Apparatus and methods for cooling turbine bucket platforms

Abstract

A turbine bucket includes a platform interfacing between an airfoil and a shank. The platform is provided with a plurality of cavities covered by impingement cooling plates along the platform underside. Purge air supplied in the gaps between adjacent buckets flows through holes in the impingement plates to impingement cool opposite wall portions of the platform. The cooling air in the cavities is transmitted through film cooling holes in the platform to form a thin film of insulating air along the surface of the platform exposed to the hot gas in the hot gas path.

1 . A turbine bucket having an airfoil, a shank, and a platform at an interface between the bucket shank and the bucket airfoil, said platform including at least one cavity closed by an impingement plate along an underside of said platform and spaced from an opposite wall portion of said platform, said opposite wall portion having a surface exposed to and in part defining a hot gas flow path through the turbine, said impingement plate including a plurality of impingement cooling holes for directing a cooling medium through said holes into said cavity and toward said opposite wall portion to impingement cool said platform, and a plurality of holes through said wall portion in communication with the cooling medium within said cavity for film cooling the platform surface exposed along the hot gas flow path.  
   
   
       2 . A turbine bucket according to  claim 1  wherein said cavity is located in said platform adjacent a pressure side of said bucket.  
   
   
       3 . A turbine bucket according to  claim 1  wherein said cavity is located in said platform adjacent a suction side of said bucket.  
   
   
       4 . A turbine bucket according to  claim 1  including a second cavity within the platform closed by a second impingement plate along an underside of said platform and spaced from a second opposite wall portion of said platform, said second opposite wall portion having a second surface exposed to and in part defining the hot gas flow path through the turbine, said second impingement plate including a plurality of impingement cooling holes for directing a cooling medium through said holes thereof into said second cavity and toward said second opposite wall portion to impingement cool said platform, and a plurality of holes through said second wall portion in communication with the cooling medium within said second cavity for film cooling the second platform surface exposed along the hot gas flow path.  
   
   
       5 . A bucket according to  claim 4  wherein said first and second cavities are located in said platform adjacent a suction side of said bucket airfoil.  
   
   
       6 . A bucket according to  claim 4  wherein said first and second cavities are located in said platform adjacent respective suction and pressure sides of said bucket airfoil.  
   
   
       7 . A turbine bucket according to  claim 1  including second and third cavities within the platform closed by said second and third impingement plates along an underside of said platform and spaced from opposite second and third wall portions of said platform, said second and third opposite wall portions having respective surfaces exposed to and in part defining the hot gas flow path through the turbine, said second and third impingement plates including a plurality of impingement cooling holes for directing a cooling medium through said holes into said second and third cavities, respectively, and toward said second and third opposite wall portions to impingement cool said platform and a plurality of holes through said second and third wall portions in communication with the cooling medium within said second and third cavities for film cooling the respective platform surfaces exposed along the hot gas flow path.  
   
   
       8 . A turbine bucket according to  claim 7  wherein said one cavity is located in said platform adjacent a pressure side of said bucket airfoil and said second and third cavities are located in said platform adjacent a suction side of said bucket airfoil.  
   
   
       9 . A method of cooling a platform of a turbine bucket comprising the steps of: 
 (a) providing a cavity within the platform;    (b) closing the cavity by securing an impingement plate along an underside of the platform spaced from an opposite wall portion of the platform, said opposite wall portion having a surface exposed to and in part defining a hot gas flow path through the turbine;    (c) flowing a cooling medium through cooling holes formed in the impingement plate into said cavity and directing the cooling medium towards said opposite wall portion to impingement cool said platform; and    (d) passing the cooling medium within said cavity through film cooling holes in said wall portion to film cool the surface of the platform along the hot gas flow path.    
   
   
       10 . A method according to  claim 9  including providing said cavity within the platform adjacent a pressure side of the bucket airfoil.  
   
   
       11 . A method according to  claim 9  including providing said cavity within the platform adjacent a suction side of the bucket airfoil.  
   
   
       12 . A method according to  claim 9  including providing a second cavity within the platform, closing the second cavity by securing a second impingement plate along an underside of the platform spaced from a second opposite wall portion of the platform, said second opposite wall portion in part defining the hot gas flow path through the turbine, flowing the cooling medium through cooling holes formed in the second impingement plate into said second cavity and directing the cooling medium toward said second opposite wall portion to impingement cool said platform, and passing the cooling medium within said second cavity through film cooling holes in said opposite wall portion of said second cavity to film cool the surface of the platform exposed along the hot gas flow path.  
   
   
       13 . A method according to  claim 12  including providing the first and second cavities in said platform adjacent respective pressure and suction sides of said bucket airfoil.  
   
   
       14 . A method according to  claim 12  including providing said first and second cavities in said platform adjacent respective pressure and suction sides of said bucket airfoil.  
   
   
       15 . A method according to  claim 9  including providing second and third cavities within the platform, closing the second and third cavities by securing respective second and third impingement plates along an underside of the platform spaced from second and third opposite wall portions of the platform, said second and third opposite wall portions have respective second and third surfaces exposed to and in part defining the hot gas flow path through the turbine, flowing cooling medium through the cooling holes formed in the second and third impingement plates into said second and third cavities and directing the cooling medium toward said second and third opposite wall portions, respectively, to convectively cool said platform, and passing the cooling medium within said second and third cavities through film cooling holes in said second and third opposite wall portions, respectively, to film cool the surfaces of the platform exposed to the hot gas flow path.