Patent Publication Number: US-2018045140-A1

Title: Aircraft gas turbine engine nacelle

Description:
The present disclosure concerns a nacelle for an aircraft gas turbine engine, and in particular, to a nacelle comprising a thrust reverser. 
     Aircraft gas turbine engines typically comprise thrust reversers configured to provide a thrust component having a reverse flow direction compared to normal flow in forward flight, or to at least provide additional drag, in order to reduce the speed of the aircraft. One known arrangement comprises a “cold stream” thrust reverser, in which blocker doors are deployed to prevent normal flow through the bypass duct rearwardly of the fan, while permitting flow through the engine core. Simultaneously, a sleeve around the perimeter of the nacelle moves axially rearwards, revealing vanes, which redirect bypass air forward, thereby providing reverse thrust. The vanes are typically configured in discrete cascade boxes, with each cascade box typically having an individual arrangement of forward turning vanes. 
     However, the vanes have a relatively large radial thickness, which may increase the overall thickness of the nacelle, and so increase aerodynamic drag in normal flight. A minimum radial thickness is required, since turning the airflow over a smaller distance may generate turbulence. Consequently, there is a need to provide an aircraft gas turbine engine nacelle which overcomes or ameliorates the above problems. 
     According to a first aspect of the invention there is provided an aircraft gas turbine engine nacelle comprising a thrust reversal arrangement, the thrust reversal arrangement comprising: 
     at least one thrust reverser cascade box comprising a fixed structure and a plurality of thrust reverser vanes configured to direct bypass air forwardly;
 
at least a subset of the thrust reverser vanes being translatable and/or pivotable relative to the fixed structure between a deployed position, in which the pivotable and/or translatable vanes define a first volume, and a stowed position, in which the pivotable and/or translatable vanes define a second, smaller volume.
 
     By providing cascade boxes having pivotable and/or translatable thrust reverser vanes, the volume of the vanes can be relatively small when stowed, and sufficiently large when deployed to provide effective airflow turning. 
     Where the vanes are pivotable, the vanes may define a first radial extent when in the deployed position, and a second radial extent when in the stowed position, the second radial extent being smaller than the first radial extent. 
     Where the vanes are translatable, the vanes may define a first axial extent when in the deployed position, and a second axial extent when in the stowed position, the second axial extent being smaller than the first axial extent. 
     A further subset of the vanes may comprise fixed vanes which are fixed relative to the cascade box fixed structure. 
     The thrust reverser arrangement may further comprise one or more fixed vanes. The translatable/moveable vanes may be located downstream in fan flow relative to the fixed vanes. It has been found by the inventors that it is particularly aerodynamically beneficial to reduce the nacelle thickness at an axial position corresponding to a downstream portion of the thrust reverser cascades. Furthermore, at this position, the blocker doors provide some flow redirection, and so the forces on the vanes at this position are less than at the upstream vanes. Consequently, these vanes can be more readily made pivotable, since lower forces are incumbent on them in operation relative to the forward vanes. 
     The nacelle may comprise an aft cowl, which may be moveable between a forward stowed position and a rearward deployed position. The aft cowl may comprise radially inner and outer walls defining a hollow portion therebetween. The pivotable thrust reverser vanes may be at least partly located within the hollow portion when the aft cowl is in the stowed position. The radially outer wall may comprise a guide member configured to engage against the pivotable thrust reverser vanes to move them from the deployed to the stowed position when the aft cowl is moved from the deployed to the stowed position. Advantageously, the pivotable and/or translatable vanes can be moved from the deployed to the stowed position using existing actuators, thereby providing a reliable, low cost actuation method. 
     The pivotable vanes may comprise a pivot point located such that the pivotable vanes are pivotable about a radially inner end. The pivot point may be located radially inwardly of an aerodynamic centre of pressure of the pivotable vanes in use. Advantageously, the pivotable vanes are automatically moveable from the stowed position to the deployed position by airflow through the cascade boxes. 
     The cascade box may comprise one or more stops positioned so as to engage against an axially rearward side of a forwardly adjacent vane when the respective vane is in the deployed position. The one or more stops may be positioned to engage against a forward side of a rearwardly adjacent vane when the respective vane is in the stowed position. Advantageously, a single stop per pivotable vane can be employed to ensure that the pivotable vanes assume a desired angle when in the deployed position to ensure efficient thrust reversal, and to provide clearance between the vanes when in the stowed position. 
     Alternatively or in addition, the thrust reversal arrangement may comprise a vane actuator configured to move the pivotable and/or translatable vanes between the stowed and deployed positions. Advantageously, vibration of the pivotable vanes may be prevented. 
     The vane actuator may comprise a follower arm coupled to an aft cowl actuator. 
     Alternatively, the vane actuator may be configured to actuate the pivotable and/or translatable vanes independently of the aft cowl actuator. Consequently, the vane positions can be adjusted independently of the aft cowl position, thereby permitting variation of the thrust reverser vane angle independently of aft cowl deployment. Consequently, reverse thrust vector and so reverse thrust level can be actively and promptly modulated, without adjusting core rotational speed. 
     At least a subset of the pivotable and/or translatable vanes may be located forwardly of a radially outer external surface of the aft cowl and rearwardly of a radial outer surface of a forward cowl when in the stowed position. Consequently, the vanes define the ambient airwashed nacelle external surface, thereby reducing weight and reducing the radial extent of the nacelle outer surface. 
     Where the vanes are translatable, adjacent translatable vanes may be interconnected by a scissors mechanism. 
     Where the thrust reversal arrangement comprises a pivotable vane actuation arrangement, the pivot point may be provided at a radial position corresponding to the aerodynamic centre of pressure. Advantageously, loads on the actuator are reduced. 
     According to a second aspect of the invention there is provided an aircraft comprising a gas turbine engine nacelle in accordance with the first aspect of the invention. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention. 
    
    
     
       Embodiments of the invention will now be described by way of example only, with reference to the figures, in which. 
         FIG. 1  is a sectional side view of a gas turbine engine; 
         FIG. 2  is a schematic sectional side view of a first thrust reverser of a nacelle suitable for the gas turbine engine of  FIG. 1  in a deployed position; 
         FIG. 3  is a schematic sectional side view of the thrust reverser of  FIG. 2  in a stowed position; 
         FIG. 4  is a schematic sectional side view of part of a second thrust reverser of a nacelle suitable for the gas turbine engine of  FIG. 1  in a deployed position; 
         FIG. 5  is a schematic sectional side view of the thrust reverser of  FIG. 4  in a stowed position; 
         FIG. 6  is a schematic sectional side view of part of a third thrust reverser of a nacelle suitable for the gas turbine engine of  FIG. 1  in a deployed position; 
         FIG. 7  is a schematic sectional side view of the thrust reverser of  FIG. 6  in a stowed position; 
         FIG. 8  is a schematic sectional side view of part of a fourth thrust reverser of a nacelle suitable for the gas turbine engine of  FIG. 1  in a deployed position; 
         FIG. 9  is a schematic sectional side view of the thrust reverser of  FIG. 8  in a stowed position; 
         FIG. 10  shows a close-up view of region A of the thrust reverser of  FIG. 8  in the stowed position; and 
         FIG. 11  shows a close-up view of region A of the thrust reverser of  FIG. 8  in the deployed position. 
     
    
    
     With reference to  FIGS. 1 to 3 , a gas turbine engine having a first thrust reversal arrangement is generally indicated at  10 . As shown in  FIG. 1 , the engine  10  has a principal and rotational axis  11 . The engine  10  comprises, in axial flow series, an air intake  12 , a propulsive fan  13 , an intermediate pressure compressor  14 , a high-pressure compressor  15 , combustion equipment  16 , a high-pressure turbine  17 , and intermediate pressure turbine  18 , a low-pressure turbine  19  and a core exhaust nozzle  20 . A bypass nacelle  21  generally surrounds the engine  10  and defines both the intake  12  and the fan exhaust nozzle  22  and also defines a hot core stream outlet  20  at an aft end thereof. The nacelle  21  incorporates a thrust reverser arrangement  23  within an aft part thereof. 
     The gas turbine engine  10  works in the conventional manner so that air entering the intake  12  is accelerated by the fan  13  to produce two air flows: a first air flow A into the intermediate pressure compressor  14  and a second air flow B which passes through a bypass duct  48  to provide propulsive thrust. The intermediate pressure compressor  14  compresses the air flow directed into it before delivering that air to the high pressure compressor  15  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  15  is directed into the combustion equipment  16  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  17 ,  18 ,  19  before being exhausted through the nozzle  20  to provide additional propulsive thrust. The high  17 , intermediate  18  and low  19  pressure turbines drive respectively the high pressure compressor  15 , intermediate pressure compressor  14  and fan  13 , each by suitable interconnecting shaft. 
     In normal forward flight, the engine  10  is configured such that exhaust flows from the fan exhaust nozzle  22  and engine core nozzle  22  are directed in first axial direction X, shown in  FIGS. 1 and 2 . The direction X also defines a rearward direction being generally opposite to a forward flight direction. 
     Referring to  FIG. 2 , a first thrust reverser arrangement  23  is shown, which is configured to block normal flow in the direction X through the fan exhaust nozzle  22 , and provide airflow having an axially forward component Y (i.e. having a component in an opposite direction to the first axial direction X) when actuated. In general, air is also directed in a radial direction when the thrust reverser arrangement  23  is in operation. 
     The arrangement comprises a forward cowl  24 , which is fixed. The forward cowl  24  comprises a radially inner wall  49  and a radially outer wall  50 . Rearwardly of the forward cowl  24  is an aft cowl  25  (also known as a “transcowl”), which is axially moveable relative to the forward cowl  24  between a forward, stowed position (as shown in  FIGS. 1 and 3 ) and a rearward, deployed position (as shown in  FIG. 2 ). 
     When in the stowed position, the forward and aft cowls  24 ,  25  abut one another, such that air flows through the bypass duct  22  and out through the primary fan exhaust nozzle  22 . When deployed, the aft cowl  25  is moved rearwardly, such that an annular gap  52  is opened in the nacelle  21  between the forward and aft cowls  24 ,  25 . Simultaneously, blockers doors  26  are moved into a deployed position (again shown in  FIG. 2 ), such that the nozzle  22  is blocked by the door  26 . Drag links  27  attached to the blocker doors  26  support the blocker doors  26  when in the deployed position. Consequently, airflow is caused to flow out the annular gap  52  between the forward  24  and aft  25  cowls. 
     A thrust reverser cascade box  28  is provided. The thrust reverser cascade box is located in the gap  52  when the aft cowl  25  and blocker doors  26  are deployed. In general, a plurality of thrust reverser cascade boxes  28  are provided, distributed circumferentially around the nacelle  21 . Each thrust reverser cascade box  28  comprises a plurality of vanes. A subset of these vanes comprise fixed thrust reverser vanes  29 , which are configured to direct air exiting through the cascades  28  out of the annular gap  52  in a radially outward and axially forward direction Y. i.e. in a direction having a forward component, opposite to the direction X. Each thrust reverser vane  29  extends in a generally circumferential direction and in a radial direction, and turns from a generally radial direction at a radially inner end toward a generally axially forwardly direction at a radially outer end, such that air exiting through the gap  52  is turned forwardly. 
     The fixed cascade vanes  29  are located at a forward portion of the cascade box  28 , extending from a forward mounting  30  which provides a fixed structure for the cascade box  28 . A further subset of vanes comprises a plurality of pivotable thrust reverser vanes  31 , which are provided downstream in fan flow B of the fixed cascade vanes  29  at a rear portion of the cascade box  28 . The pivotable vanes  31  are pivotable between a deployed position (shown in  FIG. 2 ), and a stowed position (shown in  FIG. 3 ). Again, the vanes  31  extend in a generally circumferential direction and in a radial direction, and turn from a generally radial direction at a radially inner end toward a generally axially forwardly direction at a radially outer end, such that air exiting through the gap  52  is turned forwardly. 
     When in the deployed position, each pivotable vane  31  defines a first radial extent R 1  defined by a radial distance between a radially inner and a radially outer end of a respective vane  31 . When in the stowed position, the pivotable vanes  31  each define a second radial extent R 2  defined by the radial distance between a radially inner and a radially outer end. As can be seen from  FIGS. 2 and 3 , the first radial extent R 1  is greater than the second radial extent R 2 . In view of the smaller second radial extent R 2 , the pivotable vanes  31  occupy a smaller volume when in the stowed position that when in the deployed position. The pivotable vanes  31  are pivotable at a pivot point defined by a hinge  32  located at a radially inner end of each vane  31 . Each hinge  32  allows free pivoting movement of a respective pivotable vane  31 . 
     Each cascade box  28  comprises an axially extending side wall  34 , which extends from the forward end to the rearward end. The side wall  34  extends axially in a radial plane, and defines an outer extent which thins toward an aft end, as shown in  FIG. 2 , such that the pivotable vanes  31  have a greater radial extent than the side wall  34  at the aft end. Consequently, vanes  31  radially project from a radially outer end of the side wall  34 . 
     The aft cowl  25  comprises a guide member in the form of a rail  33  (shown by dotted lines in  FIGS. 2 and 3 , though it will be understood that the rail  33  is generally continuous), which is mounted to an internal side of a radially outer surface of the cowl  25 . 
     In use, when transitioning from the deployed position (shown in  FIG. 2 ) to the stowed position (shown in  FIG. 3 ), the aft cowl  25  translates forwardly, and the blocker doors  26  and drag links  27  return to their stowed positions. As the aft cowl  25  translates forwardly, the rail  33  engages against a radially outer end of a rearward surface of each pivotable vane  31 , at a point radially outwardly of the side wall  34 . As the aft cowl  25  further translates forwardly, the vanes  31  are pivoted such that a radially outer end moves forwardly, thereby pivoting the vanes  31  to the stowed position. The cowl  25  continues to translate forwardly until the cowls  24 ,  25  abut, and the nacelle  21  is thereby in the stowed position. As can be seen, different vanes  31  at different axial positions may pivot to a different extent, thereby defining a different radial extent relative to one another. This is because of the shape of the rail  33 , which generally has a greater radial extent at a forward end relative to a rearward end. 
     When moving from the stowed position to the deployed position, the aft cowl  25  moves rearwardly from the stowed position, in which the cowls  24 ,  25  abut. As the aft cowl  25  moves toward the deployed position, the rail  33  disengages from the vanes  31 , thereby allowing free movement of the vanes  31 . Meanwhile, the blocker door  26  and drag link  27  move to their deployed positions, thereby redirecting bypass airflow B through the annular gap  52 , and through the vanes  31 . Since the hinges  32  are located at a radially inner end of the vanes  31 , the airflow causes the vanes  31  to rotate such that the radially outer ends move rearwardly, and so the vanes are moved to the deployed position. As will be understood, this is a consequence of the hinges  32  being located at a radially inward end of the vanes,  31 , i.e. radially inwardly of a centre of pressure of the respective vane  31 . Consequently, since the vanes  31  are shaped to redirect air forwardly, airflow through the vanes  31  causes them to pivot to the deployed position. It will be understood thereby that this effect will be achieved provided the hinges  32  are located radially inwardly of the centre of pressure of the respective vane  31 , and need not be located at a radially inner extremity. 
     Consequently, the vanes  31  are moved between the deployed and stowed positions without a requirement for further actuation mechanisms, save for the rail  33 . In some instances, the rail could be omitted, the inner surface of the aft cowl acting as an actuator. 
       FIGS. 4 and 5  show a second thrust reverser arrangement  123  for the gas turbine engine  10  in a deployed position and a stowed position respectively. The thrust reverser arrangement  123  is similar to the arrangement  23 , with only differences being described. The thrust reverser arrangement  123  comprises a cascade box  128  comprising forward fixed vanes  129  and rearward pivotable vanes  131 . Each pivotable vane comprises a hinge  132  to provide pivoting movement. 
     The cascade further comprises a plurality of stops  135 , with one stop  135  being provided rearwardly of each pivotable vane  131 . As shown in  FIG. 4 , the stops  135  are positioned such that a rearward surface of a forwardly adjacent vane  131  engages against a respective stop  135  when the arrangement  123  is in the deployed position. Consequently, spacing between adjacent vanes  131  is ensured to enable flow to progress between adjacent vanes  131 . An aft cowl (not shown) having a rail (not shown) is provided, which engages against the vanes  129  to move them between the stowed and deployed positions, as in the first arrangement  23 . 
     As shown in  FIG. 5 , the stops  135  are positioned such that a forward surface of a rearwardly adjacent vane  131  engages against a respective stop  135  when the arrangement  123  is in the stowed position. Consequently, a spacing is ensured when the arrangement  123  is in the stowed position, which may prevent damage to the radially outer ends of the vanes  131  when in the stowed position. 
       FIGS. 6 and 7  show a third thrust reverser arrangement  223  for the gas turbine engine  10  in a deployed position and a stowed position respectively. The thrust reverser arrangement  223  is similar to the arrangement  23 , with only differences being described. The thrust reverser arrangement comprises a cascade box  228  comprising forward fixed vanes  229  and rearward pivotable vanes  231 . Each pivotable vane comprises a hinge  232  to provide pivoting movement. 
     A different actuation arrangement is provided to move the pivotable vanes  229  between the stowed and deployed positions. The aft cowl comprises a follower arm  236  which is fixedly mounted thereto, and therefore moves with the aft cowl  225  when it moves between the deployed and stowed positions. 
     When in the deployed position (shown in  FIG. 6 ), the follower arm  236  engages against a forward side of each vane  229 , to thereby urge the respective vane  229  toward a deployed position. Similarly, when moved toward the stowed position, the follower arm  236  engages against a rearward surface to urge the respective vane  229  to the stowed position. Consequently, the vanes  229  can be moved between the stowed and deployed positions without requiring a further actuator, but without relying on airflow through the cascade box  228  to ensure correct positioning. 
       FIGS. 8 and 9  show a fourth thrust reverser arrangement  423  comprising a cascade box  428 , fixed structure  430  and aft cowl  425  in a deployed and a stowed position respectively. Again, the thrust reverser arrangement is similar to that of the previous arrangements, except that the vanes are hinged in a different way, and are translatable. 
       FIG. 11  shows a close-up of the area A of  FIG. 8 . As can be seen, a plurality of translatable vanes  431  are provided. Each translatable vane  431  is mounted to a scissors mechanism comprising first and second arms  454 ,  456 . The first and second  454 ,  456  arms are linked by a first pivot point  458  at an intermediate point of each arm  454 ,  456 . Each arm  454 ,  456  is also linked to a first and second further second arm at distal ends thereof by second and third pivot points  460 ,  462 . Consequently, movement of any of the arms  454 ,  456  causes axial movement of the remainder of the arms  454 ,  456 , and thereby causes axial movement of the translatable vanes  431 , in a manner similar to a pantograph mechanism. As will be understood, the pivot points  460 ,  462  may be offset axially, such that the vanes  431  pivot as they are translated. 
     The translatable vanes  431  are pivotably mounted to the second pivot points  460 , and are slidable relative to the third pivot points  462 . Consequently, when moved from the deployed to the stowed position, the vanes  431  have a smaller axial extent, and so occupy a smaller volume, as shown in  FIG. 10 . 
     The translatable vanes  431  are actuated by a guide rail  433  mounted to the aft cowl  425 . In operation, the guide rail  433  engages against rearwardmost first and second arms  454 ,  456  when the aft cowl  425  is moved from the deployed position to the stowed position, thereby translating the vanes  431  forwardly. Similarly, where the aft cowl  425  is moved from the stowed to the deployed position, the guide rail  433  disengages from the first and second arms  454 ,  456 . Air from the bypass passage acts against the vanes  431  to translate them rearwardly to the deployed position. Alternatively, the guide rail  433  may be fixed to the first and second arms  431 , such that the vanes  431  are directly actuated by movement of the aft cowl  425 . 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein. 
     For example, the radially outer surface of the aft cowl could be omitted, or may extend such that the aft and forward cowls do not abut when in the stowed position. Consequently, a rearward surface of the pivotable cascade vanes could provide an external air-washed surface of the nacelle. Advantageously, the nacelle depth and weight would be reduced. 
     A separate actuator may be provided, which may actuate each pivotable vane independently of the aft cowl, blocker door and drag link actuator. A separate actuator could be provided for each vane, or a single actuator could be provided for a plurality of pivotable vanes. Consequently, the vanes could be adjusted to control reverse thrust efflux vector, thereby providing additional reverse thrust control.