Combustor exit duct for gas turbine engines

Abstract

A gas turbine engine combustor includes an exit duct having annular first and second exit duct walls radially spaced apart to define therebetween the combustor exit opening. The first and/or second exit duct walls has a double-skin wall section which includes an inner hot wall facing the combustor exit opening and an outer cold wall fastened to the inner hot wall and radially spaced away therefrom to define a radial gap therebetween. The outer cold wall has a coefficient of thermal expansion greater than that of the inner hot wall. This helps reduce thermal growth mismatch between the outer cold wall and the inner hot wall during operation of the combustor, and reduces thermal stress at the joint between the hot and cold walls.

1 . A gas turbine engine combustor comprising outer and inner annular liners and an exit duct at a downstream end, the exit duct circumscribing an annular combustor exit opening defining a combustion gas path therethrough, the exit duct including annular first and second exit duct walls radially spaced apart to define therebetween the combustor exit opening, at least one of the first and second exit duct walls having a double-skin wall section at a most downstream end thereof, the double-skin wall section including an inner hot wall facing said combustor exit opening and an outer cold wall radially spaced away from the hot wall to define a radial gap therebetween, the outer cold wall being disposed outside of said combustion gas path, the inner hot wall and the outer cold wall being fastened together by at least one joint therebetween, the outer cold wall having a coefficient of thermal expansion greater than that of the inner hot wall to reducing thermal growth mismatch between the outer cold wall and the inner hot wall during operation of the combustor and reduce thermal stress at the joint. 
     
     
         2 . The gas turbine engine combustor as defined in  claim 1 , wherein the combustor is a reverse flow combustor, the first and second exit duct walls respectively comprising a large exit duct portion and a small exit duct portion. 
     
     
         3 . The gas turbine engine combustor as defined in  claim 2 , wherein both the large exit duct portion and the small exit duct portion comprise said double-skin wall section at the most downstream ends thereof. 
     
     
         4 . The gas turbine engine combustor as defined in  claim 3 , wherein the inner hot wall and the outer cold wall of the short exit duct comprise spaced apart curved wall portions, a radius of curvature of the inner hot wall being different from that of the outer cold wall. 
     
     
         5 . The gas turbine engine combustor as defined in  claim 1 , wherein the joint between the inner hot wall and the outer cold wall includes a welded joint disposed upstream of an exit end of the double-skin wall section. 
     
     
         6 . The gas turbine engine combustor as defined in  claim 5 , wherein said welded joint is disposed at an upstream end of the combustor exit duct in a transition area of the combustor disposed between the outer and inner annular liners and the exit duct. 
     
     
         7 . The gas turbine engine combustor as defined in  claim 1 , wherein the outer cold wall of the double-skin wall section includes an annular flange wall being formed from a formable metal sheet of a type compatible for welding to the inner hot wall. 
     
     
         8 . The gas turbine engine combustor as defined in  claim 1 , wherein both the inner hot wall and the outer cold wall are made of sheet metal. 
     
     
         9 . The gas turbine engine combustor as defined in  claim 1 , wherein outer cold wall is formed of Hastalloy X™. 
     
     
         10 . The gas turbine engine combustor as defined in  claim 1 , wherein the inner hot wall is formed of one of IN625, Haynes 188 and Haynes 230. 
     
     
         11 . The gas turbine engine combustor as defined in  claim 1 , wherein at least the outer cold wall of said double-skin wall section includes one or more impingement cooling holes therein. 
     
     
         12 . A combustor exit duct for a gas turbine engine, the combustor exit duct comprising annular first and second exit duct walls radially spaced apart to define therebetween a combustor exit opening, at least one of the first and second exit duct walls having a double-skin wall section at a most downstream end thereof, the double-skin wall section including an inner hot wall facing said combustor exit opening and an outer cold wall radially spaced away from the hot wall to define a radial gap therebetween, the outer cold wall being disposed outside of said combustion gas path, the inner hot wall and the outer cold wall being fastened together by at least one joint therebetween, the outer cold wall having a coefficient of thermal expansion greater than that of the inner hot wall to reducing thermal growth mismatch between the outer cold wall and the inner hot wall during operation of the combustor and reduce thermal stress at the joint. 
     
     
         13 . The combustor exit duct as defined in  claim 12 , wherein both the first and second exit duct walls comprise said double-skin wall section at the most downstream ends thereof. 
     
     
         14 . The combustor exit duct as defined in  claim 12 , wherein the joint between the inner hot wall and the outer cold wall includes a welded joint disposed upstream of an exit end of the double-skin wall section. 
     
     
         15 . The combustor exit duct as defined in  claim 12 , wherein the outer cold wall of the double-skin wall section includes an annular flange formed from a formable metal sheet of a type compatible for welding to the inner hot wall. 
     
     
         16 . The combustor exit duct as defined in  claim 12 , wherein both the inner hot wall and the outer cold wall are made of sheet metal. 
     
     
         17 . The combustor exit duct as defined in  claim 12 , wherein outer cold wall is formed of Hastalloy X™, and the inner hot wall is formed from one of IN625, Haynes 188 and Haynes 230. 
     
     
         18 . The combustor exit duct as defined in  claim 12 , wherein at least the outer cold wall of said double-skin wall section includes one or more impingement cooling holes therein. 
     
     
         19 . A method of forming a gas turbine engine combustor, the combustor having outer and inner annular liners and an exit duct at a downstream end, the method comprising: providing a first and a second annular wall of the exit duct which circumscribe an annular combustor exit opening defining a combustion gas path therethrough; forming a double-skin wall section on at least one of the first and second annular walls of the exit duct, by welding an annular outer cold wall flange to an inner hot wall portion facing said combustor exit opening to form an annular welded joint therebetween, the annular outer cold wall flange being spaced apart from the inner hot wall downstream of said welded joint to define a radial gap therebetween at a downstream end of the double-skin wall section; and reducing thermal stress at the welded joint between the outer cold wall flange and the inner hot wall of the double-skin wall section by forming the outer cold wall flange from a material having a coefficient of thermal expansion that is greater than that of the inner hot wall to thereby reducing thermal growth mismatch between the outer cold wall flange and the inner hot wall. 
     
     
         20 . The method as claimed in  claim 19 , further comprising forming both the inner hot wall and the outer cold wall flange with a curved portion, the curved portion of the annular outer cold wall flange having a different radius of curvature than that of the inner hot wall.