Abstract:
Inlet guide vanes and gas turbine engine systems involving such vanes are provided. In this regard, a representative an inlet guide vane for a gas turbine engine includes: a fixed strut; and a variable flap located downstream of the fixed strut and being movable with respect thereto; the fixed strut having a leading edge, a trailing edge and side surfaces extending between the leading edge and the trailing edge, the side surfaces being asymmetric with respect to each other.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure generally relates to gas turbine engines. 
         [0003]    2. Description of the Related Art 
         [0004]    Some gas turbine engines include variable geometry inlet guide vanes that are positioned upstream of the compressors (also known as “fans” in some implementations) of the engines. Such an inlet guide typically includes a fixed strut and a movable flap positioned adjacent to and downstream of the fixed strut. The flap can be selectively positioned to alter deflection of airflow to downstream components of the engine. Unfortunately, some positions of the flap may result in unwanted airflow separation from the surface of the flap, resulting in a turbulent airflow. Such airflow tends to increases wear on the components downstream of the inlet guide vane. 
       SUMMARY 
       [0005]    Inlet guide vanes and gas turbine engine systems involving such vanes are provided. In this regard, an exemplary embodiment of an inlet guide vane for a gas turbine engine comprises: a fixed strut; and a variable flap located downstream of the fixed strut and being movable with respect thereto; the fixed strut having a leading edge, a trailing edge and side surfaces extending between the leading edge and the trailing edge, the side surfaces being asymmetric with respect to each other. 
         [0006]    An exemplary embodiment of an inlet guide vane assembly for a gas turbine engine comprises: multiple inlet guide vanes; a first of the inlet guide vanes having a fixed strut and a variable flap; the variable flap being located downstream of the fixed strut and being movable with respect thereto; the fixed strut exhibiting chordwise asymmetry operative to reduce a tendency of gas flowing along surfaces of the inlet guide vane to separate therefrom. 
         [0007]    An exemplary embodiment of a gas turbine engine comprises: a compressor section having an inlet guide vane assembly, a set of rotatable blades and a set of stationary vanes; the inlet guide vane assembly being located upstream of the set of rotatable blades and the set of stationary vanes, the inlet guide vane assembly having multiple guide vanes; a first of the guide vanes having a fixed strut and a variable flap, the variable flap being located downstream of the fixed strut and being movable with respect thereto, the fixed strut having a leading edge, a trailing edge and side surfaces extending between the leading edge and the trailing edge, the side surfaces being asymmetric with respect to each other. 
         [0008]    Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0010]      FIG. 1  is a schematic diagram depicting a portion of an exemplary embodiment of a gas turbine engine. 
           [0011]      FIG. 2  is a schematic diagram depicting an inlet guide vane of the embodiment of  FIG. 1 , as viewed along section line  2 - 2  with the flap in a nominal position. 
           [0012]      FIG. 3  is a schematic diagram depicting an inlet guide vane of the embodiment of  FIG. 1 , as viewed along section line  2 - 2  with the flap in a deflected position. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Inlet guide vanes and gas turbine engine systems involving such vanes are provided, several exemplary embodiments of which will be described in detail. In this regard, some embodiments involve the use of a fixed strut that exhibits chordwise asymmetry (i.e., the fixed strut is asymmetric with respect to the chord line, which extends from the leading edge to the trailing edge of the strut). Such asymmetry may reduce a tendency of gas flowing along surfaces of the inlet guide vane to separate, thus maintaining laminar flow along the surfaces. In some embodiments, the chordwise asymmetry is expressed by an aft portion of the fixed strut (which is located adjacent to the suction side surface of a downstream flap) that enables turning of gas prior to the gas reaching the flap (e.g., turning with respect to the axial flow direction). As such, some of the turning of the gas is accomplished by the strut, thereby potentially resulting in more overall turning of the gas. Regardless of the degree of turning, less of the turning is provided by the flap since some of the turning is provided by the strut itself. This is in contrast to conventional vanes, which perform the turning of gasses entirely with the flaps. 
         [0014]    In this regard, reference is made to the schematic diagram of  FIG. 1 , which depicts a portion of an exemplary embodiment of a gas turbine engine. As shown in  FIG. 1 , engine  100  is depicted as a turbojet engine that incorporates a compressor section  102 . Notably, although various other components are not depicted, a combustion section  104  and a turbine section  106  are located downstream of the compressor section. It should also be noted that, although depicted as a turbojet gas turbine engine, it is to be understood that the concepts described herein are not limited to use with turbojets as the teachings may be applied to other types of gas turbine engines. 
         [0015]    Inlet guide vanes (e.g., vane  110 ) are positioned radially about the centerline  112  of the engine upstream of a compressor  114 , which in this embodiment is a low-pressure compressor. Each of the inlet guide vanes includes a fixed strut (e.g., fixed strut  116 ) and a variable flap (e.g., variable flap  118 ). The flap is pivotable about an axis to provide a range of positions for variably deflecting airflow into the downstream components of the engine, e.g., the compressor  114 . 
         [0016]    As shown in  FIG. 2 , which is a schematic, section view taken along line  2 - 2  of  FIG. 1 , strut  116  has a chordline  120  (depicted in dashed lines), which in this embodiment evenly divides a symmetrical front portion of strut. Strut  116  includes a leading edge  122 , a trailing edge  124 , and opposing side surfaces  126 ,  128  that extend between the leading edge and the trailing edge. Notably, an aft portion  130  of the strut, which in this embodiment is aft of the location of maximum thickness  132 , exhibits chordwise asymmetry. Specifically, side surface  126  exhibits negative camber in a vicinity of flap  118 . In some embodiments, the negative camber begins at between approximately 25% and approximately 95% chord of the fixed strut, preferably between approximately 50% and approximately 80% chord of the fixed strut. 
         [0017]    Flap  118  includes a leading edge  140 , a trailing edge  142 , a pressure side surface  144  and a suction side surface  146 . The leading edge of the flap is separate from the trailing edge of the strut by a gap  148 . The flap is pivotable about an axis  149  to exhibit a range of positions between a nominal or zero deflection position (shown in  FIG. 2 ), at which a minimum deflection is imparted to gas flowing over the variable flap, and a maximum deflection position (shown in  FIG. 3 ), at which a maximum deflection is imparted to gas flowing over the variable flap. 
         [0018]    In all deflection positions, the leading edge of the flap of this embodiment is masked behind the trailing edge of the strut. In some embodiments, this is accomplished even though the thickness of the fixed strut at the trailing edge is between approximately 90% and approximately 50% of a maximum thickness of the variable flap. 
         [0019]    However, at the nominal position ( FIG. 2 ), the suction side surface  146  of the flap is not masked by the strut as shown by the exemplary streamline  150 , which deflects inwardly in the vicinity of gap  148 . In contrast, at the maximum deflection position ( FIG. 3 ), the suction side surface  146  of the flap is masked by the strut as evidenced by the exemplary streamline  160 , which exhibits a smooth, continuous curve in the vicinity of gap  148 . Notably, flap thickness can be based, at least in part, on passage requirements and can be thicker or thinner than the strut as needed. 
         [0020]    In the nominal position shown in  FIG. 2 , airflow flows along the opposing side surfaces  126 , 128  of the strut. As the airflow along surface  126  approaches the gap  148 , the airflow flows inwardly toward the gap due to the negative camber of the aft portion  130  of the strut. Thereafter, the airflow flows along the suction side  146  of the flap until departing in a vicinity of the trailing edge  142 . The airflow along side surface  128  of the strut continues toward trailing edge  124 , across the gap  148 , and then along pressure side surface  144  of the flap. Notably, the flap does not contribute to or detract from performance of the strut in the nominal position. 
         [0021]    In a deflected position, such as the maximum deflection position of  FIG. 3 , airflow flowing across side surface  126  of the strut is turned between approximately 0.5 degrees and approximately 10 degrees (preferably between approximately 1 degree and approximately 5 degrees) prior to the gas flow reaching the flap. Thereafter, the airflow flows along the suction side  146  of the flap until departing in a vicinity of the trailing edge. In some embodiments, up to approximately 60 degrees of airflow deflection, for example, can be provided without airflow separation from the vane. 
         [0022]    By providing at least some of the turning of the airflow using the strut (i.e., prior to the airflow reaching the flap), the effective chord length of the flap is increased. In some embodiments, this can facilitate the use of a shorter flap, which correspondingly could require a smaller deflection force to achieve full deflection. In other embodiments, such as those in which axial restrictions limit the use of longer flaps, turning accomplished by the strut can provide for increased turning without flow separation. 
         [0023]    It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.