Patent Publication Number: US-7905706-B1

Title: Turbine blade with spar and shell cooling

Description:
FEDERAL RESEARCH STATEMENT 
     None. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a gas turbine engine, and more specifically to a turbine blade of spar and shell construction with cooling of the shell and the platform. 
     2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     A gas turbine engine includes a compressor to compress air, a combustor to burn the compressed air with a fuel and produce a high temperature gas flow, and a turbine to convert the energy from the high temperature gas flow into mechanical energy used to drive the compressor and, in the case of an aero engine to drive a bypass fan, or in the case of an industrial gas turbine (IGT) engine to drive an electric generator. 
     The efficiency of the engine can be increased by passing a higher temperature gas flow into the turbine. However, the inlet temperature of the turbine is limited to the material properties of the first stage blades and vanes. Higher inlet turbine temperatures can be obtained by a combination of material properties (allowing for higher melting temperatures) and improved airfoil cooling. Since the compressed air used for airfoil cooling is bled off from the compressor, maximizing the amount of cooling while minimizing the amount of cooling air used is a major objective for the engine designer. 
     To allow for higher temperatures, turbine airfoils can be made from a spar and shell construction. U.S. Pat. No. 7,080,971 B2 issued to Wilson et al on Jul. 25, 2006 and entitled COOLED TURBINE SPAR AND SHELL BLADE CONSTRUCTION discloses a prior art turbine blade with a spar and shell, the entire disclosure incorporated herein by reference. The shell is made from a very high temperature resistant material and with thin walls in order to allow for high heat transfer coefficient from the outside surface to the inside for best cooling. The spar functions as a support for the shell and a channel forming member for cooling air. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide for a turbine airfoil with a spar and shell construction with a multiple impingement cooled shell in which the spent cooling air is then sued to cool the platform. 
     The present invention is a turbine blade with a spar and shell construction in which the shell is cooled by impingement cooling air forced against the backside wall of the shell, and the spent air from the impingement cooling is then passed through cooling passage within the platform to provide cooling to the platform. The spent air from the platform is then discharged out as purge air for the fillet regions. 
     The shell is a single piece shell that forms the airfoil surface with ribs extending between the walls to provide support. C-shaped clamps are placed over the ledges formed on the lower shell that clamp the shell to the platform of the spar. The C-shaped clamps have cooling passages formed inside that are used for passing the spent cooling air for platform cooling. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a profile view of the multiple impingement cooled spar and shell blade of the present invention. 
         FIG. 2  shows a sectional view of the spar and shell cooled blade of  FIG. 1 . 
         FIG. 3  shows a detailed view of the shell to spar platform clamp construction of the present invention. 
         FIG. 4  shows a front view of the clamp construction through line A-A in 
         FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a multiple hole impingement cooled spar and shell turbine blade for use in a gas turbine engine. The spar includes a cooling supply passage with impingement holes to provide impingement cooling to the backside wall of the shell. The spent cooling air then flows in a serpentine passage through the blade platform to provide cooling for the platform. The spent cooling air from the platform is then passed out through openings along the fillet to act as purge air and prevent hot gas ingestion and to provide cooling for the fillet region. 
       FIG. 1  shows a profile view of the turbine blade with the spar and shell construction of the present invention. The shell  11  includes the blade tip  12 , the pressure and suction sides, and the leading edge trailing edges formed as a single piece. Also formed on the shell are the lower ledge pieces  13  that extend from the lower end of the shell and spread outward as seen in  FIG. 1  and in detail in  FIG. 3 . The lower edge pieces form a fillet  14  on the airfoil. Micro pin fins or rough surfaces may also be built into the inner surface of the shell  11  to enhance the internal cooling performance. 
     The spar  21  includes a root portion  23  with a fir tree configuration and an internal cooling air supply channel  22  to channel pressurized cooling air from outside the blade. The spar also includes a plurality of impingement cooling holes  24  spaced around the spar at certain locations to provide impingement cooling for the backside wall of the shell. The spar  21  also includes blade platforms that extend outward from both the pressure side and the suction side. The platforms  25  have cooling spent air return channels  26  formed on the top surface that carry cooling air. A clamp attachment  31  is located underneath the platforms  25 , and a clamp having a C-shape  32  is placed over the spar and shell pieces to clamp the platform  25  to the shell lower ledge pieces  13 . The spar  21  also includes tip cooling holes on the tip section of the spar  21 . Local stand-off ribs are located between the top edge of the C-clamp and the lower surface of the shell ledges and form a cooling air passage from the spent air return channels  26  in the platforms  25  to the fillet region of the airfoil. 
       FIG. 2  shows a cross sectional view of the spar and shell construction. The shell  21  includes two ribs  15  that extend between the pressure side wall and the suction side wall and divide the inside into three cavities. A row of exit cooling holes  16  are formed along the trailing edge of the shell. The spar  21  includes three radial extending portions that fit into the shell cavities and form the three impingement cavities  22 . The impingement holes  24  are spaced around the three radial extending portions of the spar  21  at a location close to the inner wall surfaces of the shell  11  to provide for impingement cooling. 
     A detailed view of the interface between the spar and shell in the platform is shown in  FIG. 3 . The spar  21  includes the platform  25  extending outward with the spent air cooling channels  26  located on the top surface. The clamp  32  includes the ribs  33  extending inward to abut against the shell lower edge  13  and form a plurality of parallel flow cooling air channels  26 . The platform  25  includes a dovetail  35  on the lower side that engages with a similar shaped dovetail slot formed in the clamp  32  as seen in the detailed view of  FIG. 4 . The dovetail  35  on the platform and the dovetail slot on the clamp forms the clamp attachment  31  of  FIG. 1 . The spar and shell can be made of different materials and clamped together at the blade platform junction. 
     In operation, cooling air is supplied through the airfoil spar cooling supply holes  22  from outside the blade and through the plurality of impingement holes  24  to be impinged onto the inner surface of the shell  11  to provide backside impingement cooling for the airfoil shell  11 . Cooling air also flows through the tip holes  27  to provide impingement cooling to the underside surface of the tip  12  of the shell  11 . Micro pin fins or rough surfaces may also be built into the inner surface of the shell to enhance the internal cooling performance. The spent cooling air from impingement cooling is then returned to the blade attachment region through the multiple cooling channels  26  which is formed in the airfoil spar structure of the blade platform. The return spent air cooling channels  26  is fixed by the spar edge clamp  32  which is built in around the edge of the blade platform. Cooling air from the airfoil flows through the edge clamp structure (formed by the ribs  33  extending from the clamp  32 ) to provide cooling and purge air for the blade fillet region prior to being discharged around the blade root fillet section. A portion of the spent cooling air from the impingement holes  24  is channeled through the airfoil trailing edge exit holes  16  formed in the shell  11 . The pressurized cooling air supplied to the root  23  (the root can have three separate channels to connect the outside source of cooling air to the three cavities  22  formed by the spar) of the spar flows into the three supply passages  22  and then through the impingement holes located on the sides or the tip to provide for impingement cooling of the inner wall surface of the shell on the airfoil sides and the airfoil tip. The impingement cooling air is then collected in the spent air cooling channel formed between the spar and the shell and channeled to the bottom of the shell and spar where the platform and the lower ledge of the shell abut together. The C-clamp holds the spar and shell together, and also acts to direct the spend cooling air from the channel  26  into the channels formed between the ribs  33  of the C-clamp  32 .