GB2075123A

GB2075123A - Turbine cooling air deswirler

Info

Publication number: GB2075123A
Application number: GB8109958A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1980-05-01
Filing date: 1981-03-31
Publication date: 1981-11-11
Also published as: GB2075123B; FR2481747A1; IT1168124B; DE3116923A1; DE3116923C2; IT8121454A1; IT8121454A0; FR2481747B1; JPS572428A; JPH0154524B2

Abstract

In order to direct nonrotating cooling air into a rotating turbine rotor 24 after stationary nozzles 34 have accelerated the cooling air in the direction of rotor 24 rotation, a diffuser-deswirler 36 rotating with the rotor directs this air; with curved and expanding flow passages, 38 into corresponding holes 32 in the turbine rotor. Significant pressure losses are avoided and a lower cooling air temperature also results. <IMAGE>

Description

SPECIFICATION Turbine cooling air deswirler This invention relates to cooling air flowpaths for high temperature turbines.

Recently, turbine engines have employed nozzles that are aimed in the direction of turbine rotation to accelerate this cooling air in the direction of ro rotation for ease of entry into the rotating shaft. The nozzle directs the air through simple holes drilled through the shaft wall. To reach the turbine blades, the air must pass through these holes in the shaft, then move radially outward into the hot turbine blades.

While this improvement has been employed with reasonable sucess, further gains are achievable. Analysis has shown that after exiting the turbine nozzle, the cooling air has a very high velocity that is actually greater than the rotational speed of the turbine shaft. This means the cooling air has a tangential velocity of the shaft. When the air slows down to pass through the shaft holes, a large pressure loss occurs. This represents an unrecoverable loss of energy. Also, if the air is flowing to a smaller radius, as in passing under a turbine disc, its tangential velocity will increase even more, sometimes actually causing an acoustic resonance. Recently turbine engines have employed flat radial vanes inside the turbine shaft to remove residual tangential velocity in the cooling air.This has been successful in eliminating acoustic resonance but has further increased the areodynamic losses in the cooling airflow system. These potential problems can be avoided by eliminating any excess tangential velocity of the cooling air before the air enters the turbine shaft.

It is, therefore, an object of the present invention to direct nonrotating cooling air into a rotating turbine section of a gas turbine engine without significant pressure losses and with lower resulting cooling air temperatures and reduced cooling airflow requirements.

It is another object of the present invention to direct cooling air into a rotating turbine section without excessive tangential velocity.

These and other objects will become more readily apparent from reference to the following description taken in conjunction with the appended drawings.

In one embodiment, the present invention is comprised of shaped turning vanes that correspond with, and are attached to, holes in a turbine shaft wall. The vanes are provided for turning the flow direction of cooling air that has been accelerated out of a nozzle in a direction that is tangent to the shaft wall, to a new direction that is parallel to the shaft hole centerlines. The vanes thereby direct the cooling air into the the rotating shaft holes without significant pressure losses and with a lower resultant cooling air temperature.

In addition, the vanes are provided with passages that expand in the direction of airflow for the purpose of diffusing the air and increasing static pressure. The entrance loss is reduced by providing an aerodynamically shaped inlet. This reduced entry loss combined with pressure recovery by diffusion permits the use of a higher pressure ratio nozzle which increases the effectiveness of the system and reduces the cooling air exit temperature relative to the rotor. Reduced cooling air temperature permits a reduction in cooling airflow and ultimately improves turbine cycle efficiency.

Figure 1 is a cross-sectional view of a typical gas turbine aircraft engine; Figure 2 is an enlarged cross-sectional view of a portion of a gas turbine engine showing a typical prior art cooling air path; Figure 3 is an enlarged cross-sectional view of a similar portion of a gas turbine engine, as that shown in Fig. 2, but incorporating one embodiment of the present invention; and Figure 4 is a cross-sectional view of one embodiment of a deswirler component of the present invention.

Referring now to Fig. 1, a gas turbine aircraft engine 10 is shown for the purpose of describing the basic components and functions of the engine and some general aspects of a cooling air flowpath. A description of the basic engine functions begins as incoming air enters a compressor 1 2 where it is compressed to a very high pressure that will support rapid combustion further downstream in the engine. This highly compressed air is directed through a compressor outlet 14 into a combustor 1 6 where the air is combined with fuel and ignited.The ignited air/fuel mixture forms hot combustion gases that accelerate from the combustor 1 6 into a turbine section 1 8. In the turbine section, these accelerated combustion gases are directed at turbine blades 20 causing them to rotate at very high velocities. The turbine blades 20 are connected owith rotors 22 to a turbine shaft 24 for the purpose of transferring power to the turbine shaft. The shaft 24 can be connected mechanically to whatever device the engine user wishes to drive mechanically. In a typical aircraft engine, the turbine shafts are used to drive both the compressor 1 2 and a fan (not shown) that accelerates air to provide forward thrust for an airplane.

In carrying out these basic engine functions, it must be appreciated that maximum power can be derived from the combustion gases at a certain thermodynamically determined optimum temperature. Unfortunately, the calculated best temperature is so high that operation of the engine in the optimum manner would quickly destroy engine parts exposed to the hot combustion gases. Therefore, gas turbine engines are actually run at a temperature somewhat below the thermody namically determined optimum level.

In efforts to improve engine efficiency by allowing higher temperature operation, recent design efforts have been directed at devising air-cooled turbine components in the combustion flowpath. These efforts have been very successful and have vastly improved the efficiency of the modern gas turbine engine. However, this cooling air must be derived from a high pressure source, such as the engine compressor 12, and any air taken from the engine compressor represents a parasitic loss in air available for combustion and a loss to engine power output.

In view of this parasitic loss, much effort has been directed at improved methods of handling this cooling air so that less air must be taken from the compressor 1 2 to cool the hot turbine parts.

Referring now to Fig. 2, a section of a prior art engine and an internal cooling air flowpath is shown. The path of the cooling airflow is generally depicted by the heavy shaded arrows. The cooling air flows from the compressor outlet (not shown in Fig. 2), to a region 25 surrounding a combustor wall 26, and eventually through a turbine shaft 24 into a turbine rotor cavity section 1 9. This is a very critical region of the cooling air flowpath because the air is being directed at the highest temperature turbine parts, including a first row of turbine blades 3Q. The air must be maintained at high pressure because in order to flow into and through the blades 20, the air must be higher in pressure than the combustion gases surrounding the nozzles and blades.Since the combustion gases have just left the compressor 1 2 and combustor 1 6, they are still at relatively high pressure in relation to the rest of the engine.

While this is a critical region of the cooling air flowpath, the technical difficulties of moving air in this region of the engine are further complicated because the air is flowing from a nonrotating section of the engine through a rotating shaft 24 into a rotor cavity 1 9. The air must be rapidly accelerated in a rotational direction where it enters the turbine shaft 24, generally through a plurality of holes 32 in the wall of the shaft. Significant inefficiencies and pressure changes can occur in this region where the nonrotating air Blows through the holes 32.

In an attempt to lessen these inefficiencies, engine designers have recently incorporated a nozzle device 34 in cooling air flowpaths of the type shown in Fig. 3. The nozzle 34 is provided to accelerate the cooling air in the direction of turbine rotation. As a result of this acceleration, the air is caused to flow in a direction tangential to the shaft circumference.

If the air has a tangential velocity greater than that of the shaft, a large pressure loss occurs when the air passes through the shaft holes.

In addition, if the air is flowing to a smaller radius, as in passing under a first stage turbine rotor 22, its tangential velocity will increase and this may cause an acoustic resonance. Eliminating the excess tangential velocity ahead of the shaft holes will significantly improve this situation, and that has been stated as an object of the present invention.

Referring now to Fig. 3, one embodiment of the present invention is shown where it has been incorporated into the region of the engine 10 where cooling air enters the turbine shaft 24. The invention incorporates a deswirler 36 mounted in the air flowpath where the air enters the shaft 24. The function of the deswirler 36 is to aerodynamically change the direction of flow of the cooling air and guide the air into the holes 32. The deswirler additionally functions to reduce rotational velocity so that it becomes similar in magnitude to the rotational velocity of the turbine shaft 24. The deswirler 36 is directly attached to the turbine shaft 24 so it rotates in exactly the same manner. This feature enables the deswirler 36 to reduce rotational velocity of the cooling air as the deswirler directs the air into the holes 32.

Another feature of one embodiment of the deswirler 36 that can be appreciated in Fig.

3, is the deswirler passages 38 can be formed with a cross-sectional area that expands from the deswirler entrance 40 to the deswirler exit 42. These continuously expanding passages 38 function as a diffuser thereby converting part of the air's approach velocity head into static pressure. Again, it must be emphasized this cooling air is directed into a high pressure area of the turbine, and it is very desirable to maintain high cooling air pressure at the point where the air enters the shaft holes 32. Therefore, in the particular application of the deswirler 36, shown in Fig. 3, it is highly desirable to expand its internal passages 38 and provide this diffusing function.

Referring now to Fig. 3, the nozzle 34, deswirler 36 and shaft holes 32 are shown in a manner such that the directional effects of the nozzles and deswirler on the cooling airflow can be readily appreciated. The flowpath of the cooling is depicted by the shaded arrows. In the course of this flowpath, the nozzles 34 are generally aligned in serial flow relationship with the deswirler entrances 40, and the deswirler exits 42 are similarly aligned with the shaft holes 32. This provides a generally aerodynamic flowpath for the cooling air.

As stated earlier, the cooling medium must be derived from a source of relatively high pressure air within the engine. One ideal location is the region 25 surrounding the combustor wall which is just downstream of the compressor outlet. This air is at very high pressure, and its location just upstream of the turbine section 113 permits routing into the turbine shaft 24.

The first step in diverting -this air into the turbine section 1 8 is to accelerate the air in the direction of turbine rotation. As described earlier, this is accomplished with the nozzle 34. The operation of a nozzle is well known to those skilled in the art, and any of a variety of types may be used to accelerate the air. The degree of cooling air acceleration can be varied by changing the nozzle construction.

After passing through the nozzle exits 44, the air is directed into the deswirler entrances 40. The deswirler 36 is comprised of a series of turning vanes 37 that form passages 38 for turning the airflow from the tangential direction to a direction more parallel with centerlines of the holes 32.

The vanes 37 accomplish this redirection by curving the airflow radially inward and simultaneously transforming some of the tangential velocity of the airflow into rotational velocity that generally matches the rotational velocity of the turbine shaft 34.

Additionaily, if the air has a tangential velocity that greatly exceeds the rotational velocity of the turbine shaft, the deswirler passages 38 are constructed to diffuse the air, converting part of the approach velocity head into static pressure as well as reducing entry loss into the shaft. This reduced entrance loss plus pressure recovery by diffusion permits a higher pressure ratio and acceleration across the nozzle 34. The higher pressure ratio across the nozzle 34 will cause a lower air temperature at the nozzle exit 44. Reduced cooling air temperature permits a reduction in cooling airflow, thus improving turbine efficiency and this is a primary object of tne present invention The reduction in cooling air tempera ure is accomplished by transferring some of the energy Gf the air to the turbine, further increasing its efficiency.

Claims

1. In a gas turbine engine having a compressor, a combustor, a rotating turbine sec tion arourd a central engine axis with associated turbine rotors and a rotating turbine shaft, and a cooling air circuit for providing cooling air into said rotating turbine section, said cooling air circuit having a nozzle for accelerating said cooling air in a direction tangential to said rotating turbine shaft and in the direction of turbine rotation, an improvement comprising: means fcr receiving said accelerated cooling air from said nozzle and for redirecting said cooling air to enter holes in said rotating turbine shaft without significant cooling air pressure losses.

2. The apparatus recited in claim 1, wherein said means comprises a rotating de swirled having passages with curved inner surfaces for progressively redirecting airflow into said shaft.

3. The apparatus recited in claim 2 wherein said passages have exits that are in serial flow relationship with centerlines of receiving holes in said rotating shaft.

4. The apparatus recited in claims 2 or 3 wherein said curved passages are of gradually increasing cross-sectional area for the purpose of diffusing the air thereby converting part of air approach velocity head into static pressure.

5. The apparatus recited in claims 2 or 3 wherein said deswirler is directly attached to said turbine shaft for rotation therewith.

6. In a gas turbine engine having a compressor, a combustor, a rotating turbine section around a central engine axis with associated turbine rotors and a rotating turbine shaft, and a cooling air circuit for providing cooling air into said rotating turbine section, said cooling air circuit having a nozzle for accelerating said cooling air in a direction tangential to said rotating turbine shaft and in the direction of turbine rotation, an improvement for directing this accelerated cooling air into said rotating turbine section without significant pressure losses, comprising: a diffuser type deswirler directly attached to said turbine shaft for rotation therewith, wherein said deswirler comprises internal vanes forming passages with progressively curved inner surfaces, wherein said passages further comprise: : (a) entrance regions between said vanes wherein said curved inner surfaces are aligned in serial flow relationship with accelerated cooling airflow exiting said nozzle for aerodynamically accepting said cooling air; (b) intermediate regions having a progressively increasing cross-sectional area for decelerating and diffusing said cooling air; and (c) exit regions between said vanes, wherein said curved inner surfaces are generally aligned in serial flow relationship with holes provided in said turbine shaft for aerodynami cally directing said cooling air into said turbine shaft.

7. Apparatus substantially as hereinbefore described with reference to and as illustrated in Fig. 3 or Fig. 4 of the drawings.