Abstract:
A seal assembly for use in an engine, such as a scramjet engine, having a movable element, such as inlet cowl flap, is provided. The movable element has an outboard structural member which requires thermal protection. The seal assembly includes a sealing element and a support block for thermally isolating the outboard structural member and for supporting the sealing element. In a preferred embodiment, the sealing element comprises a rope seal having a tadpole construction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The present invention relates to a high temperature dynamic seal for scramjet engines at the interface between fixed and movable engine hardware.  
         [0003]     (2) Prior Art  
         [0004]     As supersonic combustion ram jet (scramjet) technology continues to develop, an important goal will be to improve the propulsion system&#39;s operability and performance. One method of achieving this goal is to incorporate variable geometry into the engine flowpath design. Variable geometry allows for real time optimization of the engine flowpath lines for varying flight conditions. Incorporating a movable cowl inlet flap is one method of achieving variable geometry in a scramjet engine.  
         [0005]     There are many challenges associated with incorporating variable geometry in a scramjet environment. Sealing at the interface between the fixed and movable hardware is one of these challenges. The combination of extreme thermal environment and the pressure differential across this joint makes the seal design solution difficult to identify. The sealing solution must limit overboard leakage of the working fluid (in this case, compressed air) from the engine flowpath so as not to degrade engine performance or cause thermal distress in neighboring hardware. It must accomplish this task in an extremely hostile thermal environment while accommodating the travel of the flap. Local thermal and mechanical distortion in the surrounding hardware must also be accounted for.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, it is an object of the present invention to provide an improved seal design for use in a scramjet engine.  
         [0007]     It is a further object of the present invention to provide a seal design which can be used where high temperature tolerant sealing is required.  
         [0008]     The foregoing objects are attained by the seal design of the present invention.  
         [0009]     In accordance with the present invention, a seal assembly for use in an engine with a movable element and an outboard structural member is provided. The seal assembly broadly comprises a sealing element and means for thermally isolating the outboard structural member and for supporting the sealing element. In a preferred embodiment of the present invention, the sealing element comprises a rope seal having a tail retention feature.  
         [0010]     Also, in accordance with the present invention, an engine broadly comprises a movable element, which movable element has a pair of sides and a cavity in each of the sides. The engine further has a seal assembly adjacent each of the sides. Each seal assembly comprises a support block which fits into the cavity and a sealing member supported by the support block. In a preferred embodiment, the engine comprises a scramjet engine and the movable element is a movable cowl inlet flap.  
         [0011]     Other details of the high temperature dynamic seal for scramjet variable geometry, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of a scramjet engine having a movable cowl inlet flap;  
         [0013]      FIG. 2  is an exploded view of an cowl inlet flap and a seal assembly in accordance with the present invention;  
         [0014]      FIG. 3  is a sectional view of the seal assembly of the present invention;  
         [0015]      FIG. 4  is a cross sectional view of a rope seal element used in the seal assembly of the present invention; and  
         [0016]      FIG. 5  is a sectional view of a cowl flap having the seal assembly of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring now to the drawings,  FIG. 1  illustrates a scramjet engine  10  having a movable cowl inlet flap  12 . The seal assembly of the present invention is intended to prevent gas leakage at the interface  14  between the movable cowl inlet flap  12  and the fixed engine hardware.  
         [0018]     Referring now to  FIG. 2 , the movable cowl inlet flap  12  is provided with a sealing assembly  16  on each of the sides  18  and  20 . Each sealing assembly  16  includes a seal support block  22  and a rope seal  24 . The rope seal  24  preferably has a tadpole construction (as shown in  FIG. 4 ) and may be formed from a high temperature tolerant material such as NEXTEL cloth. The flap&#39;s outboard structural member, or stinger,  26  is constructed with a side cavity  28 . The side cavity  28  houses the seal support block  22 . Two small threaded fasteners (not shown) may be used to retain the block  22  during flap installation and handling. The rope seal  24  runs along the side perimeter of the flap  12  and is held in place using the tail feature  30  on the rope seal  24  (see  FIG. 5 ).  
         [0019]     The support block  22  may be constructed of a high temperature capable insulating material such as a ceramic matrix composite material or a monolithic ceramic material. The ceramic matrix composite material may be a composite material having NEXTEL fibers in an aluminosilicate matrix. The monolithic ceramic material may be zirconia. The monolithic ceramic material may be fully dense or partially dense. The support block  22  provides two primary functions. First, it assists in retaining and supporting the rope seal  24 . Second, it acts as a thermal insulator to the flap&#39;s outboard stringer  26 . This important function prevents compromising the structural integrity of the flap&#39;s primary support structure due to thermal distress.  
         [0020]     The rope seal  24  is preferably constructed in a hoop and installs along the border of the support block  22 , wrapping around the nose  33  of the support block  22  and around the torque arm  34  of the flap  12 . When the flap  12  is installed on the engine, the rope seal  24  is compressed between the flap&#39;s internal and external heat exchange panels  36  and  38 , respectively, and the engine sidewall  40  to approximately 80% of its nominal diameter. The rope seal  24  is responsible for retarding leakage outboard or inboard from the engine flowpath.  
         [0021]     Referring now to  FIG. 3 , the seal assembly  16  is shown installed onto the flap  12 . Also, the flap  12  is shown installed next to the engine sidewall  40 . The seal support block  22  can be seen inserted into the cavity  28  of the outboard stringer  26 . The rope seal  24  is sandwiched between the internal heat exchange panel  36  and the external heat exchange panel  38  and the engine sidewall  40 . It can be seen from this figure that any leakage past the rope seal  24  is contained between the actively cooled engine sidewall  40  and the seal support block  22 . This assembly thus effectively isolates the outboard stinger  26  from any hot gases leaking past the rope seal  24 .  
         [0022]     As shown in  FIG. 3 , the support block  22  extends out past the edge of the heat exchanger panels  36  and  38 , thus supporting the rope seal  24  by forming a shelf  50  for the rope seal  24  to rest on. This extension also helps to minimize the gap between the outboard edge of the flap heat exchange panels  36  and  38  and the engine sidewall  40 , thus reducing the size of the leak path. The support block  22  is preferably designed to be sacrificial should it ever come into contact with the engine sidewall  40  during engine operation.  
         [0023]     The hoop construction of the rope seal  24  serves two purposes. First, it allows for a more effective double seal configuration. Second, this construction helps retain the rope seal  24  during operation.  
         [0024]     As can be seen from  FIG. 4 , the rope seal  24  gets its “tadpole” name from its cross-sectional shape. The rope seal  24  preferably consists of a semi-dense fiber core  52  with a cloth-like overbraid  54  weaved with an additional length forming a tail like structure  30 . The tail  30  is used as a retaining feature. Specifically, when constrained, the tail  30  resists the frictional loads wanting to pull the rope seal  24  out of position when the flap  12  is actuated.  
         [0025]     The core  52  of the rope seal  24  is preferably formed from a NEXTEL material due its high temperature tolerance. The overbraid  54  and the tail  30  may be formed from a NEXTEL cloth or a metallic wire cloth material such as a HAYNES 188 wire cloth. Since the overbraid  54  resists the wiping action of the flap  12  against the engine&#39;s metallic sidewalls, the material forming the overbraid  54  must exhibit good wear characteristics.  
         [0026]     Referring now to  FIG. 5 , this figure shows the support block  22  forming the seal support and the rope seal  24  pulled out to the side. This figure demonstrates how the rope seal  24  fits around the support block  22  and how once installed onto the flap  12 , the tail  30  is then trapped between the support block  22  and the heat exchanger panels  36  and  38 .  
         [0027]     As can be seen from the foregoing description, the seal support block  22  acts to (1) support and retain the rope seal  24 , (2) thermally protect the non-cooled structure members, (3) reduce the effective leakage gap, and (4) acts as a sacrificial item in the event of incidental contact with the flowpath structure of the engine.  
         [0028]     While the seal assembly of the present invention has been described in the context of it being used in a scramjet engine, it could also be used in other types of engines which require high temperature tolerant sealing.  
         [0029]     It is apparent that there has been provided in accordance with the present invention a high temperature dynamic seal for scramjet variable geometry which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.