Systems and apparatus relating to diffusers in combustion turbine engines

Abstract

A discharge diffuser that includes: a forward section and a dump cavity, the forward section being configured to direct discharge from the compressor to the dump cavity; an inner diffuser wall that defines an inner radial flowpath of the upstream section; and an outer diffuser wall that defines an outer radial flowpath of the upstream section; wherein at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step.

1 . A discharge diffuser in a combustion turbine engine that includes a compressor, a combustor and a turbine, the discharge diffuser comprising:
 a forward section and a dump cavity, the forward section being configured to direct discharge from the compressor to the dump cavity;   an inner diffuser wall that defines an inner radial flowpath of the upstream section; and   an outer diffuser wall that defines an outer radial flowpath of the upstream section;   wherein at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step.   
     
     
         2 . The discharge diffuser according to  claim 1 , wherein the outer diffuser wall flares outwardly such that the inner diffuser wall and the outer diffuser wall define a widening flowpath, and the aft lip comprises the downstream termination point of the inner diffuser wall. 
     
     
         3 . The discharge diffuser according to  claim 2 , wherein the dump cavity comprises a region of increased volume positioned downstream of the flared inner and outer diffuser walls of the upstream section, and wherein the dump cavity is configured to surround at least a portion of the combustor. 
     
     
         4 . The discharge diffuser according to  claim 1 , wherein the overhanging step comprises a step wall that extends from the aft lip of the forward section to an inner cavity wall of the dump cavity, the inner cavity wall comprising an inner radial boundary of the dump cavity. 
     
     
         5 . The discharge diffuser according to  claim 4 , wherein the step wall comprises a radial step that, from a beginning point at the aft lip of the inner diffuser wall, slants in a direction that includes both an inboard directional component and an axial-upstream directional component. 
     
     
         6 . The discharge diffuser according to  claim 4 , wherein the overhanging step comprises a radial step that, from the aft lip, slants radially inward and in an upstream direction so that the radial step undercuts a portion of the inner diffuser wall. 
     
     
         7 . The discharge diffuser according to  claim 1 , wherein:
 the dump cavity comprises an inner cavity wall that defines an inner radial boundary of the dump cavity; and   the overhanging step includes a step wall that connects the inner diffuser wall to the inner cavity wall.   
     
     
         8 . The discharge diffuser according to  claim 7 , wherein the inner cavity wall comprises a position that is inboard in relation to the inner diffuser wall; and
 wherein the radial height of the overhanging step comprises the distance by which the inner cavity wall is inboard of the inner diffuser wall.   
     
     
         9 . The discharge diffuser according to  claim 8 , wherein the step wall, at one end, connects to the inner diffuser wall at the aft lip and, at the other end, connects to the inner cavity wall at a dump cavity forward edge. 
     
     
         10 . The discharge diffuser according to  claim 9 , wherein the overhanging step is configured such that the aft lip comprises an axial position that is aft relative to the axial position of the dump cavity forward edge. 
     
     
         11 . The discharge diffuser according to  claim 10 , wherein:
 the step wall comprises a substantially planar shape;   a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and   the overhanging step is configured such that the step wall angle comprises a range of between 20 and 60 degrees.   
     
     
         12 . The discharge diffuser according to  claim 10 , wherein:
 the step wall comprises a substantially planar shape;   a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and   the overhanging step is configured such that the step wall angle comprises a range of between 30 and 50 degrees.   
     
     
         13 . The discharge diffuser according to  claim 10 , wherein:
 the step wall comprises a substantially planar shape;   a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and   the overhanging step is configured such that the step wall angle comprises approximately 40 degrees.   
     
     
         14 . The discharge diffuser according to  claim 10 , wherein the aft lip comprises one of a rounded edge, a sharp edge, and a radially aligned flat edge; and wherein the dump cavity forward edge comprises a filleted edge. 
     
     
         15 . The discharge diffuser according to  claim 10 , wherein the radial height of the overhanging step comprises 4 to 6 inches. 
     
     
         16 . The discharge diffuser according to  claim 10 , further comprising a transition step located on the inner diffuser wall;
 wherein the distance between a transition step located on the inner diffuser wall and the aft lip comprises 3.5 to 4.5 inches; and   wherein the radial height of the transition step comprises approximately 0.5 inches.   
     
     
         17 . A discharge diffuser for a combustion turbine engine that includes a compressor, a combustor and a turbine, the discharge diffuser comprising:
 a forward section configured to direct compressor discharge from the compressor to a dump cavity;   wherein:
 the forward section includes an inner diffuser wall and an outer diffuser wall, the outer diffuser wall flaring outwardly to define a widening flowpath therethrough; 
 the dump cavity comprises a region of increased volume positioned downstream of the upstream section, the dump cavity being configured to surround at least a portion of a combustor; and 
 at an aft lip of the inner diffuser wall, the discharge diffuser comprises an overhanging step, the overhanging step including a step wall that, from the aft lip, slants radially inward and in an upstream direction so that the step wall undercuts a portion of the inner diffuser wall. 
   
     
     
         18 . The discharge diffuser according to  claim 17 , wherein:
 the dump cavity comprises an inner dump cavity wall that defines an inner radial boundary of the dump cavity; and   the step wall connects the inner diffuser wall to the inner cavity wall, the inner dump cavity wall comprising a position that is inboard in relation to the inner diffuser wall.   
     
     
         19 . The discharge diffuser according to  claim 18 , wherein:
 the step wall, at one end, connects to the inner diffuser wall at the aft lip and, at the other end, connects to the inner cavity wall at a dump cavity forward edge; and   the overhanging step is configured such that the aft lip comprises an axial position that is aft relative to the axial position of the dump cavity forward edge.   
     
     
         20 . The discharge diffuser according to  claim 18 , wherein:
 the step wall comprises a substantially planar shape;   a step wall angle comprises the angle formed between the plane of the step wall and a radially oriented reference line; and   the overhanging step is configured such that the step wall angle comprises a range of between 30 and 50 degrees.