Abstract:
The present invention relates to a device for ventilating turbine components in a gas turbine engine comprising two turbine rotors mechanically independent of each other, each with at least one turbine disk, an HP turbine disk and an LP turbine disk respectively, and with a first circuit for ventilating the LP turbine. The device comprises an air compression wheel arranged downstream of the HP turbine disk especially between said two turbine disks, HP and LP in order to assist the circulation of the air in said first circuit. The invention also relates to the wheel.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to the field of gas turbine engines and focuses on the circulation of the air required for the ventilation and cooling of components located downstream of the combustion chamber, especially the turbine disks.  
         [0002]     In a gas turbine engine, it is necessary to make air circulate through all the components subject to thermal stresses from hot gases downstream of the combustion chamber in order to control their temperature. In a two-cylinder engine, the air circuit for the ventilation of the high pressure section is distinct from the one for ventilating the low pressure section located downstream, because the materials and the thermal stresses are different  
         [0003]     The present invention relates to the low pressure section ventilation circuit.  
       DESCRIPTION OF THE PRIOR ART  
       [0004]     In a modem two-cylinder engine for civilian use, such as the CFM engine, comprising a high-pressure (HP) cylinder with an HP turbine stage  1  and a low-pressure (LP) cylinder with an LP turbine  30  with three stages  31 ,  32  and  33 , the various circuits providing ventilation downstream of the high-pressure turbine are illustrated in  FIG. 1 ; the following items can be seen:  
         [0005]     An air flow A, drawn off from the center of the HP compressor, routed through the vanes of the distributor  20  of the first LP stage and providing at A′ the purging of the downstream cavity  11  of the HP turbine  10 .  
         [0006]     A fraction A″ of this same flow providing the ventilation of the passages in the first two fans of stages  31  and  32  of the low-pressure turbine  30 .  
         [0007]     An air flow B drawn off upstream of the HP compressor, routed through the passage  13  in the HP turbine  10  and providing the ventilation of the passage in the third stage  33  of the LP turbine  30 .  
         [0008]     An air flow C drawn off at the LP compressor, routed through the passage  13  in the HP turbine  10 , and providing the pressurization of the covers  36  of the chambers containing the bearings.  
         [0009]     Compressors for this type of engine are axial and have sufficient spaces for guiding the various ventilation air flows from the draw-off zone to where they are used.  
         [0010]     Some engines that are less powerful and more compact have an HP cylinder with a shorter radial compressor, and their compression ratio is lower. This arrangement poses problems when it comes to providing the ventilation function mentioned above.  
         [0011]     The pressure is not always sufficient to ventilate the passages in the LP turbine disks correctly, and this situation is not helped by the small cross section of flow between the passage in the HP turbine and the LP shaft.  
         [0012]     The radial compressor centrifugal wheel has a relatively large output diameter. This results in a reduced gap for the air routed to the LP turbine first stage distributor. In addition, as shown in  FIG. 2 , the draw-off within the HP compressor is often carried out by means of centripetal draw-off tubes which cause a large pressure drop in the ventilation air.  
         [0013]     The objective of the invention is to solve the abovementioned problems, by providing a means for correctly ventilating the LP turbine disks, especially in compact engines having a centrifugal compressor, which also takes into account the specific dimensional constraints for this type of engine.  
       SUMMARY OF THE INVENTION  
       [0014]     The invention manages to achieve this objective by means of a device for ventilating turbine components in a gas turbine engine comprising two turbine rotors that are mechanically independent of each other, each one with at least one turbine disk, an HP turbine disk and an LP turbine disk respectively, and with a first circuit for ventilating the LP turbine. This device is noteworthy in that it comprises an air compression wheel arranged downstream of the HP turbine disk, in particular between said two, HP and LP, turbine disks assisting at least partially the circulation of air in said first air circuit. More particularly, the air inlet of the wheel connects with the passage in the Up turbine disk, and the passage is supplied with air coming from the HP compressor.  
         [0015]     Owing to the invention, the air circuits through the turbine passages are used efficiently, and it is now also possible to simplify the structure of the first stage distributor of the low-pressure turbine because it is no longer necessary to route air from it through the vanes.  
         [0016]     According to a first embodiment, the compression wheel is connected to the HP turbine disk. Advantageously, the wheel then becomes a structural member of the turbine disk by forming the bearing support. According to a second embodiment the compression wheel is connected to the LP turbine disk.  
         [0017]     According to another feature, the compression wheel comprises a disk provided with radial vanes cooperating with a stator baffle in order to compress the air. Advantageously, the baffle includes air guide vanes.  
         [0018]     According to another feature, the stator baffle delimits with the HP turbine disk an HP turbine downstream cavity, and the air coming from the HP turbine disk passage partly supplies the wheel and partly supplies the cavity.  
         [0019]     According to another feature, the device comprises a second ventilation circuit, said circuit ventilating the separate bearing oil chamber covers, in particular said second circuit comprises a part forming a guide channel that is coaxial with the guide part of the first circuit.  
         [0020]     The invention also relates to an air compression wheel for the device comprising a radial plate with a first annular portion provided with mounting holes and a second portion provided with radial vanes. According to a first embodiment, the first portion is radially inside in relation to the second portion. According to a second embodiment, the first portion is radially outside in relation to the second portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The description which follows relates to two non-limiting embodiments of the invention, with reference to the appended drawings, in which:  
         [0022]      FIG. 1  illustrates in half axial cross section part of a state-of-the-art two-cylinder gas turbine engine, comprising an HP turbine and an LP turbine;  
         [0023]      FIG. 2  illustrates in half axial cross section an engine with a radial compressor from the prior art;  
         [0024]      FIG. 3  illustrates in half axial cross section a turbine disk fitted with a wheel according to the invention;  
         [0025]      FIG. 4  illustrates in perspective view a single wheel according to the invention; and  
         [0026]      FIG. 5  illustrates a second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Referring to  FIG. 2 , it shows what is known as a “small” two-cylinder gas turbine engine. The high-pressure (HP) cylinder comprises a turbine  110  connected to an HP compressor  115  by a shaft  117 . The compressor  115  is of the centrifugal wheel type. The low-pressure cylinder comprises a low-pressure turbine  120  with several stages mounted on a shaft  127 , coaxial with the shaft  117 , being connected to an axial-type low-pressure compressor  125 , itself having several stages. A combustion chamber  130  is arranged between the compressor and the BP cylinder turbine. A distributor stage  140  separates the two turbines  110  and  120 .  
         [0028]     As can be seen on this figure without the use of the invention, a first ventilation air circuit E comprises an air inlet upstream of the HP compressor and this air is directed axially between the two shafts  117  and  127  through the passage in the turbine rotor  110  in order to ventilate the downstream cavity of the turbine. A second air circuit is guided between the outer casing  150  of the engine and HP cylinder housing via tubes that are not shown. It appears that such an arrangement is not satisfactory because the quantity of air supplying the ventilation circuits is not sufficient. 
        With regard to the first circuit, the flow area between the shafts  117  and  127  is too small for the ventilation air.     With regard to the second circuit, there is little space for installing ventilation tubes on the housing.        
 
         [0031]     According to the invention, there has been arranged, downstream of the HP turbine disk, an air compression wheel for ventilating the LP turbine. Such a device is illustrated in  FIG. 3 .  
         [0032]     All that can be seen in this figure is the disk  210 D of the HP turbine  210  with a central passage  210 A. The disk  210 D is connected to the shaft  217 . At its upstream end, the shaft  217  is connected to the compressor, which is not visible in the figure. The disk carries HP turbine vanes  210 T receiving the hot gases from the combustion chamber not visible in the figure.  
         [0033]     A distributor stator stage  220  is placed downstream of the HP turbine  210  immediately upstream of the vanes of the low-pressure LP turbine  230 .  
         [0034]     This turbine is composed of several disks connected together, of which only the first two,  231  and  232 , can be seen. The turbine  230  is carried on a shaft  237 . This shaft  237  is concentric with the shaft  217 . A downstream inter-shaft bearing  240  holds the two concentric shafts and allows them to rotate freely in relation to each other. The upstream bearing is not visible in the figure, the same as the downstream bearing carrying the shaft  237  in the fixed structure. An annular space F is thus arranged between the passage  210 A of the turbine disk and the shaft  217 . Another annular space G is also arranged between the two shafts  217  and  237 .  
         [0035]     The disk  210 D has a flange  210 B to which is bolted a compression wheel  300 . The wheel has a part generally in the form of a disk at right-angles to the engine&#39;s axis, with a first portion  301  drilled axially with a series of holes  303  for mounting bolts  303 ′ to pass through for fastening the wheel to the flange  210 B. Radially on the outside of this portion, the disk has an annular portion  305  provided with radial vanes  307 . This second portion cooperates with a fixed wall  222  to form a centrifugal air compressing means with an axial inlet and a radial outlet. The wall  222  carries axial compressor inlet guide vanes  222 A and radial compressor outlet guide vanes  222 S. An annular deflector  222 D directs the air flow exiting the compressor toward the base of the turbine disks  231  and  232 . The wall  222  makes with the turbine disk  210 D a space  211  forming said HP turbine downstream cavity, and a labyrinth sealing means  222 L cooperates with a corresponding means  210 L on the disk in order to confine the air in this cavity  211 . Note that the wheel comprises a cylindrical portion  309  forming a support for the outer race  242  of the bearing  240 . The bearing elements  244  are thereby arranged between the inner race  246  connected to the shaft  237  and the outer race  242  connected to the shaft  217  and form the inter-shaft bearing  240 .  
         [0036]     The flange  210 B is at right-angles to a cylindrical axial part  210 B 1  and a perpendicular part  210 B 2  comprising the holes, cooperating with the holes  303  for the bolts  303 ′ to pass through. The cylindrical part  210 B 1  is drilled with radial holes  210 B 1   r . An annular space is arranged between the flange  210 B, the wheel  300  and the wall  222 . Radial holes  222 P are made in the wall  222  between the vanes  222 A and the seal  222 L.  
         [0037]     Holes  309 P are made in the cylindrical portion  309  of the wheel in order to connect the space G with the downstream part of the low-pressure rotor  230 .  
         [0038]     The inventive device operates in the following manner. When the engine is operating, the two rotors, HP and LP respectively, are driven by the gases coming from the combustion chamber. Each one turns independently of the other. The ventilation air drawn off at the final stages of the upstream compressor according to a first circuit is guided into the space F, and passes through the flange  210 B via the holes  21 OB 1   r . A part is aspirated by the wheel  300 , and the other part is guided through the holes  222 P into the downstream cavity  211  of the HP turbine that it ventilates. The compressed air in the compression channels of the wheel  300  is evacuated in the direction of the turbine disks  231  and  232  for which it provides the ventilation, and is evacuated into the combustion gas stream or via the appropriate orifices through the LP turbine support  230 .  
         [0039]     The ventilation air, drawn off at the primary stages of the HP compressor, which circulates in the annular space G, between the two shafts  217  and  237 , is guided through the holes  309 P toward the downstream of the LP turbine, in particular toward the bearing oil chamber covers.  
         [0040]     According to another embodiment, illustrated in  FIG. 5 , there is the HP turbine disk  210 ′ with a downstream flange  210 B′, for mounting a labyrinth sealing member  210 L′. The wheel  400  is here connected to the LP turbine disk  231 ′ by which it is driven. The wheel  400  as in the preceding solution cooperates with the stator member  222 ′ to form compression channels for the air which is guided through the central passage of the disk  210 D′, the holes  210 P′ made in the flange  210 B′ and coming from the upstream compressor. The air flow is split into a part which purges the downstream cavity  211 ′ of the turbine disk  210 ′ and a part which is drawn into the compression channels of the wheel  400 . The wheel  400  comprises openings for ventilating the turbine disks  231 ′ and  233 ′.