the maximum value of the gas temperature at which it is advisable to use these systems, they can be divided into three types: convective, convective-film(or obstructive) and porous.
With convective cooling, air is supplied inside the blade through special channels and, washing the hottest areas inside it, goes out into the flow in the area with a lower pressure. In this case, various schemes for organizing the flow of air in the blades can be used, depending on the shape of the channels for it: longitudinal, transverse or loop-shaped (mixed or complicated).
Types of cooling: 1 - convective with a deflector, 2 - convective-film, 3 - porous. Blade 4 is a heat-shielding coating.
The simplest scheme with longitudinal channels along the feather. Here, the air outlet is usually organized in the upper part of the blade through the shroud. In such a scheme, there is a rather large temperature unevenness along the blade airfoil - up to 150-250˚, which adversely affects the strength properties of the blade. The circuit is used on engines with gas temperatures up to ≈ 1130 ° C.
Another way convective cooling(1) implies the presence of a special deflector inside the feather (thin-walled shell - inserted inside the feather), which facilitates the supply of cooling air first to the most heated areas. The deflector forms a kind of nozzle that blows air into the front of the blade. It turns out jet cooling of the most heated part. Further, the air, washing the rest of the surface, comes out through the longitudinal narrow holes in the feather.
Turbine blade for CFM56 engine.
In such a scheme, the temperature unevenness is much lower, in addition, the deflector itself, which is inserted into the blade under interference along several centering transverse belts, due to its elasticity, serves as a damper and dampens the vibrations of the blades. This scheme is used at a maximum gas temperature of ≈ 1230 ° C.
The so-called half-loop scheme makes it possible to achieve a relatively uniform temperature field in the blade. This is achieved by experimentally selecting the location of various ribs and pins that direct the air flows inside the blade body. This scheme allows a maximum gas temperature of up to 1330 ° C.
The nozzle blades are convectively cooled in the same way as the blades. They are usually double-cavity with additional ribs and pins to intensify the cooling process. Air of a higher pressure is supplied to the front cavity at the leading edge than to the rear (due to different compressor stages) and is released into various zones of the duct in order to maintain the minimum required pressure difference to ensure the required air velocity in the cooling channels.
Examples of possible ways to cool rotor blades. 1 - convective, 2 - convective-film, 3 - convective-film with complicated loop channels in the blade.
Convective film cooling (2) is used at an even higher gas temperature - up to 1380 ° C. With this method, part of the cooling air is released through special holes in the blade onto its outer surface, thereby creating a kind of barrier film which protects the blade from contact with the hot gas flow. This method is used for both rotor blades and nozzle blades.
The third method is porous cooling (3). In this case, the power rod of the blade with longitudinal channels is covered with a special porous material, which allows for a uniform and metered release of the coolant to the entire blade surface washed by the gas flow.
This is still a promising method, which is not used in the mass practice of using gas turbine engines due to the difficulties with the selection of a porous material and a high probability of a fairly rapid clogging of pores. However, in the case of solving these problems, the presumably possible gas temperature with this type of cooling can reach 1650 ° C.
The turbine disks and the CA housings are also cooled by air due to the various stages of the compressor when it passes through the internal cavities of the engine, washing the cooled parts and then discharging into the flow path.
Due to the rather high pressure increase in the compressors of modern engines, the cooling air itself can have a rather high temperature. Therefore, to increase the efficiency of cooling, measures are taken to preliminary reduce this temperature.
To do this, the air, before being fed into the turbine on the blades and disks, can be passed through special lattices of profiles, similar to the SA of the turbine, where the air is twisted in the direction of rotation of the impeller, expanding and cooling at the same time. The amount of cooling can be 90-160 °.
For the same cooling, air-to-air radiators cooled with secondary air can be used. On the AL-31F engine, such a radiator allows the temperature to drop to 220 ° in flight and 150 ° on the ground.
For cooling needs aircraft turbine a sufficiently large amount of air is drawn from the compressor. On various engines - up to 15-20%. This significantly increases the losses, which are taken into account in the thermogasdynamic calculation of the engine. On some engines, systems are installed that reduce the supply of air for cooling (or even close it altogether) at low engine operating conditions, which has a positive effect on efficiency.
Cooling scheme of the 1st stage of the turbine turbojet engine NK-56. Also shown are honeycomb seals and a tape for shutting off cooling at low engine operating conditions.
When evaluating the efficiency of the cooling system, additional hydraulic losses on the blades due to the change in their shape when the cooling air is released are usually taken into account. The efficiency of a real cooled turbine is about 3-4% lower than that of an uncooled one.
Something about making blades ...
On jet engines of the first generation, turbine blades were mainly manufactured by stamping with subsequent long-term processing. However, in the 50s, VIAM specialists convincingly proved that it is casting and not wrought alloys that open the prospect of increasing the level of heat resistance of blades. Gradually, a transition was made to this new direction (including in the West).
Currently, the production uses the technology of precision waste-free casting, which makes it possible to manufacture blades with specially profiled internal cavities, which are used for the operation of the cooling system (the so-called technology investment casting).
This is, in fact, the only way to obtain cooled blades now. He, too, has improved over time. At the first stages of the injection molding technology, blades with different sizes were produced. grains of crystallization, which did not reliably adhere to each other, which significantly reduced the strength and resource of the product.
Later, with the use of special modifiers, they began to produce cooled cast blades with uniform, equiaxed, fine structural grains. For this, VIAM in the 60s developed the first serial domestic heat-resistant alloys for casting ZhS6, ZhS6K, ZhS6U, VZhL12U.
Their operating temperature was 200 ° higher than that of the then widespread wrought (stamping) alloy EI437A / B (KhN77TYu / YR). The blades made from these materials worked for at least 500 hours without visually visible signs of destruction. This type of manufacturing technology is still used today. Nevertheless, grain boundaries remain weak point the structure of the blade, and it is along them that its destruction begins.
Therefore, with an increase in the load characteristics of the work of modern aircraft turbines(pressure, temperature, centrifugal loads), it became necessary to develop new technologies for the manufacture of blades, because the multi-grain structure did not in many ways satisfy the heavier operating conditions.
Examples of the structure of the refractory material of the rotor blades. 1 - equiaxial grain size, 2 - directional crystallization, 3 - single crystal.
This is how it appeared " directional crystallization method". With this method, in the solidified casting of the blade, not separate equiaxed metal grains are formed, but long columnar crystals, elongated strictly along the axis of the blade. This kind of structure significantly increases the resistance to fracture of the blade. It looks like a broom, which is very difficult to break, although each of the twigs that make up it breaks without problems.
This technology was subsequently refined to an even more progressive " monocrystalline casting method", When one blade is practically one whole crystal. This type of blades is now also installed in modern aircraft turbines... For their manufacture, special ones are used, including the so-called rhenium-containing alloys.
In the 70s and 80s, VIAM developed alloys for casting turbine blades with directional crystallization: ZhS26, ZhS30, ZhS32, ZhS36, ZhS40, VKLS-20, VKLS-20R; and in the 90s - long-life corrosion-resistant alloys: ZhSKS1 and ZhSKS2.
Further, working in this direction, VIAM from the beginning of 2000 to the present has created high-temperature heat-resistant alloys of the third generation: VZhM1 (9.3% Re), VZhM2 (12% Re), ZhS55 (9% Re) and VZhM5 (4% Re) ). To further improve the characteristics, experimental studies have been carried out over the past 10 years, which resulted in rhenium-ruthenium-containing alloys of the fourth - VZhM4 and fifth generations of VZhM6.
As assistants ...
As mentioned earlier, only jet (or active-jet) turbines are used in a gas turbine engine. However, in conclusion, it is worth remembering that among the used aircraft turbines there are also active ones. They mainly perform secondary tasks and do not take part in the operation of the main engines.
Nevertheless, their role is often very important. In this case, we are talking about air starters used to launch. There are various types of starter devices used to spin the rotors of gas turbine engines. The air starter is perhaps the most prominent among them.
Air starter turbojet engine.
This unit, in fact, despite the importance of functions, is fundamentally quite simple. The main unit here is a one- or two-stage active turbine, which rotates the engine rotor through a gearbox and a gearbox (in a turbojet engine, it is usually a low-pressure rotor).
The location of the air starter and its working line on the turbojet engine,
The turbine itself is spun up by a stream of air coming from a ground source, or an onboard APU, or from another aircraft engine that is already running. At a certain point in the starting cycle, the starter is automatically disengaged.
In such units, depending on the required output parameters, and radial turbines... They can also be used in air conditioning systems in aircraft cabins as an element of a turbo-cooler, in which the effect of expansion and temperature reduction of the air on the turbine is used to cool the air entering the cabins.
In addition, both active axial and radial turbines are used in turbocharging systems for piston aircraft engines. This practice began even before the transformation of the turbine into the most important unit of the gas turbine engine and continues to this day.
An example of the use of radial and axial turbines in auxiliary devices.
Similar systems using turbochargers are used in automobiles and in general in various compressed air supply systems.
Thus, the aircraft turbine also serves people in an auxiliary sense.
———————————
Well, that's probably all for today. In fact, there is still a lot more to write about in terms of additional information, and in terms of a more complete description of what has already been said. The topic is very broad. However, one cannot grasp the immensity :-). For general information, perhaps, enough. Thanks for reading to the end.
Until next time ...
At the end of the picture, "not fit" in the text.
An example of a single-stage turbojet turbine.
Model of Geron's eolipile at the Kaluga Museum of Cosmonautics.
Articulation of the video probe of the Vucam XO endoscope.
Vucam XO multifunctional endoscope screen.
Vucam XO endoscope.
An example of a thermal protective coating on the CA blades of a GP7200 engine.
Honeycomb plates used for seals.
Possible options for the elements of the labyrinth seal.
Labyrinth honeycomb seal.
