Turbine bucket assembly and turbine system

Abstract

A turbine bucket assembly and turbine system are disclosed. The assembly includes a multi-lobe joint having an integral platform, the joint having a first axial length; a segmented airfoil having a root segment extending radially outward from the platform and a tip segment coupled to the root segment, the tip segment having a second axial length less than the first axial length; and a turbine wheel defining a receptacle with a geometry corresponding to the multi-lobe joint and being coupled to the multi-lobe joint. A tip segment material, a root segment material, and a turbine wheel material are selected, such that the turbine wheel material and the root segment material have a lower heat resistance and a higher thermal expansion than the tip segment material.

What is claimed is: 
     
         1 . A turbine bucket assembly, comprising:
 a multi-lobe joint having an integral platform, the joint having a first axial length;   a segmented airfoil having a root segment extending radially outward from the integral platform and a tip segment coupled to the root segment, the tip segment having a second axial length, the second axial length being less than the first axial length; and   a turbine wheel defining a receptacle with a geometry corresponding to the multi-lobe joint and being coupled to the multi-lobe joint;   wherein the tip segment includes a tip segment material, the root segment includes a root segment material, and the turbine wheel includes a turbine wheel material, the turbine wheel material and the root segment material having a lower heat resistance and a higher thermal expansion than the tip segment material.   
     
     
         2 . The assembly of  claim 1 , wherein the tip segment material is a titanium aluminide. 
     
     
         3 . The assembly of  claim 1 , wherein the root segment material is a superalloy. 
     
     
         4 . The assembly of  claim 1 , wherein the turbine wheel material is a superalloy. 
     
     
         5 . The assembly of  claim 1 , wherein the root segment material is a superalloy different from the turbine wheel material superalloy. 
     
     
         6 . The assembly of  claim 1 , further comprising a tip shroud integrally positioned on the tip segment of the segmented airfoil. 
     
     
         7 . The assembly of  claim 6 , wherein the tip shroud comprises a sealing rail positioned on an outer surface of the tip shroud distal from the multi-lobe joint. 
     
     
         8 . The assembly of  claim 1 , wherein the multi-lobe joint is removably coupled to the turbine wheel by an axial joint, a circumferential joint, a dovetail joint, a dado joint, a box joint, a tongue-and-groove joint, or a combination thereof. 
     
     
         9 . The assembly of  claim 1 , wherein the geometry of the turbine wheel corresponding to the multi-lobe joint defines a rim of the turbine wheel. 
     
     
         10 . The assembly of  claim 1 , further comprising an impact strip positioned on a leading edge of the segmented airfoil. 
     
     
         11 . The assembly of  claim 1 , further comprising an impact strip positioned on a trailing edge of the segmented airfoil. 
     
     
         12 . The assembly of  claim 1 , wherein the root segment is removably coupled to the tip segment by a single-lobe segment joint, the single-lobe segment joint being an axial joint, a circumferential joint, a curved dovetail joint, a dado joint, a box joint, a tongue-and-groove joint, or a combination thereof. 
     
     
         13 . The assembly of  claim 1 , further comprising a damper removably coupled to the root segment. 
     
     
         14 . A turbine bucket assembly, comprising:
 a multi-lobe joint having an integral platform, the joint having a first axial length;   a segmented airfoil having a root segment extending radially outward from the integral platform and a tip segment coupled to the root segment, the tip segment having a second axial length, the second axial length being less than the first axial length; and   a turbine wheel having a receptacle with a geometry corresponding to the multi-lobe joint and being coupled to the multi-lobe joint;   wherein the tip segment includes a tip segment material, the root segment includes a root segment material, and the turbine wheel includes a turbine wheel material, the tip segment material being a titanium aluminide, the root segment material being a first superalloy, and the turbine wheel material being a second superalloy.   
     
     
         15 . The turbine bucket assembly of  claim 14 , wherein the first superalloy and the second superalloy are one of a nickel-based superalloy, a cobalt-based superalloy, and a steel-based superalloy. 
     
     
         16 . A gas turbine system, comprising:
 a compressor section;   a combustor section configured to receive air from the compressor section; and   a turbine section in fluid communication with the combustor section, the turbine section comprising a stator and a turbine bucket assembly, the turbine bucket assembly comprising:
 a multi-lobe joint having an integral platform, the joint having a first axial length; 
 a segmented airfoil having a root segment extending radially outward from the integral platform and a tip segment coupled to the root segment, the tip segment having a second axial length, the second axial length being less than the first axial length; and 
 a turbine wheel having a receptacle with a geometry corresponding to the multi-lobe joint and being coupled to the multi-lobe joint; 
 wherein the tip segment includes a tip segment material, the root segment includes a root segment material, and the turbine wheel includes a turbine wheel material, the turbine wheel material and the root segment material having a lower heat resistance and a higher thermal expansion than the tip segment material. 
   
     
     
         17 . The gas turbine system of  claim 16 , further comprising a plurality of axially spaced stages of turbine bucket assemblies including a last stage of turbine bucket assemblies. 
     
     
         18 . The gas turbine system of  claim 17 , wherein the segmented airfoil has a leading edge and a trailing edge, and further comprises at least one impact strip attached to at least one of the leading edge, the trailing edge, the tip segment, and the root segment. 
     
     
         19 . The gas turbine system of  claim 18 , wherein impact strips are attached to the leading edge of the tip segments of the plurality of turbine bucket assemblies in one or more of the plurality of turbine stages. 
     
     
         20 . The gas turbine system of  claim 18 , wherein impact strips are attached to the trailing edge of the tip segments of the plurality of turbine bucket assemblies in one or more of the plurality of turbine stages with the exception of the last stage.