Turbine case reinforcement in a gas turbine jet engine

Abstract

In one embodiment, a low or high pressure turbine case is machined on its outside surface to form circumferential notches. The notches may coincide with internal locations of seals for the blades, or with “hot spots” that have been identified, for example. A stiffener ring may be shrunk with an interference fit into each notch through inducing temperature differentials between the ring and the case. The radially compressive circumferential force exerted by each ring can inhibit the low or high pressure turbine case from expanding as much as it would otherwise. In some applications, a stiffener ring can improve blade tip clearance or counterbalance “hot spots”, stiffen the case, improve case cooling, or other benefits, depending upon the particular application. In one embodiment, notches may be avoided. In an alternate embodiment, C-rings, or multiple segmented rings, may be coupled together by hydraulic, electrical, or other means and actuated by a controller to exert adjustable radially compressive circumferential force. Other embodiments are described and claimed.

1 . A method, comprising: 
 encircling an outer circumferential surface of a turbine case of a gas turbine jet engine using an inner circumferential surface of a stiffener ring; and    applying radially compressive forces to said outer circumferential surface of said turbine case, along the length of the circumference of said inner circumferential surface, using said stiffener ring encircling said turbine case.    
     
     
         2 . The method of  claim 1  wherein said radially compressive force applying includes shrink interference fitting said stiffener ring inner circumferential surface to said outer circumferential surface of said turbine case.  
     
     
         3 . The method of  claim 1  wherein said radially compressive force applying includes seating said stiffener ring inner circumferential surface within a notch defined by said outer circumferential surface of said turbine case and shaped to secure said stiffener ring against displacement in a direction longitudinal to said turbine case.  
     
     
         4 . The method of  claim 1  wherein said turbine case surrounds a turbine adapted for rotation within said turbine case along an axis of rotation wherein said radially compressive forces are directed to a center located on said axis of rotation.  
     
     
         5 . The method of  claim 4  wherein said turbine case has a seal encircling tips of said turbine blades of said turbine and wherein said radially compressive force applying confines the clearance between said seal and said blade tips to be within a predetermined range.  
     
     
         6 . The method of  claim 5  wherein said turbine case is formed of a first material and wherein said stiffener ring is formed of a second material that is different from said first material of said turbine case, said second material having a lower coefficient of thermal expansion than said first material of said turbine.  
     
     
         7 . The method of  claim 5  wherein said radially compressive forces applied to said outer circumferential surface of said turbine case, form an indentation in said outer circumferential surface along the length of the circumference of said inner circumferential surface of the stiffener ring, as the temperature of the turbine case rises.  
     
     
         8 . The method of  claim 1  further comprising redesigning the engine to reduce blade tip clearance as compared to the blade tip clearance of said engine absent said radially compressive force applying.  
     
     
         9 . The method of  claim 1  wherein said applying radially compressive forces permits at least one of the following to be reduced during operation of said engine: a) turbine case out-of-roundness; b) specific fuel consumption; c) clearance between an inner surface of said turbine case and blade tips of said turbine; d) exhaust gas temperature; e) exhaust gas pollution.  
     
     
         10 . The method of  claim 1  further comprising: 
 encircling a second outer circumferential surface of said turbine case of said gas turbine jet engine using a second inner circumferential surface of a second stiffener ring; and    applying radially compressive forces to said second outer circumferential surface of said turbine case, along the length of the circumference of said second inner circumferential surface, using said second stiffener ring encircling said turbine case.    
     
     
         11 . A method of operating a gas turbine jet engine, comprising: 
 rotating a turbine within a turbine case along an axis of rotation; and    applying radially compressive forces to an outer circumferential surface of said turbine case using a stiffener ring encircling said turbine case, said radially compressive forces being applied along the length of the circumference of an inner circumferential surface of said stiffener ring and directed to a center positioned on said axis of rotation.    
     
     
         12 . The method of  claim 11  wherein said turbine case has a seal encircling tips of said turbine blades of said turbine and wherein said radially compressive force applying confines the clearance between said seal and said blade tips to be within a predetermined range as said turbine rotates within said turbine case.  
     
     
         13 . The method of  claim 11  further comprising dissipating heat from said turbine case using said stiffener ring.  
     
     
         14 . The method of  claim 11  further comprising redesigning the engine to reduce blade tip clearance as compared to the blade tip clearance of said engine absent said radially compressive force applying.  
     
     
         15 . The method of  claim 11  wherein said applying radially compressive forces permits at least one of the following to be reduced during operation of said engine: a) turbine case out-of-roundness; b) specific fuel consumption; c) clearance between an inner surface of said turbine case and blade tips of said turbine; d) exhaust gas temperature; e) exhaust gas pollution.  
     
     
         16 . The method of  claim 15  wherein said turbine case is formed of a first material and wherein said stiffener ring is formed of a second material that is different from said first material of said turbine case, said second material having a lower coefficient of thermal expansion than said first material of said turbine.  
     
     
         17 . The method of  claim 11  further comprising applying radially compressive forces to a second outer circumferential surface of said turbine case using a second stiffener ring encircling said turbine case, said radially compressive forces being applied along the length of the circumference of a second inner circumferential surface of said second stiffener ring and directed to a center positioned on said axis of rotation.  
     
     
         18 . A gas turbine jet engine, comprising: 
 a turbine case having an outer circumferential surface;    a turbine adapted to rotate along an axis of rotation within said turbine case; and    a stiffener ring having an inner circumferential surface adapted to apply radially compressive forces to said outer circumferential surface of said turbine case, along the length of the circumference of said inner circumferential surface.    
     
     
         19 . The engine of  claim 18  wherein said stiffener ring is affixed to said turbine case with a shrink interference fitting which causes said stiffener ring to apply said radially compressive forces to said outer circumferential surface of said turbine case.  
     
     
         20 . The engine of  claim 18  wherein said outer circumferential surface of said turbine case defines a notch adapted to receive said stiffener ring and secure said stiffener ring against displacement in a direction longitudinal to said turbine case.  
     
     
         21 . The engine of  claim 18  wherein said radially compressive forces are directed to a center located on said axis of rotation.  
     
     
         22 . The engine of  claim 21  wherein said turbine has turbine blade, each of which has a tip at a distal end of each blade, and wherein said turbine case has an inner circumferential surface which has a seal encircling said tips of said turbine blades of said turbine and wherein said radially compressive force applied by said stiffener ring confines the clearance between said seal and said blade tips to be within a predetermined range.  
     
     
         23 . The engine of  claim 21  wherein said outer circumferential surface of said turbine case defines a notch adapted to receive said stiffener ring and secure said stiffener ring against displacement in a direction longitudinal to said turbine cases and wherein said notch is at a longitudinal location coinciding with said seal on said inner surface of said turbine case.  
     
     
         24 . The engine of  claim 18  wherein said turbine case is formed of a first material and wherein said stiffener ring is formed of a second material that is different from said first material of said turbine case, said second material having a lower coefficient of expansion than said first material of said turbine case.  
     
     
         25 . The engine of  claim 22  further wherein said stiffener ring permits redesigning the engine to reduce blade tip clearance as compared to the blade tip clearance of said engine absent said radially compressive force applying.  
     
     
         26 . The engine of  claim 22  wherein said stiffener ring permits at least one of the following to be reduced during operation of said engine: a) turbine case out-of-roundness; b) specific fuel consumption; c) clearance between an inner surface of said turbine case and blade tips of said turbine; d) exhaust gas temperature; e) exhaust gas pollution.  
     
     
         27 . The engine of  claim 18  wherein said turbine case has second outer circumferential surface, and wherein said engine further comprises a second stiffener ring having a second inner circumferential surface adapted to apply radially compressive forces to a second outer circumferential surface of said turbine case, along the length of the circumference of said second inner circumferential surface.  
     
     
         28 . A method, comprising: 
 (a) machining at least one notch circumferentially at a predetermined location into an outer surface of a turbine case of a gas turbine jet engine; and    (b) seating a stiffener ring in each said at least one notch through a shrink interference fit;    wherein said stiffener ring applies compressive circumferential force to said turbine case.    
     
     
         29 . The method according to  claim 28  wherein said seating further comprises: 
 heating said stiffener ring to cause a first inside diameter of said stiffener ring to increase to a second inside diameter that is larger than an outside diameter of said at least one notch at an ambient temperature;    positioning said stiffener ring in said at least one notch; and    allowing said stiffener ring to cool to said ambient temperature, causing said stiffener ring to decrease from said second inside diameter toward said first inside diameter, but resisted by said outside diameter of said at least one notch, giving rise to said shrink interference fit.    
     
     
         30 . The method according to  claim 28  wherein said seating further comprises: 
 cooling said turbine case to cause a first outside diameter of said at least one notch to decrease to a second outside diameter that is smaller than an inside diameter of said stiffener ring at an ambient temperature;    positioning said stiffener ring in said at least one notch; and    allowing said turbine case to heat up to said ambient temperature, causing said at least one notch to increase from said second outside diameter toward said first outside diameter, but resisted by said inside diameter of said stiffener ring, giving rise to said shrink interference fit.    
     
     
         31 . The method according to  claim 28  wherein said seating further comprises: 
 heating said stiffener ring to cause a first inside diameter of said stiffener ring to increase to a second inside diameter;    cooling said turbine case to cause a first outside diameter of said at least one notch to decrease to a second outside diameter that is smaller than said second diameter of said stiffener ring;    positioning said stiffener ring in said at least one notch;    allowing said stiffener ring to cool to said ambient temperature; and    allowing said turbine case to heat up to said ambient temperature;    wherein said stiffener ring decreases from said second inside diameter toward said first inside diameter, and said at least one notch increases from said second outside diameter toward said first outside diameter, giving rise to said shrink interference fit.    
     
     
         32 . The method according to  claim 28  wherein said machining further comprises: 
 machining said at least one notch circumferentially into an outer surface of said turbine case at a location coinciding with a labyrinth seal on an inner surface of said turbine case.    
     
     
         33 . The method according to  claim 28  wherein said machining further comprises: 
 machining said at least one notch circumferentially into an outer surface of said turbine case at a location coinciding with a hot spot of said turbine case.    
     
     
         34 . The method according to  claim 28  further comprising: 
 machining said stiffener ring to a predetermined shape to match with a shape of said at least one notch.    
     
     
         35 . The method according to  claim 34  wherein said notch machining comprises machining said at least one notch circumferentially at said predetermined location into said outer surface of said turbine case with a reverse taper; and wherein said stiffener ring machining comprises machining said stiffener ring on an inside diameter to match said reverse taper of said at least one notch.  
     
     
         36 . The method according to  claim 34  wherein said notch machining comprises machining said at least one notch circumferentially at said predetermined location into said outer surface of said turbine case with a chevron shape; and 
 wherein said stiffener ring machining comprises machining said stiffener ring on an inside diameter to match said chevron shape of said at least one notch.    
     
     
         37 . The method according to  claim 34  wherein said stiffener ring machining comprises machining a top surface of said stiffener ring so that when said stiffener ring is seated in said at least one notch, said top surface of said stiffener ring is flush with said outer surface of said turbine case.  
     
     
         38 . The method according to  claim 34  wherein said stiffener ring machining comprises machining said stiffener ring from a nickel-base super alloy.  
     
     
         39 . The method according to  claim 34  wherein said stiffener ring machining comprises machining said stiffener ring from a material that is different from a material of said turbine case, said material of said stiffener ring having a lower coefficient of expansion than said material of said turbine case.  
     
     
         40 . A method according to  claim 34  wherein said notch machining comprises machining said at least one notch into said outer surface of said turbine case in a first direction, wherein a plurality of grooves are formed and aligned on said outer surface in said first direction; and 
 wherein said stiffener ring machining comprises machining an inner surface of said stiffener ring in a second direction, wherein a plurality of grooves are formed and aligned on said inner surface in said second direction;    wherein when said outer surface of said at least one notch and said inner surface of said stiffener ring are seated together, said plurality of grooves on said outer surface of said at least one notch and said plurality of grooves on said inner surface of said stiffener ring align in a cross-hatch manner to each other, increasing the frictional forces between said at least one notch and said stiffener ring and reducing the potential for spinning of said stiffener ring within said at least one notch.    
     
     
         41 . An apparatus for use in a gas turbine jet engine, the apparatus comprising: 
 a turbine case having an outer surface which defines at least one notch machined circumferentially into said outer surface of said turbine case of said gas turbine jet engine at a predetermined location; and    a stiffener ring seated in each said at least one notch through a shrink interference fit;    wherein said stiffener ring applies compressive circumferential force to said turbine case.    
     
     
         42 . The apparatus according to  claim 41  further comprising: 
 a means for heating said stiffener ring to cause a first inside diameter of said stiffener ring to increase to a second inside diameter that is larger than an outside diameter of said at least one notch at an ambient temperature, wherein after said stiffener ring is positioned in said at least one notch, said stiffener ring is allowed to cool to said ambient temperature, causing said stiffener ring to decrease from said second inside diameter toward said first inside diameter, but resisted by said outside diameter of said at least one notch, giving rise to said shrink interference fit.    
     
     
         43 . The apparatus according to  claim 41  further comprising: 
 a means for cooling said turbine case to cause a first outside diameter of said at least one notch to decrease to a second outside diameter that is smaller than an inside diameter of said stiffener ring at an ambient temperature, wherein after said stiffener ring is positioned in said at least one notch, said turbine case is allowed to heat up to said ambient temperature, causing said at least one notch to increase from said second outside diameter toward said first outside diameter, but resisted by said inside diameter of said stiffener ring, giving rise to said shrink interference fit.    
     
     
         44 . The apparatus according to  claim 41  further comprising: 
 a means for heating said stiffener ring to cause a first inside diameter of said stiffener ring to increase to a second inside diameter; and    a means for cooling said turbine case to cause a first outside diameter of said at least one notch to decrease to a second outside diameter that is smaller than said second diameter of said stiffener ring, wherein after said stiffener ring is positioned in said at least one notch, said stiffener ring is allowed to cool to said ambient temperature and said turbine case is allowed to heat up to said ambient temperature, causing said stiffener ring to decrease from said second inside diameter toward said first inside diameter, and said at least one notch to increase from said second outside diameter toward said first outside diameter, giving rise to said shrink interference fit.    
     
     
         45 . The apparatus according to  claim 41  wherein said predetermined location for machining said at least one notch circumferentially into said outer surface of said turbine case is at a location coinciding with a labyrinth seal on an inner surface of said turbine case.  
     
     
         46 . The apparatus according to  claim 41  wherein said predetermined location for machining said at least one notch circumferentially into said outer surface of said turbine case is at a location coinciding with a hot spot of said turbine case.  
     
     
         47 . The apparatus according to  claim 41  wherein said stiffener ring further comprises a predetermined shape machined to match with a shape of said at least one notch.  
     
     
         48 . The apparatus according to  claim 41  wherein said notch has a reverse taper machined into said at least one notch; and wherein said stiffener ring has a matching reverse taper machined on an inside diameter of said stiffener ring.  
     
     
         49 . The apparatus according to  claim 41  further comprising: 
 a chevron shape machined into said at least one notch; and    a matching chevron shape machined on an inside diameter of said stiffener ring.    
     
     
         50 . The apparatus according to  claim 41  wherein said stiffener ring further comprises: 
 a top surface of said stiffener ring machined so that when said stiffener ring is seated in said at least one notch, said top surface of said stiffener ring is flush with said outer surface of said turbine case.    
     
     
         51 . The apparatus according to  claim 41  wherein said stiffener ring is machined from a nickel-base super alloy.  
     
     
         52 . The apparatus according to  claim 41  wherein said stiffener ring is machined from a material that is different from a material of said turbine case, said material having a lower coefficient of thermal expansion than said material of said turbine case.  
     
     
         53 . The apparatus according to  claim 41  further wherein said at least one notch of said turbine case has a machined outer surface which defines a plurality of grooves aligned in a first direction on said machined outer surface of said at least one notch; and 
 wherein said stiffener ring has a machined inner surface which defines a plurality of grooves aligned in a second direction on said machined inner surface of said stiffener ring;    wherein when said outer surface of said at least one notch and said inner surface of said stiffener ring are interference shrink fit together, said plurality of grooves on said outer surface of said at least one notch and said plurality of grooves on said inner surface of said stiffener ring align in a cross-hatch manner to each other, increasing the frictional forces between said at least one notch and said stiffener ring and reducing the potential for spinning of said stiffener ring within said at least one notch.    
     
     
         54 . A method comprising: 
 (a) machining at least one notch circumferentially at a predetermined location into an outer surface of a turbine case of a gas turbine jet engine;    (b) seating a stiffener ring in each said at least one notch, said stiffener ring having a first end and a second end;    (c) linking said first end and said second end of said stiffener ring to an actuator; and    (d) actuating said actuator to pull said first and second ends of said stiffener ring together;    wherein said stiffener ring applies compressive circumferential force to said turbine case.    
     
     
         55 . The method according to  claim 54  wherein said machining further comprises machining said at least one notch circumferentially into an outer surface of said turbine case at a location coinciding with a labyrinth seal on an inner surface of said turbine case.  
     
     
         56 . The method according to  claim 54  wherein said machining further comprises machining said at least one notch circumferentially into an outer surface of said turbine case at a location coinciding with a hot spot of said turbine case.  
     
     
         57 . The method according to  claim 54  further comprising machining said stiffener ring to a predetermined shape to match with a shape of said at least one notch.  
     
     
         58 . The method according to  claim 54  further comprising machining said stiffener ring from a nickel-base super alloy.  
     
     
         59 . The method according to  claim 54  further comprising machining said stiffener ring from a material that is different from a material of said turbine case, said material of said stiffener ring having a lower coefficient of thermal expansion than said material of said turbine case.  
     
     
         60 . The method according to  claim 54  further comprising: 
 connecting a controller to said actuator through an electrical connection;    receiving in said controller a plurality of temperature readings from a plurality of temperature sensors located near said stiffener ring; and    processing by said controller said plurality of temperature readings to determine how much to pull said first and second ends of said stiffener ring together by said actuator to exert a predetermined compressive circumferential force on said turbine case.    
     
     
         61 . The method according to  claim 54  wherein said stiffener ring is a one of a c-ring, a chain like multiple segmented ring, and a strip of non-metallic material.  
     
     
         62 . An apparatus for use in a gas turbine jet engine, the apparatus comprising: 
 a turbine case having an outer surface which defines at least one notch machined circumferentially into said outer surface of said turbine case of the gas turbine jet engine at a predetermined location;    a stiffener ring seated in each said at least one notch, said stiffener ring having a first end and a second end; and    an actuator, wherein said first and second ends are linked to said actuator and said actuator when actuated is adapted to pull said first and second ends together;    wherein said stiffener ring applies compressive circumferential force to said turbine case.    
     
     
         63 . The apparatus according to  claim 62  wherein said turbine case has an inner surface and a labyrinth seal on said inner surface and wherein said predetermined location for machining said at least one notch circumferentially into said outer surface of said turbine case is at a location coinciding with said labyrinth seal on said inner surface of said turbine case.  
     
     
         64 . The apparatus according to  claim 62  wherein said turbine case has a hot spot and wherein said predetermined location for machining said at least one notch circumferentially into said outer surface of said turbine case is at a location coinciding with said hot spot of said turbine case.  
     
     
         65 . The apparatus according to  claim 62  wherein said stiffener ring further comprises a predetermined shape to match with a shape of said at least one notch.  
     
     
         66 . The apparatus according to  claim 62  wherein said stiffener ring is machined from a nickel-base super alloy.  
     
     
         67 . The apparatus according to  claim 62  wherein said stiffener ring is machined from a material that is different from a material of said turbine case, said material of said stiffener ring having a lower coefficient of thermal expansion than said material of said turbine case.  
     
     
         68 . The apparatus according to  claim 62  further comprising: 
 a controller connected to said actuator through an electrical connection; and    a plurality of temperature sensors located near said stiffener ring, wherein said controller is adapted to receive a plurality of temperature readings from said plurality of temperature sensors;    wherein said controller is adapted to process said plurality of temperature readings to determine how much to pull said first and second ends of said stiffener ring together by said actuator to exert a predetermined compressive circumferential force on said turbine case.    
     
     
         69 . The apparatus according to  claim 62  wherein said stiffener ring is a one of a c-ring, a chain like multiple segmented ring, and a strip of non-metallic material.