Patent Publication Number: US-6210104-B1

Title: Removal of cooling air on the suction side of a diffuser vane of a radial compressor stage of gas turbines

Description:
FIELD OF THE INVENTION 
     The present invention pertains to the removal of cooling air from the diffuser part of a radial stage of a compressor of a gas turbine. 
     BACKGROUND OF THE INVENTION 
     In a gas turbine, which comprises a compressor, a combustion means and a turbine, cooling air, which is removed from the compressor under high pressure, is needed to cool the components that come into contact with hot gas. 
     In a gas turbine developed by the applicant, compressed air is removed from a radial stage of a compressor, which is an end stage in this case, through the suction-side side wall of the diffuser vane. 
     The compressed cooling air is removed from the compressor stage, which comprises a rotor disk and a diffuser, and is fed to a cooling air line arranged in the housing of the compressor. A deadwater or separation area, which compromises the efficiency of the entire compressor stage, frequently develops in such a diffuser in the suction-side, rear area of the flow channel due to the buildup of boundary layers on the diffuser vanes. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The primary object of the present invention is to design the removal of cooling air in the compressor part of a gas turbine such that favorable effects on the compressor efficiency are generated from a fluidic viewpoint. 
     According to the invention, removal of cooling air from the diffuser part of a radial stage of a compressor of a gas turbine is provided with at least one opening arranged in the horizontal blind holes on the suction side of the diffuser blading. Cooling air holes are led through the diffuser housing outside and they are connected to the cooling air discharge. 
     The openings may be designed as round openings. The openings may also be designed as slots. 
     The removal of cooling air is brought about by the device according to the present invention such that the compressed cooling air is removed through openings or slots from horizontally extending holes within the diffuser vane on the suction side of the diffuser vanes. 
     These horizontally arranged holes of the diffuser vanes are connected by analogous holes of the same type in the outside of the diffuser to the cooling air discharge in the compressor housing, so that the compressed cooling air is fed from the diffuser directly to the outside air channel. The boundary layer is thus drawn off on the suction side of the diffuser vanes. As a result, a deadwater area is prevented from forming or it is at least greatly reduced, which increases the efficiency of the entire stage. 
     On the whole, a deadwater area is avoided by the device according to the present invention, which leads to a reduction of the losses in the diffuser and to an increase in the efficiency of the stage. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a schematic longitudinal sectional view through the compressor part of a gas turbine in the area of the diffuser; 
     FIG. 2 is an enlarged view of the diffuser from FIG. 1 with various exemplary embodiments of the removal of cooling air, and 
     FIG. 3 is a cross section of the diffuser vane. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular, FIG. 1 shows a longitudinal section through a compressor of a gas turbine with parts of the annular space  8 , the vane support interior space  9 , the compressor housing  15  and the discharge opening  16  for the compressed air, which is then fed to the combustion chamber. The rotor blades  12  of the compressor are fastened to the rotor disks  13 , which are held together by a plurality of tie rods  14 . Guide vanes  11  are fastened in the vane support  1 . The end stage of the compressor comprises a radial stage with a radial rotor disk  2 , a bladed diffuser  3  and an axial guide vane  18 . The compressed air then enters the annular space  8 . The diffuser  20  comprises the housing-side inner part  20 . 1  and the diffuser housing outside part  20 . 2  as well as the diffuser vanes  3  with inner horizontal blind holes  19 . 
     In such a gas turbine, which comprises a compressor, a combustion means and a turbine, cooling air, which is taken from the compressor under high pressure, is needed to cool the components that come into contact with hot gas. 
     FIG. 2 shows an enlarged view of the diffuser from FIG.  1 . The diffuser blading  3  is used at the same time, with corresponding fastening elements  7 , to connect the vane support  1  to the rear bearing housing  21 . Compressed cooling air can be removed through both round openings  6 . 1  and slots  6 . 2 , which are milled into the diffuser vane  3 . Through the removal openings  6 . 1 ,  6 . 2 , the cooling air enters the blind holes  19  of the diffuser vane  3  and then further, through holes  19 . 1  in the diffuser housing outside part  20 . 2 , the cooling air discharge  10  arranged in the compressor housing. 
     FIG. 3 shows a cross section through the diffuser  20  when viewed in the direction of the diffuser housing inside  20 . 1  with radially arranged diffuser vanes  3  with the cooling air discharges at the blind holes  19 , which may be designed as holes  6 . 1  or slots  6 . 2 . A deadwater area  5 , indicated by broken lines in the right-hand part of FIG. 3, which reduces the efficiency of the entire compressor stage, cannot develop any more in this diffuser  20  in the suction-side, rear area of the flow channel. 
     The removal of cooling air is designed such that the cooling air is removed on the suction side of the diffuser vane  3  through suitable removal openings  6 . 1 / 6 . 2  in horizontally extending blind holes  19  and is fed through holes in the diffuser housing outside  20 . 2  and via the cooling air discharge in the housing to the components of the gas turbine that come into contact with the hot gas. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.