Abstract:
An inlet guide vane provides improved, smooth airflow and avoids separation of flow even at high incidence angles. The inlet guide vane includes a strut having opposite side surfaces that are continuously curved to provide a controlled velocity distribution at the trailing edge of the strut. The inlet guide vane further includes a flap having a leading edge aligned behind the trailing edge of the strut. Generally, the strut and the flap are designed together so that low momentum air in the gap between the strut and the flap will be energized and entrained in the boundary layer of the flap. The airflow from the gap will remain attached to the flap to improve the flow from the flap.

Description:
[0001]     This invention was made with government support under contract number N00019-02-C3003 awarded by the United States Navy. The government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to turbine engines and more particularly to a variable geometry inlet guide vane.  
         [0003]     Some gas turbine engines, particularly gas turbine engines for military aircraft, include variable geometry inlet guide vanes positioned in front of the compressor inlet or in front of the fan. The inlet guide vanes each include a fixed strut having a leading edge and a trailing edge. A flap is positioned with its leading edge behind the trailing edge of the strut. The flap is pivotable about an axis near its leading edge such that the flap is pivotable from a zero deflection position to a fully deflected position. In the zero deflection position, the leading edge and trailing edge of the flap are substantially aligned with and masked behind the leading edge and the trailing edge of the strut. In the fully deflected position, the flap extends at an angle (e.g. 45°) relative to the strut, with the leading edge of the flap adjacent the trailing edge of the strut and the trailing edge of the flap is deflected substantially into the airflow, such that a side surface of the flap deflects airflow into the engine.  
         [0004]     Generally, the zero deflection position is used during high speeds, while the fully deflected position is used during engine start up. Thus, many prior designs have been optimized only for the zero deflection position without much consideration of the inlet guide vane in the deflected position. As a result, the known inlet guide vanes may cause separation of the air flow from the flap, which results in a turbulent and even pulsating flow into the engine. This increases wear on the components downstream of the inlet guide vane. In part, some of the problems in the known inlet guide vanes occur because of the gap between the trailing edge of the strut and the leading edge of the flap. Air flowing into the gap loses momentum and then flows out unevenly, disrupting the air flow on the surface of the flap.  
         [0005]     Sometimes it is desirable to have an exit turning angle that is positive at the outer end and negative at the inner end of the flap at the zero deflection position. This exit angle is in the form of some prescribed inlet angle distribution along the span of a downstream airfoil. Some known flaps have a camber that varies along its span, such that the camber of the flap switches from negative (at the inner end) to positive (at the outer end). This type of flap may have trouble when the flap is deflected to a closed position, where the outer end has positive camber in the direction of flap deflection while the inner end has negative camber opposite to the direction of flap deflection. This can lead to high losses and flow separations.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides an inlet guide vane that avoids separation of flow even at high incidence angles. Generally, the strut and the flap are designed together so that low momentum air in the gap between the strut and the flap will be energized and entrained in the boundary layer of the flap. The airflow from the gap will remain attached to the flap to improve the flow from the flap.  
         [0007]     In one embodiment, the strut has opposite side surfaces that are continuously curved to provide a controlled velocity distribution at the trailing edge of the strut. The flap has a leading edge aligned behind the trailing edge of the strut. The flap includes a pressure side surface having a peak spaced away from the leading edge. A suction side surface of the flap has a peak spaced further away from the leading edge than the peak on the pressure side surface, to provide a more gradual acceleration of the airflow.  
         [0008]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a sectional view of one example turbine engine in which the inlet guide vane of the present invention can be used.  
         [0010]      FIG. 2  is a section taken along lines  2 - 2  of  FIG. 1 .  
         [0011]      FIG. 3  is a view similar to  FIG. 2  with the flap in the fully deflected position.  
         [0012]      FIG. 4  is an enlarged view of the strut in  FIG. 2 .  
         [0013]      FIG. 5  is an enlarged view of the flap of  FIG. 2 .  
         [0014]      FIG. 6  is a series of radially-spaced section views of a second embodiment of the inlet guide vane.  
         [0015]      FIG. 7  illustrates an enlarged view of the flap at 10% section view of  FIG. 6 .  
         [0016]      FIG. 8  illustrates a second alternate flap.  
         [0017]      FIG. 8A  schematically illustrates a variation of the second alternate flap, from a trailing edge perspective view.  
         [0018]      FIG. 9  is a perspective view of the upper leading edge of a third alternate flap.  
         [0019]      FIG. 10  illustrates an inlet guide vane according to the present invention with an optional upper edge/end wall junction that could be used in any of the embodiments of this application. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]      FIG. 1  shows a gas turbine engine  10  circumferentially disposed about an engine centerline or axial centerline axis  12 . The engine  10  includes a compressor  16 , a combustion section  18  and a turbine  20 . As is well known, air compressed in the compressor  16  is mixed with fuel that is burned in the combustion section  18  and expands in the turbine  20 . The turbine  20  rotates in response to the expansion driving the compressor  16 .  
         [0021]     A plurality of inlet guide vanes  30  (one shown) are disposed about the centerline axis  12  in front of the compressor  16 . Each in the inlet guide vanes  30  includes a strut  32  (a fixed airfoil) and a flap  34  (variable incidence airfoil). The flap  34  is pivotable about an axis  36  near the strut  32 . Although the inlet guide vane  30  of the present invention is shown and used with a particular type of gas turbine engine  10 , the invention is not so limited, and can be used with any known gas turbine engine type.  
         [0022]      FIG. 2  is section view taken along line  2 - 2  of  FIG. 1  through the inlet guide vane  30  when the inlet guide vane  30  is in the zero deflection position. The inlet guide vane  30  has a centerline  40 , which in this particular embodiment evenly divides a symmetrical strut  32 . However, in particular applications, the strut  32  may not be symmetrical. The strut  32  includes a leading edge  42  and a trailing edge  44 . Opposite side surfaces  46 ,  48  extend from the leading edge  42  to the trailing edge  44 . The side surfaces  46 ,  48  each have continuous curvature from the leading edge  42  to the trailing edge  44  giving the strut  32  what is generally an airfoil shape, or more particularly, an airfoil shape having a truncated trailing edge  44 .  
         [0023]     As shown in the example embodiment, the flap  34  need not be symmetrical about the centerline  40  at all. The flap  34  includes a leading edge  52  and a trailing edge  54  which as shown in this embodiment may both be located on the same side of the centerline  40  in the zero deflection position. The flap  34  includes a pressure side surface  56  and a suction side surface  58  between the leading edge  52  and the trailing edge  54 . The pivot axis  36  of the flap  34  may or may not be located on the centerline  40 . In this particular embodiment, the pivot axis  36  is closer to the pressure side surface  56  of the flap  34  (i.e. the direction toward which the flap  34  can pivot); however, the particular location will depend upon each particular application. The leading edge  52  of the flap  34  is separated from the trailing edge  44  of the strut  32  by a gap  59 .  
         [0024]     The inlet guide vane  30  is shown with the flap  34  pivoted to the fully deflected position in  FIG. 3 . As shown, the leading edge  52  of the flap remains masked behind the trailing edge  44  of the strut  32  while the side surface  56  and trailing edge  54  of the flap  34  project into the air flow to control and deflect the air flow.  
         [0025]     Enlarged views of the strut  32  and the flap  34  are shown in  FIGS. 4 and 5 , respectively. Details of the strut  32  and flap  34  will be described in more detail with respect to those figures; however, any of the particular details are specific to a particular application, and it is the general design principles set forth herein that are primarily the subject of this invention, although the specific details of these designs maybe independently patentable as well.  
         [0026]     Referring to  FIG. 4 , the side surfaces  46 ,  48  each have continuous curvature from the leading edge  42  to the trailing edge  44  giving the strut  32  what is generally an airfoil shape, or more particularly in this example, an airfoil shape having a truncated trailing edge  44 . The side surfaces  46 ,  48  curve outwardly from the leading edge  42  to a maximum thickness of the strut  32  generally at a midpoint and then taper in a curve convexly inwardly as they extend to the trailing edge  44 . The trailing edge  44  optionally includes a pair of protrusions or ridges  60  protruding aft from the trailing edge  44 , defining a recess  62  between the ridges  60 . The ridges  60  assist in minimizing the energy of the flow passing through the gap  59 . By slowing the flow through the gap  59 , the flow exiting the gap  59  can more easily be entrained with the boundary layer on the flap  34 .  
         [0027]     In general, the strut  32  is designed to control the velocity distribution of the airflow at the trailing edge  44 . It is optimized for incidence range, low drag, soft stall and a long favorable pressure gradient. The tapered aft section of the strut  32  provides a controlled recovery region just upstream of the gap  59  ( FIGS. 2-3 ). The thickness, camber and location of the truncation of the strut  32  are determined such that the pressure distribution will be optimized for the flap  34  ( FIGS. 2-3 ). The trailing edge thickness of the strut  32  is determined such that it will mask the leading edge  52  of the flap  34  ( FIGS. 2-3 ) throughout its incidence range.  
         [0028]      FIG. 5  illustrates the flap  34  in more detail. The pressure side surface  56  and the suction side surface  58  extend from the leading edge  52  to the trailing edge  54 . The pressure side surface  56  includes a peak thickness  68  relative to the centerline  40  that is spaced aft of the leading edge  52 . The suction side surface  58  includes a peak thickness  70  relative to the centerline  40  that is spaced aft of the leading edge  52  and aft of the peak thickness  68  of the pressure side surface  56 . Again, the exact shape will depend upon the specific application, but in the example design, the peak thickness  70  is substantially aft of the peak thickness  68 , and preferably more than twice as far from the leading edge  52 .  
         [0029]     The pressure side surface  56  curves convexly outwardly to the peak thickness  68 , then curves convexly inwardly to an approximate midpoint and then curves concavely outwardly to the trailing edge  54 . The suction side surface  58  curves convexly outwardly from the leading edge  52  across centerline  40  to the peak thickness  70  and then convexly inwardly to the trailing edge  54  across the centerline  40 , although there is minimal curve on the suction side surface  58  in the last third of the length of the flap  34 .  
         [0030]     The leading edge  52  of the flap  34  is designed such that it remains masked behind the profile of the strut  32  ( FIG. 4 ) throughout its incidence range. This minimizes the pressure differential between the accelerated flow on the pressure side of the gap  59  ( FIGS. 2-3 ) and the lower speed flow on the suction side of the gap  59 .  
         [0031]     In operation, referring to  FIG. 2 , the continuous curvature of the side surfaces  46 ,  48  of the strut  32  and the controlled deceleration of the flow at the tapered rearward portion provide a controlled velocity distribution of the flow to the leading edge  52  of the flap  34 . In the zero deflection position shown in  FIG. 2 , the airflow flows from the trailing edge  44  of the strut  32  to the leading edge  52  of the flap  34  and along the side surfaces  56 ,  58  of the flap  34 .  
         [0032]     In the fully deflected position, shown in  FIG. 3 , the peak thickness  68  of the pressure side surface  56  of the flap  34  is near the trailing edge  44  of the strut  32 . However, the peak thickness  68  is also aft of a point on the pressure side surface  56  at the intersection of an extension  69  of side surface  46  of the strut  32  and the pressure side surface  56  of the flap  34 . On the pressure side, the airflow flows from the trailing edge  44  of the strut  32 , across the gap  59  and then accelerates along the pressure side surface  56  of the flap  34  to the peak thickness  68 , thereby drawing any low momentum air out of the gap  59 . On the suction side, the airflow from the trailing edge  44  of the strut  32  flows across the gap  59 , decelerates as it turns along the flap  34  and then accelerates at a moderate rate over the long continuous convex curvature of the suction side surface  58 . Because the peak thicknesses  68 ,  70  are far enough downstream of the gap  59 , the leaked flow from the gap  59  will be accelerated and entrained in the boundary layer of the flap  34 . The camber of the flap  34  is designed to provide a velocity distribution at all desired incidences that will energize the flow through the gap  59  and remain attached to the flap  34  and deliver the desired exit air angle. The thickness of the flap  34  is determined by the passage requirements and can be thicker or thinner than the strut  32  as needed.  
         [0033]      FIG. 6  is a series of section views through an inlet guide vane  130  according to a second embodiment of the present invention. The section views are radially spaced from one another along the span of the inlet guide vane  130  at a nominal zero deflection position. The 10% section view is taken at a point 10% of the inlet guide vane&#39;s span from a radially inner edge of the inlet guide vane. The 30% section view is taken at a point 30% of the span from the inner edge, and so on.  
         [0034]     As explained above the Background, sometimes it is desirable to have an exit turning angle that is both negative (at the inner end) and positive (at the outer end) on the same flap at the zero deflection position. The flap  134  in  FIG. 6  is a “reflexed airfoil,” which gives a negative air angle for a positively cambered flap  134 . This is done by introducing a bi-camber on the flap  134  section (along the chord) instead of along the span. The camber of the flap  134  starts in one direction and then reverses towards the trailing edge  154 . The amount of bi-camber is balanced with flap sectional incidence, allowing the desired amount of negative camber at the trailing edge  154  to be “dialed” in. Therefore the overall camber stays the same for all flap  134  sections down the span. This improves flow attachment at high deflection angles. The flap  134  allows the inner end sections to be designed for balanced and optimized performance at both the zero deflection and full deflection positions. The reason this is possible is that when the flap  134  is in the zero deflection position, the last 40 or 50% of the flap  134  section is the biggest player (in minimizing drag), while when in the fully deflected position, the first 50 or 60% of the flap  134  section is the most critical to the success of the airfoil delivering the desired performance (minimal or no separation). Therefore the flap  134  has a trailing edge  154  with a good high speed camber for low loss but at the same time has good low speed high turning camber in the opposite direction for when the flap  134  is deflected. All of the design techniques described above with respect to  FIGS. 1-5  are applicable to this embodiment as well.  
         [0035]     An enlarged view of the 10% section view of the flap  134  of  FIG. 6  is shown in  FIG. 7 . The pressure side surface  156  curves convexly away from the leading edge  152  and then very gradually starts to turn concavely to the trailing edge  154  in the last third of the flap  134 . The suction side surface  158  curves convexly from the leading edge  152  and then slightly concavely to the trailing edge  154 .  
         [0036]     An optional feature is illustrated in  FIG. 8  that can be applied to any of the flaps described herein. On the flap  234  shown in  FIG. 8 , a trailing edge tab  275  protrudes normally from the pressure side surface  256  along the extreme trailing edge  254 . Although the actual dimensions of the trailing edge tab  275  will depend upon the camber, incidence range and chord of the flap  234 , the size of the trailing edge tab  275  is exaggerated in  FIG. 8  for purposes of illustration. The trailing edge tab  275  assists in the continued attachment of flow when extremely high incidence is required.  
         [0037]     More generally, the trailing edge tab  275  is on the side of maximum incidence change. Thus, in a bi-cambered flap  234   a  as shown in  FIG. 8A , the trailing edge tab  275   a  may protrude from a pressure side surface  256   a  near the trailing edge  254   a  at an inner portion of the flap  234   a , gradually disappear in the center of the flap  234   a  and gradually reappear on the suction side surface  258   a  of the flap  234   a  at a radially outer portion of the flap  234   a.    
         [0038]     Another optional feature that can be applied to any of the embodiments described herein is illustrated in  FIG. 9 . An OD hinge pivot  380  at the leading edge  352  and upper edge  353  of the flap  334  includes a low profile streamlined disk  382  having a tapered rearward portion  384 . The OD hinge pivot  380  shown in  FIG. 9  provides structural rigidity while reducing the amount of blockage introduced as compared with the previous designs where an upper portion of the leading edge angled forwardly in order to reinforce the hinge pivot.  
         [0039]      FIG. 10  illustrates another optional feature that could be used with any of the flaps disclosed herein. An inlet guide vane  430  includes a strut  432  and a flap  434  that is pivotable about a pivot axis  436 . An upper edge  488  of the flap  434  is curved convexly in a manner complementary to a spherical inner surface  490  of the end wall. The spherical inner surface  490  is defined by a hypothetical sphere having a center point at the intersection of the pivot axis  436  and the engine centerline axis  12  ( FIG. 1 ). The curve of the upper edge  488  of the flap  434  is also defined about the center point of the sphere. As a result, the gap between the upper edge  488  of the flap  434  and the spherical inner surface  490  remains constant throughout the full incidence range of the flap  434 .  
         [0040]     Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.