Variable area nozzle

Abstract

An exhaust nozzle assembly ( 18 ) for a gas turbine engine ( 10 ), the assembly ( 18 ) comprises a main axis ( 20 ), an inner nozzle ( 19 ), an outer nozzle ( 17 ), a translatable centre-body ( 44 ) and a means for translating the centre-body ( 49 ) between a forward position and a rearward position. The centre-body ( 44 ) is disposed radially inwardly of the inner nozzle ( 19 ) thereby partly defining an inner duct ( 35 ) for a core engine gas flow ( 28 ), an outer duct ( 17 ) for a bypass gas flow ( 30 ) is defined by the inner nozzle ( 19 ) and the outer nozzle ( 17 ). The outer nozzle ( 17 ) extends downstream of the inner nozzle ( 19 ) and with the centre-body ( 44 ) defines a final mixing duct ( 36 ) having a final exhaust exit area ( 38 ). When the centre-body ( 44 ) is in the forward position the final exhaust exit area ( 38 ) is at a maximum area, and when the centre-body ( 44 ) is in a rearward position the final exhaust exit area ( 38 ) is at a minimum area.

1 . An exhaust nozzle assembly for a gas turbine engine, the assembly comprises a main axis, an inner nozzle, an outer nozzle, a translatable centre-body and a means for translating the centre-body between a forward position and a rearward position; the centre-body is disposed radially inwardly of the inner nozzle thereby partly defining an inner duct for a core engine gas flow, an outer duct for a bypass gas flow is defined by the inner nozzle and the outer nozzle, the outer nozzle extends downstream of the inner nozzle and with the centre-body defines a final mixing duct having a final exhaust exit area; wherein when the centre-body is in the forward position the final exhaust exit area is at a maximum area, and when the centre-body is in a rearward position the final exhaust exit area is at a minimum area.  
     
     
         2 . An exhaust nozzle assembly as claimed in  claim 1  wherein the inner nozzle defines a core exhaust exit area, and when the centre-body is in the forward position the core exhaust exit area is at a maximum area, and when the centre-body is in a rearward position the core exhaust exit area is at a minimum area.  
     
     
         3 . An exhaust nozzle assembly as claimed in  claim 1  wherein the inner nozzle defines a core exhaust exit area, and when the centre-body is in the forward position the core exhaust exit area is at a minimum area, and when the centre-body is in a rearward position the core exhaust exit area is at a maximum area.  
     
     
         4 . An exhaust nozzle assembly as claimed in  claim 1  wherein when the centre-body is in the rearward position the centre-body and the outer nozzle define, in axial flow series, a converging portion and a diverging portion, the mixed exhaust flow then exits the final exhaust exit area which is at the minimum area.  
     
     
         5 . An exhaust nozzle assembly as claimed in  claim 1  wherein the centre-body comprises, in a downstream direction, a parallel portion, a waist, a diverging section, a maximum diameter portion and a taper; the parallel portion is substantially parallel and a part of which is slidably engaged with a static core engine structure.  
     
     
         6 . An exhaust nozzle assembly as claimed in  claim 5  wherein when the centre-body is in the forward position the waist is generally axially aligned with the core exhaust exit area thereby providing the maximum core exhaust exit areas; when the centre-body is in the rearward position the parallel portion is axially aligned with core exhaust exit area thereby minimising the exit area.  
     
     
         7 . An exhaust nozzle assembly as claimed in  claim 1  wherein the centre-body comprises, in a downstream direction, a parallel portion, a diverging section, a maximum diameter portion and a taper; the parallel section is substantially parallel and a part of which is slidably engaged with a static core engine structure.  
     
     
         8 . An exhaust nozzle assembly as claimed in  claim 7  wherein when the centre-body is in the forward position or the rearward position the diverging section is generally axially aligned with core exhaust exit area thereby providing a constant core exhaust exit area.  
     
     
         9 . An exhaust nozzle assembly as claimed in  claim 7  wherein when the centre-body is in the forward position the waist is axially aligned with the core exhaust exit area thereby providing the maximum core exhaust exit areas; when the centre-body is in the rearward position the parallel portion is axially aligned with core exhaust exit area and thereby minimising the core exhaust exit area.  
     
     
         10 . An exhaust nozzle assembly as claimed in  claim 5  wherein when the centre-body is in the forward position the downstream end of the taper is generally axially aligned with the final exhaust exit area thereby providing the maximum final exit area; when the centre-body is in the rearward position the maximum diameter portion is generally axially aligned with the final exhaust exit area thereby minimising the final exit area.  
     
     
         11 . An exhaust nozzle assembly as claimed in  claim 5  wherein a means for translating the centre-body between a forward position and a rearward position comprises at least one actuator mounted within and to the static core engine structure, the actuator having a piston which is attached to a mounting on the translating centre-body.  
     
     
         12 . An exhaust nozzle assembly as claimed in  claim 1  wherein when the centre-body is in the rearward position the engine is in high-speed mode and when the centre-body is in the forward position the engine is in low-speed mode.  
     
     
         13 . An exhaust nozzle assembly as claimed in  claim 1  wherein when the engine operates between low-speed mode and high-speed mode the centre-body is positioned between the forward position and the rearward position.  
     
     
         14 . A gas turbine engine comprising an exhaust nozzle assembly as claimed in  claim 1.