Method and system for improved blade tip clearance in a gas turbine jet engine

Abstract

A low or high pressure turbine case is machined on its outside surface to form circumferential notches. The notches coincide with the internal locations of labyrinth seals for the blades, or with “hot spots” that have been identified. A stiffener ring is shrunk with an interference fit into each notch through inducing temperature differentials between the ring and the case. The compressive circumferential force exerted by each ring prevents the low or high pressure turbine case from expanding as much as it would otherwise, thus improving blade tip clearance or counterbalancing the “hot spots”, stiffening the case, and improving case cooling. In an alternate embodiment a hydraulic nut may be used to push the ring in place and held by a locking nut. Alternatively, C-rings, or multiple segmented rings, may be coupled together by hydraulic, electrical, or other means and actuated by a controller to exert adjustable compressive circumferential force.

1 . A method for improved blade tip clearance in a gas turbine jet engine, the method comprising the steps of: 
 (a) machining at least one stiffener ring to fit without pressure near a predetermined location on an outer surface of a turbine case of the gas turbine jet engine;    (b) mounting a hydraulic nut on said turbine case adjacent to said at least one stiffener ring;    (c) engaging a piston of said hydraulic nut with said at least one stiffener ring;    (d) pushing said at least one stiffener ring by extending said piston of said hydraulic nut in a direction toward a larger diameter end of said turbine case resulting in an interference fit of said at least one stiffener ring into said predetermined location;    (e) replacing said hydraulic nut with a locking nut, said locking nut having a retainer; and    (f) engaging said retainer of said locking nut with said at least one stiffener ring, wherein said at least one stiffener ring is secured in said predetermined location in said interference fit;    wherein said at least one stiffener ring dissipates heat, applies compressive circumferential force to said turbine case, and prevents said turbine case form going out-of-round during cruise operation of the gas turbine jet engine, improving blade tip clearance.    
     
     
         2 . The method according to  claim 1  wherein pushing step (d) further comprises the step of: 
 extending said piston of said hydraulic nut by an amount calculated to produce a desired said compressive circumferential force on said turbine case by said at least one stiffener ring at said predetermined location.    
     
     
         3 . The method according to  claim 1  wherein machining step (a) further comprises the step of: 
 machining said at least one stiffener ring from a nickel-base super alloy.    
     
     
         4 . The method according to  claim 1  wherein machining step (a) further comprises the step of: 
 machining said at least one stiffener ring from a material that is different from a material of said turbine case, said material having a lower coefficient of expansion than said material of said turbine case.    
     
     
         5 . The method according to  claim 1  wherein machining step (a) further comprises the step of: 
 machining said at least one stiffener ring to fit at an outer surface of said turbine case at a location coinciding with a labyrinth seal on an inner surface of said turbine case.    
     
     
         6 . The method according to  claim 1  wherein machining step (a) further comprises the step of: 
 machining said at least one stiffener ring to fit at an outer surface of said turbine case at a location coinciding with a hot spot of said turbine case.    
     
     
         7 . An apparatus for improving blade tip clearance in a gas turbine jet engine, the apparatus comprising: 
 at least one stiffener ring machined to fit without pressure near a predetermined location on an outer surface of a turbine case of the gas turbine jet engine;    a hydraulic nut mounted on said turbine case adjacent to said at least one stiffener ring;    a piston of said hydraulic nut which engages with said at least one stiffener ring and pushes said at least one stiffener ring by extending from said hydraulic nut in a direction toward a larger diameter end of said turbine case resulting in an interference fit of said at least one stiffener ring into said predetermined location;    a locking nut for replacing said hydraulic nut; and    a retainer of said locking nut which engages with said at least one stiffener ring and secures said at least one stiffener ring in said predetermined location in said interference fit;    wherein said at least one stiffener ring dissipates heat, applies compressive circumferential force to said turbine case, and prevents said turbine case form going out-of-round during cruise operation of the gas turbine jet engine, improving blade tip clearance.    
     
     
         8 . The apparatus according to  claim 7  wherein said piston of said hydraulic nut is extended by an amount calculated to produce a desired said compressive circumferential force on said turbine case by said at least one stiffener ring at said predetermined location.  
     
     
         9 . The apparatus according to  claim 7  wherein said at least one stiffener ring is machined from a nickel-base super alloy.  
     
     
         10 . The apparatus according to  claim 7  wherein said at least one stiffener ring is machined from a material that is different from a material of said turbine case, said material having a lower coefficient of expansion than said material of said turbine case.  
     
     
         11 . The apparatus according to  claim 7  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.  
     
     
         12 . The apparatus according to  claim 7  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.  
     
     
         13 . A method for improved blade tip clearance in a gas turbine jet engine, the method comprising the steps of: 
 (a) machining at least one notch circumferentially at a predetermined location into an outer surface of a turbine case of the gas turbine jet engine;    (b) coating an inside surface of a stiffener ring with a lubricating substance, said stiffener ring having a first end and a second end;    (c) seating said stiffener ring in each said at least one notch;    (d) linking said first end and said second end of said stiffener ring to an actuator; and    (e) actuating said actuator to pull said first and second ends of said stiffener ring together, wherein said coating facilitates slippage of said stiffener ring in said at least one notch when said actuator is actuated;    wherein said stiffener ring dissipates heat, applies compressive circumferential force to said turbine case, and prevents said turbine case form going out-of-round during cruise operation of the gas turbine jet engine, improving blade tip clearance.    
     
     
         14 . A method for improved blade tip clearance in a gas turbine jet engine, the method comprising the steps of: 
 (a) machining at least one notch circumferentially at a predetermined location into an outer surface of a turbine case of the gas turbine jet engine;    (b) coating a surface of said at least one notch with a lubricating substance;    (c) seating a stiffener ring in each said at least one notch, said stiffener ring having a first end and a second end;    (d) linking said first end and said second end of said stiffener ring to an actuator; and    (e) actuating said actuator to pull said first and second ends of said stiffener ring together, wherein said coating facilitates slippage of said stiffener ring in said at least one notch when said actuator is actuated;    wherein said stiffener ring dissipates heat, applies compressive circumferential force to said turbine case, and prevents said turbine case form going out-of-round during cruise operation of the gas turbine jet engine, improving blade tip clearance.    
     
     
         15 . An apparatus for improving blade tip clearance in a gas turbine jet engine, the apparatus comprising: 
 at least one notch machined circumferentially into an outer surface of a 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;    a lubricating substance coated on an inside surface of said stiffener ring; and    an actuator, wherein said first and second ends are linked to said actuator and said actuator when actuated pulls said first and second ends together, said lubricating substance facilitating slippage of said stiffener ring in said notch when said actuator is actuated;    wherein said stiffener ring dissipates heat, applies compressive circumferential force to said turbine case, and prevents said turbine case form going out-of-round during cruise operation of the gas turbine jet engine, improving blade tip clearance.    
     
     
         16 . An apparatus for improving blade tip clearance in a gas turbine jet engine, the apparatus comprising: 
 at least one notch machined circumferentially into an outer surface of a 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;    a lubricating substance coated on a surface of said notch; and    an actuator, wherein said first and second ends are linked to said actuator and said actuator when actuated pulls said first and second ends together, said lubricating substance facilitating slippage of said stiffener ring in said notch when said actuator is actuated;    wherein said stiffener ring dissipates heat, applies compressive circumferential force to said turbine case, and prevents said turbine case form going out-of-round during cruise operation of the gas turbine jet engine, improving blade tip clearance.