Abstract:
An exemplary flow control device assembly for a turbomachine includes a flow control device configured to move between a first position and a second position. The flow control device in the first position forces more flow through a plurality of cooling holes than the flow control device in the second position. The plurality of cooling holes are upstream the flow control device relative a direction of flow through the turbomachine.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to a flow control device and, more particularly, to a turbomachine flow control device having a reduced signature. 
         [0002]    Some turbomachines include modulated exhaust flow control devices, especially turbomachines incorporating augmentors. The modulated exhaust flow control devices move between positions that force more air through exhaust cooling passages and positions that force less air through the exhaust cooling passages. Forcing more air through the exhaust cooling passages complicates the path the air must travel before being exhausted from the turbomachine. Reducing the air moving through the exhaust cooling passages can increase thrust, fuel efficiency, or both. More air is typically forced through the exhaust cooling passages when the turbomachine is operating in an augmented mode. 
         [0003]    Tied liners are an example of exhaust cooling passages. The modulated exhaust flow control devices are a type of flow control device. Radar detection devices may detect these modulated exhaust flow control devices. 
       SUMMARY 
       [0004]    A flow control device assembly for a turbomachine according to an exemplary embodiment of the present disclosure includes, among other things, a flow control device configured to move between a first position and a second position. The flow control device in the first position forces more flow through a plurality of cooling holes than the flow control device in the second position. The plurality of cooling holes are upstream the flow control device relative to a direction of flow through the turbomachine. 
         [0005]    In a further non-limiting embodiment of the foregoing flow control device assembly, the flow control device in the first position may block more flow through an exit of a bypass flow path than the flow control device in the second position. 
         [0006]    In a further non-limiting embodiment of either of foregoing flow control device assemblies, the flow control device may be positioned axially closer to an aft end of an exhaust duct than a forward end of the exhaust duct. 
         [0007]    In a further non-limiting embodiment of any of foregoing flow control device assemblies, the flow control device may be positioned radially between the exhaust duct and an outer case of the turbomachine when moving between the first and second positions. 
         [0008]    In a further non-limiting embodiment of any of foregoing flow control device assemblies, the plurality of cooling holes may be in a exhaust duct, and the plurality of cooling holes may all be upstream the flow control device relative to a direction of flow through the turbomachine. 
         [0009]    In a further non-limiting embodiment of any of foregoing flow control device assemblies, the flow control device may be axially spaced from a turbine exhaust case of the turbomachine. 
         [0010]    In a further non-limiting embodiment of any of foregoing flow control device assemblies, the flow control device may be axially spaced from an axially rearmost vane of an exhaust section of the turbomachine. 
         [0011]    In a further non-limiting embodiment of any of foregoing flow control device assemblies, the flow control device may be moveable to positions between the first position and the second position. 
         [0012]    A turbomachine assembly according to another exemplary embodiment of the present disclosure includes, among other things, an exhaust duct extending axially from an exhaust section of a turbomachine. The exhaust duct has a plurality of cooling holes. A flow control device is at an aft end of the exhaust duct. The flow control device is configured to move between a first position and a second position. The flow control device in the first position causes more air to move through the cooling holes than the flow control device in the second position. 
         [0013]    In a further non-limiting embodiment of the foregoing turbomachine assembly, the flow control device may be spaced from an axially rearmost vane of an exhaust section of the turbomachine. 
         [0014]    In a further non-limiting embodiment of either of the foregoing turbomachine assemblies, the flow control device is positioned radially between the exhaust duct and an outer case of the turbomachine. 
         [0015]    In a further non-limiting embodiment of any of the foregoing turbomachine assemblies, the plurality of cooling holes are all upstream the flow control device relative to a direction of flow through the turbomachine. 
         [0016]    In a further non-limiting embodiment of any of the foregoing turbomachine assemblies, the flow control device is axially spaced from a turbine exhaust case of the turbomachine. 
         [0017]    A method of selectively directing flow through cooling holes of a tied exhaust duct according to another aspect of the present disclosure includes moving a flow control device from a first position to a second position to direct more flow through cooling holes of an exhaust duct. The cooling holes are upstream the flow control device. 
         [0018]    In a further non-limiting embodiment of the foregoing method of selectively directing flow through cooling holes, the method may move the flow control device from the first position to the second position to block flow. 
         [0019]    In a further non-limiting embodiment of either of the foregoing methods of selectively directing flow through cooling holes, the flow control device may be located within an aftmost portion of a bypass flowpath of a turbomachine having the exhaust duct. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0020]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0021]      FIG. 1  shows a section view of an example turbomachine. 
           [0022]      FIG. 2  shows an aft end view of the turbomachine of  FIG. 1 . 
           [0023]      FIG. 3  shows a close up view of a portion of the turbomachine of  FIG. 2 . 
           [0024]      FIG. 4A  shows a schematic section view of an example flow control device in a first position. 
           [0025]      FIG. 4B  shows a schematic section view of an example flow control device in a second position. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring to  FIGS. 1 to 3 , a gas turbine engine  10  is an example type of turbomachine. The engine  10  includes a fan section  12 , a compressor section  14 , a combustor section  16 , a turbine section  18 , a turbine exhaust case  20 , and an exhaust nozzle section  22 . The compressor section  14 , combustor section  16 , and turbine section  18  are generally referred to as the core engine. The turbine exhaust case  20  forms a portion of an augmentor for the engine  10 . An axis A extends longitudinally through the engine  10 . 
         [0027]    Although depicted as a two-spool gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with such two-spool designs. That is, the teachings may be applied to other types of turbomachines and gas turbine engines, including three-spool architectures. 
         [0028]    In some examples, the engine  10  may incorporate a geared architecture  24  that allows a fan of the fan section  12  to rotate at a slower speed than a turbine that is driving the fan. The geared architecture  24  may include an epicyclic geartrain, such as a planetary geartrain, or some other gear system. 
         [0029]    In the example engine  10 , flow moves from the fan section  12  to a bypass flowpath B. Flow from the bypass flowpath B through the exhaust nozzle section  22  generates forward thrust. The compressor section  14  drives flow along a core flowpath. Compressed air from the compressor section  14  communicates through the combustor section  16 . The products of combustion expand through the turbine section  18 . 
         [0030]    The turbine exhaust case  20  of the example engine  10  includes an inner case  26 , an outer case  30 , and an annular array of vanes  34  extending radially therebetween. The vanes  34  are the axially rearmost vanes  34  in the turbine exhaust case  20 . The vanes  34  are film cooled in this example using cooling air that has moved radially through the vanes  34  from the inner case  26 , which comprises a cooled tailcone in this example. 
         [0031]    The vanes  34  each house a fuel spraybar and flameholders. These devices also form portions of the augmentor for the engine  10 . The spraybar supports a plurality of fuel injector assemblies at varied radial positions. When the augmentor is on, fuel sprays into the turbine exhaust case  20  from the fuel injector assemblies. The fuel is ignited to provide additional thrust to the engine  10  as flow from the core engine mixes with the bypass flow B in the exhaust nozzle section  22  and is exhausted from the engine  10 . 
         [0032]    The turbine exhaust case  20  includes an exhaust duct, which, in this example, is a tied liner  38 . In this example, the tied liner  38  extends axially from a position aligned with the vanes  34  to an aft end portion  40 . The tied liner  38  includes a plurality of apertures  42 . Fluid, such as air, from the bypass flow path B is selectively moved through the plurality of apertures  42  to cool the tied liner  38 . 
         [0033]    In this example, portions of the engine  10  downstream from the tied liner  38  are considered the nozzle section  22 , which may include convergent flaps that move to direct flow from the engine. 
         [0034]    In this example, a flow control device  46  is moved between a first position ( FIG. 4A ) and a second position ( FIG. 4B ) to alter the amount of air that is moved through the tied liner  38  before entering the exhaust nozzle section  22 . 
         [0035]    The flow control device  46 , in this example, is positioned radially between the aft end portion  40  of the tied liner  38  and an outer casing  58  of the engine  10 . The flow control device  46 , in this example, is positioned axially at an exit  50  of the bypass flow path B of the engine  10 . Flow that moves through the exit  50  mixes with flow from the core engine within the exhaust nozzle section  22 . 
         [0036]    Although shown positioned at the exit  50 , the example flow control device  46  could be located at other axial positions. For example, the flow control device  46  could be further forward, with some of the plurality of apertures  42  both upstream and downstream from the flow control device  46 . In such axial positions, the flow control device  46  is axially spaced from the vanes  34  and a turbine exhaust case of the engine  10 . 
         [0037]    The flow control device  46  in the first position blocks more flow through the exit  50  than the flow control device  46  in the second position. In one example, the flow control device  46  permits no flow through the exit  50  when the flow control device  46  is in the second position. In other examples, the flow control device  46  permits some flow through the exit  50  when the flow control device  46  is in the second position. 
         [0038]    Permitting more flow through the exit  50  causes less flow to move through the plurality of apertures  42 . Permitting less flow through the exit  50  causes more flow to move through the plurality of apertures  42 , which increases cooling of the tied liner  38 . When the engine  10  is operating in augmented mode, the flow control device  46  is moved to a first position so that more flow is moved through the plurality of apertures  42  and cooling is enhanced. 
         [0039]    A controller  64  is operably coupled to the flow control device  46  in this example. The controller  64  is configured to automatically move the flow control device  46  between open and closed positions depending on cooling requirements of the tied liner  38 , switching to an augmented flight mode, etc. The controller  64  is operated by a pilot in another example. 
         [0040]    Many types of flow control devices could be used to selectively block flow through the exit  50  of the flow path  54 . For example, the flow control device  46  could be an inflatable variable area device. The flow control device  46  could also be an arrangement of mechanical devices, such as a flap, that are pivotable back and forth across the flow path  54 . In another example, the flow control device  46  includes a set of vanes. Some of the vanes are stationary and others circumferentially movable. The vanes are aligned to create openings for flow, or misaligned to block flow. In yet another example, the flow control device  46  is a series of vanes that pivot about their axes to open and close. In yet another example, the flow control device  46  translates axially to open a passage for flow or to close the passage. 
         [0041]    Features of the disclosed examples include a flow control device that is located at a relatively downstream location. This location facilitates reduced signatures as the location is more shielded from a radar emitting device. This location also may facilitate thrust recovery. 
         [0042]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.