Abstract:
Non-uniform variable stator vanes for a single stage of a gas turbine engine stage include non-uniform airfoils with a non-uniformity between airfoils of first and second portions of the stator vanes. The variable stator vanes may further include all outer buttons, from which the airfoils inwardly extend, in all of the variable stator vanes being equally sized and shaped and the same all inner buttons if used. The airfoils in the first and second portions may be counter-clockwise and clockwise biased respectively with respect to a nominal airfoil position. The airfoils in the first and second portions may be counter-clockwise and clockwise leaned respectively with respect to the nominal airfoil position. Outer ends of the airfoils in the first and second portions may be counter-clockwise and clockwise shifted respectively with respect to the nominal airfoil position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    This invention relates to aircraft gas turbine engines and, particularly, to variable stator vanes. 
         [0003]    2. Background Information 
         [0004]    Variable stator vanes (VSVs) are commonly used in aircraft gas turbine engine compressors and fans and in some turbine designs. Non-rotating or stationary stator vanes typically are placed downstream or upstream of rotor blades of the fans, compressors, and turbines. These vanes reduce the tangential flow component leaving the rotors, thereby, increasing the static pressure of the fluid and setting the flow angle to a level appropriate for the downstream rotor. 
         [0005]    Airfoils in variable and non-variable vanes have a series of natural frequencies associated with them. More specifically, each airfoil produces a wake in an air stream that is felt as a pulse by a passing airfoil. The combination of the number of stator vanes and the rotational speed of the compressor may coincide with a natural frequency of the rotor blades. The combination of the number of stator vane wakes (pulses) and the rotational speed of the compressor creates a stimulus that may coincide with a natural frequency of the rotor blades. It is highly desirable to keep the majority of the airfoil natural frequencies outside of the designed engine operating range. 
         [0006]    Non-uniform vane spacing (NUVS) designs have been developed to reduce induced rotor blade vibrations. NUVS designs vary the vane spacing around the circumference of the engine casing to facilitate avoidance of rotor blade and stator vane natural frequencies or to reduce the amplitude of rotor blade resonant response at these frequencies. More specifically, within such designs the number of stator vanes is varied in one or more sectors of the stator vane assembly. Although the stator vane spacing may vary from one sector to the next, the stator vanes within each sector remain equally spaced relative to each other, and/or are designed with an equal pitch. The variation in vane spacing or pitch between stator vane sectors facilitates changing the frequency of the vane wakes to reduce the vibration response induced in adjacent rotor blades. 
         [0007]    Due to the large range of operating conditions experienced by an axial flow compressor over a typical operating cycle, flow rates and rotational speeds of the compressor also vary widely. This results in large shifts in the absolute flow angle entering the stator vanes. To allow the vanes to accommodate these shifts in flow angle without encountering high loss or flow separation, circumferential rows of variable stator vanes are constructed so that the vanes can be rotated about their radial (or approximately radial) axis. 
         [0008]    Generally, variable stator vanes (VSVs) have spindles through their rotational axis that penetrate the casing, allowing the vanes to be rotated using an actuation mechanism. At the flowpath, there is typically radially inner and outer buttons of material around the spindle which rotates along with the vane. Because there is a large pressure gradient between the pressure and suction sides of the vane, leakage flow is driven across this gap, resulting in reduced fluid turning and higher loss at the endwalls. This leakage flow also causes flow non-uniformities (i.e. wakes) at the adjacent rotor blades, which may excite these blades causing potentially damaging vibrations in the rotor blades. Conventional VSV buttons typically have diameters equal to or slightly less than the pitchwise spacing between vanes at their respective locations. 
         [0009]    It is particularly difficult to implement NUVS designs for VSVs of existing engine lines or families because of the associated hardware and casing designs that include equiangularly spaced holes in the casings for the buttons. It is near impossible to retrofit with NUVS designs for VSVs incorporating different sector spacing of different spacing between upper and lower sets of VSVs. Thus, it is highly desirable to provide a VSV with NUVS having has equidistant or equiangular spacing between the radially inner buttons and between the radially outer buttons and between the spindles around the casing. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0010]    A plurality of same stage variable stator vanes includes non-uniform same stage variable stator vanes having non-uniform airfoils with at least first and second portions of the plurality of non-uniform same stage variable stator vanes. Each of the variable stator vanes includes a rotational axis. Each of the airfoils extends inwardly from an outer button centered about a rotational axis. Each of the airfoils may be cantilevered from and extend inwardly from the outer button or each of the airfoils may be disposed between spaced apart outer and inner buttons. An outer spindle extends outwardly from the outer button and for the embodiment of the variable stator vane with both outer and inner buttons an inner spindle extends inwardly from the inner button. The non-uniform same stage variable stator vanes have a non-uniformity between airfoils of the variable stator vanes of the first portions and airfoils of the variable stator vanes of the second portion. 
         [0011]    All of the outer buttons in all of the variable stator vanes may be equally sized and shaped and if used all of the inner buttons in all of the variable stator vanes may be equally sized and shaped. 
         [0012]    The non-uniformity may include the airfoils in the first portion of the plurality of variable stator vanes being counter-clockwise biased with respect to a nominal airfoil position and the airfoils in the second portion of the plurality of variable stator vanes being clockwise biased with respect to the nominal airfoil position. 
         [0013]    The non-uniformity may include the airfoils in the first portion of the plurality of variable stator vanes being counter-clockwise leaned with respect to a nominal airfoil position and the airfoils in the second portion of the plurality of variable stator vanes being clockwise leaned with respect to the nominal airfoil position. The airfoils in the first and second portions may be counter-clockwise and clockwise leaned about inner ends of the airfoils respectively and each of the inner ends equally positioned with respect to the rotational axis of each respective vane. 
         [0014]    The airfoils may extend between airfoil outer and inner ends of the airfoils with the non-uniformity including the outer ends of the airfoils in the first portion of the plurality of variable stator vanes being counter-clockwise shifted with respect to a nominal airfoil position and the outer ends of the airfoils in the second portion of the plurality of variable stator vanes being clockwise shifted with respect to the nominal airfoil position. 
         [0015]    A gas turbine engine assembly includes a gas turbine engine casing radially outwardly supporting a variable vane assembly including at least one circular row of non-uniform same stage variable stator vanes having non-uniform airfoils. Each of the airfoils is disposed between spaced apart outer and inner buttons centered about a rotational axis of each of the variable stator vanes and each of the variable stator vanes includes an outer spindle extending outwardly from the outer button and an inner spindle extending inwardly from the inner button. The outer spindles are rotatably disposed through outer trunnions mounted in outer opening in the casing. At least first and second portions of the plurality of same stage variable stator vanes include a non-uniformity between airfoils of the variable stator vanes of the first portions and airfoils of the variable stator vanes of the second portion. All of the outer buttons in all of the variable stator vanes may be equally sized and shaped and all of the inner buttons in all of the variable stator vanes being equally sized and shaped and the outer opening equiangularly spaced around the casing. 
         [0016]    The gas turbine engine casing may be the same or have the same design as a previously manufactured gas turbine engine or a family of gas turbine engines with uniform same stage variable stator vanes having uniform airfoils. 
         [0017]    A method for manufacturing a gas turbine engine assembly provides a gas turbine engine casing radially outwardly supporting a variable vane assembly including at least one circular row of non-uniform same stage variable stator vanes. The method includes providing counter-clockwise biased airfoils in a first one of upper and lower sectors of a single stage of non-uniform same stage variable stator vanes and clockwise biased airfoils in a second one of the upper and lower sectors of the single stage of non-uniform same stage variable stator vanes. The method further includes manufacturing the vanes with the counter-clockwise biased and the clockwise biased airfoils disposed between spaced apart outer and inner buttons centered about rotational axis of each of the variable stator vanes and manufacturing the vanes with each of the variable stator vanes including an outer spindle extending outwardly from the outer button and an inner spindle extending inwardly from the inner button. The method further provides assembling the outer spindles rotatably disposed through outer trunnions mounted in outer opening in a casing. The method may include the gas turbine engine casing having the same or the same design as a previously manufactured gas turbine engine or a family of gas turbine engines with uniform same stage variable stator vanes having uniform airfoils. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a sectional view illustration of a portion of a gas turbine engine high pressure compressor having variable stator vanes with non-uniform vane spacing (NUVS). 
           [0019]      FIG. 2  is a diagrammatical view illustration of a high pressure compressor stage with the variable stator vanes with non-uniform vane spacing (NUVS) in the high pressure compressor illustrated in  FIG. 1 . 
           [0020]      FIG. 3  is an enlarged diagrammatical view illustration of clockwise and counter-clockwise leaned airfoils of the variable stator vanes illustrated in  FIG. 2 . 
           [0021]      FIG. 4  is a perspective view illustration of a clockwise leaned airfoil illustrated in  FIG. 3 . 
           [0022]      FIG. 5  is a perspective view illustration of a counter-clockwise leaned airfoil illustrated in  FIG. 3 . 
           [0023]      FIG. 6  is a perspective view illustration of two halves of a gas turbine engine split compressor casing with outer trunnion holes to accommodate trunnions of the variable stator vanes illustrated in  FIG. 1 . 
           [0024]      FIG. 7  is an enlarged diagrammatical view illustration of an alternative arrangement of clockwise and counter-clockwise leaned airfoils of the variable stator vanes illustrated in  FIG. 3  having circumferentially alternating clockwise and counter-clockwise leaned airfoils. 
           [0025]      FIG. 8  is a perspective view illustration of a variable stator vane with a cantilevered clockwise leaned airfoil. 
           [0026]      FIG. 9  is a perspective view illustration of a variable stator vane with a cantilevered counter-clockwise leaned airfoil. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Illustrated in  FIG. 1  is a portion of an exemplary turbofan gas turbine engine high pressure compressor  10  which is axisymmetrical about a longitudinal or axial centerline axis  12 . Circular first and second rows  11 ,  13  of variable stator vanes  15  with non-uniform vane spacing (NUVS) are disposed in the compressor  10  and used to optimize the direction at which gases flowing downstream D through the compressor  10  enter first and second rows  17 ,  18  of rotatable blades  16 . Though the exemplary embodiment of the variable stator vanes  15  with non-uniform vane spacing disclosed herein is for a high pressure compressor, these VSV&#39;s may be used in other compressor sections and in fan and turbine sections of a gas turbine engine as well. A compressor casing  61  radially outwardly supports variable stator vane assemblies  56  which include the variable stator vanes  15 . The non-uniform variable stator vanes  15  illustrated herein have non-uniform airfoils  31 . 
         [0028]    Referring to  FIGS. 1 ,  4 , and  5 , each variable stator vane assembly  56  includes a plurality of variable stator vanes  15 . Each variable stator vane  15  is pivotable or rotatable about a rotational axis  20 . Each variable stator vane  15  has an airfoil  31  disposed between spaced apart outer and inner buttons  32 ,  33 . The airfoil  31  extends inwardly from an airfoil outer end  72  to an airfoil inner end  73  along a span S of the airfoil. The airfoil outer and inner ends  72 ,  73  are mounted on the outer and inner buttons  32 ,  33  respectively. An outer spindle  34  extends outwardly from the outer button  32  and an inner spindle  35  extends inwardly from the inner button  33 . The outer and inner spindles  34 ,  35  are rotatably supported in outer and inner trunnions  36 ,  37  and centered and rotatable about the rotational axis  20 . 
         [0029]    The outer spindle  34  is rotatably disposed through the outer trunnion  36  which, in turn, is mounted in an outer opening  78  in the casing  61 . The outer openings  78  illustrated herein are equiangularly circumferentially spaced around the casing  61  at a constant radius about the axial centerline axis  12 . The inner spindle  35  is rotatably disposed through the inner trunnion  37  which, in turn, is mounted in an inner opening  79  in an inner ring  81  which is spaced radially inwardly of the casing  61 . A lever arm  80  extends from the outer spindle  34  and is linked to an actuation ring  82  for rotating or pivoting and setting the flow angle of the variable stator vanes  15 . 
         [0030]    The outer and inner buttons  32 ,  33  are rotatably disposed in outer and inner circular recesses  42 ,  43  in the casing  61  and the inner ring  81  respectively. Each airfoil  31  has an airfoil leading edge LE upstream U of an airfoil trailing edges TE and pressure and suction sides PS, SS. 
         [0031]    Referring to  FIGS. 4-5 , the outer and inner buttons  32 ,  33  each have substantially circular edges  52  with a flat spot  53 . 
         [0032]    Each of the circular edges  52  of outer and inner buttons  32 ,  33  define a circular perimeter  22  within which each button rotates about the rotational axis  20 . The circular perimeter  22  is circumscribed about the rotational axis  20  at the button radius RB from the rotational axis  20 . A recess  58  is cut out or recessed in from the perimeter  22 . The recesses  58  are designed to maximize the area A of the button while accommodating a large turning angle (not shown) of the variable stator vanes  15 . 
         [0033]    In order to reduce induced rotor blade vibration amplitudes, at least one of the variable stator vane assemblies  56  is a non-uniform variable stator vane assembly  57 . The non-uniform variable stator vane assembly  57  includes different vanes in variable stator vane first and second or upper and lower sectors  62 ,  64  to facilitate avoidance of rotor blade and stator vane natural frequencies or to reduce the amplitude of rotor blade resonant response at these frequencies. The non-uniformity between the variable stator vanes  15  in the upper and lower sectors  62 ,  64  facilitates changing the frequency of the vane wakes to reduce the vibration response induced in adjacent rotor blades. 
         [0034]    The non-uniformity between the variable stator vanes  15  in the upper and lower sectors  62 ,  64  disclosed herein is different upper and lower leans of the airfoils  31  of the variable stator vanes  15  in the upper and lower sectors  62 ,  64  respectively. The airfoils  31  in one of the upper and lower sectors  62 ,  64  are leaned circumferentially more in the clockwise direction CW and airfoils  31  in another of the upper and lower sectors  62 ,  64  are leaned circumferentially more in the counter-clockwise direction CCW. All the airfoils  31  may still be leaned in either the clockwise or the counter-clockwise directions they are just biased more in one or the other circumferential directions. Though two sectors of 180 degrees each are illustrated herein, more sectors may be used and so may more airfoil lean angles. Within each of the upper and lower sectors  62 ,  64 , the variable stator vanes  15  are substantially identical and uniform and, more particularly, uniformally circumferentially leaned. One embodiment of the number of sectors includes only one vane in each sector and each pair  28  of adjacent vanes has two different airfoil lean angles illustrated as clockwise and counter-clockwise airfoil lean angles  24 ,  26  as illustrated in  FIG. 7 . 
         [0035]    One exemplary embodiment of the non-uniform variable stator vane assembly  57  illustrated herein includes different upper and lower airfoil lean angles  83 ,  84  of the airfoils  31  of the variable stator vanes  15  in the upper and lower sectors  62 ,  64  respectively as illustrated in  FIG. 3 . For purpose of illustration, the airfoils  31  of the variable stator vanes  15  in the upper and lower sectors  62 ,  64  are leaned in the counter-clockwise and clockwise directions CC, CCW at the upper and lower airfoil lean angles  83 ,  84  respectively as illustrated in  FIG. 3 . The airfoils  31  in the upper and lower sectors  62 ,  64  are leaned in the counter-clockwise and clockwise directions CC, CCW with respect to a nominal airfoil lean angle  88  which may be 0 degrees or another angle. By way of example only, the lean angles may be about 17% of an acute angle  87  between the airfoil outer ends  72  of adjacent airfoils  31  as measured along engine radii R extending radially outwardly from the engine axial centerline axis  12  to the airfoil outer ends  72  on the outer buttons  32 . 
         [0036]    Referring to  FIGS. 3-5 , the upper and lower airfoil lean angles  83 ,  84  of the airfoil  31  may be defined by upper and lower stacking axes illustrated by upper and lower stacking axes  85 ,  86  of the airfoils  31  in the upper and lower sectors  62 ,  64  respectively. A linear stacking axis may be described as a line connecting airfoil cross section center of gravities (CGs) at the airfoil outer and inner ends  72 ,  73  of an unleaned nominal airfoil  30  and counter-clockwise and clockwise shifted or leaned airfoils  45 ,  47  ( FIGS. 3-5 ) at the outer and inner buttons  32 ,  33  respectively of the vanes. Lean is a rotation of the airfoil  31  about the inner end  73  of the airfoil  31  causing the stacking axis to diverge from the engine radius R measured from the engine axial centerline axis  12 . 
         [0037]    A bowed or arcuate stacking axis may be defined by the center of gravities of the several radial sections of each airfoil, or in any other conventional manner such as, by the stacking of the midchord points thereof. Stacking axis has also been defined as representing a locus of center of gravities of transverse sections of an airfoil portion of the blade and may be linear or non-linear. 
         [0038]    Another means for providing non-uniformity between the variable stator vanes  15  in the upper and lower sectors  62 ,  64  is illustrated in  FIGS. 4 and 5 . The means includes shifting the airfoil outer ends  72  from a nominal airfoil position  66  illustrated in dashed line to counter-clockwise and clockwise positions illustrated in solid line in the different sectors as illustrated in  FIGS. 4 and 5  respectively. A nominal airfoil  31  is illustrated in dashed line counter in  FIGS. 4 and 5  and counter-clockwise and clockwise shifted or leaned airfoils  45 ,  47  are illustrated in  FIGS. 4 and 5  respectively. The inner ends  73  of the counter-clockwise and clockwise shifted or leaned airfoils  45 ,  47  remain the same as the inner end  73  of the nominal airfoil  31 . Counter-clockwise and clockwise biased airfoils  45 ,  47  is a broader description of the non-uniformity. The nominal airfoil position  66  illustrated herein is between the counter-clockwise and clockwise biased airfoils  45 ,  47 . 
         [0039]    All the variable stator vanes  15  in the upper sector  62  may be identical and all the variable stator vanes  15  in the lower sector  64  may be identical wherein the difference between the two sets of the variable stator vanes  15  is the counter-clockwise and clockwise biased airfoils  45 ,  47 . 
         [0040]    The shifting or leaning of the airfoils or other non-uniformity between the variable stator vanes  15  in the upper and lower sectors  62 ,  64  may thus be provided without changing the location size or shape of the outer and inner buttons  32 ,  33 , the outer spindle and inner spindles  34 ,  35 , the outer and inner trunnions  36 ,  37 , and the outer openings  78  in the casing  61  illustrated in  FIG. 6 . The span S of the airfoils defines a radial distance between the outer and inner buttons  32 ,  33  of the variable stator vanes  15  and may also all be the same. Thus, the non-uniformity between the variable stator vanes  15  in different sectors (two or more) can be easily designed and manufactured for existing cases and engines with a minimal change. 
         [0041]    Illustrated in  FIGS. 8 and 9  are variable stator vanes  15  having cantilevered airfoils  90  cantilevered from and extending radially inwardly or downwardly from outer buttons  32  and having no inner buttons. Each cantilevered airfoil  90  extends inwardly from an airfoil outer end  72  to an airfoil inner end  73  along a span S of the airfoil and the inner end  73  is a free end. The airfoil outer end  72  is mounted on the outer button  32 . An outer spindle  34  extends outwardly from the outer button  32 . The outer spindle  34  is rotatably supported in an outer trunnion  36  and centered and rotatable about the rotational axis  20 . 
         [0042]    The cantilevered airfoils  90  may be defined by upper and lower stacking axes illustrated by upper and lower stacking axes  85 ,  86  of the airfoils  31  in the upper and lower sectors  62 ,  64  respectively. A linear stacking axis may be described as a line connecting airfoil cross section center of gravities (CGs) at the airfoil outer and inner ends  72 ,  73  of an unleaned nominal cantilevered airfoil  90  and counter-clockwise and clockwise shifted or leaned cantilevered airfoils  92 ,  94  ( FIGS. 8-9 ). Lean is a rotation of the unleaned cantilevered airfoils  90  about the inner end  73  causing the stacking axis to diverge from the engine radius R measured from the engine axial centerline axis  12 . 
         [0043]    While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein and, it is therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims.