Abstract:
A variable inlet guide vane arrangement for a compressor includes a case defining an inlet of the compressor; at least one vane support coaxially disposed within the case; a plurality of vanes circumferentially disposed around the circumference of the case, each vane being pivotally mounted between the case and the at least one vane support; an actuator mechanism configured to pivot at least some of the plurality of vanes in an asymmetrical pattern around the circumference of the case. A method of controlling a variable inlet guide vane arrangement for a compressor includes pivoting at least some of the plurality of vanes in an asymmetrical pattern around the circumference of the case.

Description:
[0001]    This application is a divisional of U.S. application Ser. No. 12/689,656, filed Jan. 19, 2010, the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to variable inlet guide vanes used to control the flow entering a compressor, for example a compressor of a gas turbine engine. 
       BACKGROUND OF THE INVENTION 
       [0003]    A turbofan gas turbine engine used for powering an aircraft in flight typically includes, in serial flow communication, a fan, a low pressure compressor or booster, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The combustor generates combustion gases that are channeled in succession to the high pressure turbine where they are expanded to drive the high pressure turbine, and then to the low pressure turbine where they are further expanded to drive the low pressure turbine. The high pressure turbine is drivingly connected to the high pressure compressor via a first rotor shaft, and the low pressure turbine is drivingly connected to both the fan and the booster via a second rotor shaft. 
         [0004]    The high pressure compressor typically includes a series of stator vane stages used to compress air for engine and aircraft use. The first compressor stage adjacent to the booster is the inlet guide vane stage formed of a plurality of circumferentially arranged cantilevered inlet guide vanes. The inlet guide vanes may be actuated through a control system so as to optimize air flow for power and stall avoidance purposes. The guide vanes are retained between a stator case and an inner vane shroud. The stator case is coupled to the engine case. The space between the stator case and the shroud defines the volume of air passing through the high pressure compressor. The shroud provides an aerodynamic flowpath boundary of the high pressure compressor. 
         [0005]    In some engines, the inlet guide vanes, as well as other downstream stator vanes, are variably actuated through the operation of one or more controllable vane actuators. An outer trunnion or spindle of the vane passes through the stator case and is coupled to a lever arm. The lever arm is coupled to an actuation ring that is connected to a vane actuator. One or more vane actuators effect movement to the series of circumferentially arranged stator vanes of each compressor stage. The vane is retained to the stator case through a combination of bushings, washers, and a lock nut that is threaded onto the outer trunnion. 
         [0006]    The variable guide vanes are used to control the flow entering the compressor and are scheduled to open and close as a function of flow demand. At low flow conditions, the variable guide vanes can operate in a separated flow condition, while at higher flow conditions the variable guide vanes operate in a non-separated flow condition. During the movement of the variable guide vanes along the opening/closing schedule there is a region where the flow begins to separate. This region is defined as the “onset of separation.” Due to inlet distortions, flow velocities are non-uniform. This non-uniformity can cause differences in when each individual vane reaches the onset of separation. The circumferential pattern associated with this condition will drive strong harmonic stimuli which is a source of excitation for rotating blades susceptible to these excitations. This stimuli may result in strong harmonic content in regions where blade resonances reside, thus placing vibratory stresses on the blades. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    According to one embodiment of the invention, a variable inlet guide vane arrangement for a compressor comprises a case defining an inlet of the compressor; at least one vane support coaxially disposed within the case; a plurality of vanes circumferentially disposed around the circumference of the case, each vane being pivotally mounted between the case and the at least one vane support; and an actuator mechanism configured to pivot at least some of the plurality of vanes in an asymmetrical pattern around the circumference of the case. 
         [0008]    According to another embodiment of the invention, a method is provided for controlling a variable inlet guide vane arrangement for a compressor comprising a case defining an inlet of the compressor, at least one vane support coaxially disposed within the case, a plurality of vanes circumferentially disposed around the circumference of the case, each vane being pivotally mounted between the case and the at least one vane support, and an actuator mechanism configured to pivot at least some of the plurality of vanes in an asymmetrical pattern around the circumference of the case. The method comprises pivoting at least some of the plurality of vanes in an asymmetrical pattern around the circumference of the case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a partial schematic cross-sectional view of a turbofan engine incorporating an embodiment of an inlet guide vane control system; 
           [0010]      FIG. 2  is a partial cut-away perspective view of the high pressure compressor section of the engine of  FIG. 1 ; 
           [0011]      FIG. 3  is a partial exploded perspective view of the inlet guide vane control system of the engine of  FIG. 1 ; 
           [0012]      FIG. 4  is a side view of an inlet guide vane and a vane-to-shroud coupling; and 
           [0013]      FIGS. 5 and 6  schematically illustrate an inlet guide vane arrangement and actuator mechanism according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to the drawings, wherein identical reference numerals denote the same elements,  FIG. 1  illustrates a longitudinal cross-sectional view of a turbofan engine  10 . The engine  10  includes, in serial axial flow communication about a longitudinal centerline axis  12 , a fan  14 , a booster  16 , a high pressure compressor  18 , a combustor  20 , a high pressure turbine  22 , and a low pressure turbine  24 . The high pressure turbine  22  is drivingly connected to the high pressure compressor  18  with a first rotor shaft  26 , and the low pressure turbine  24  is drivingly connected to both the booster  16  and the fan  14  with a second rotor shaft  28 , which is disposed within the first rotor shaft  26 . 
         [0015]    During operation of engine  10 , ambient air passes through the fan  14 , the booster  16 , and the compressor  18  to be pressurized in succession. Some of the ambient air is bled off for supplemental functions while the primary pressurized air stream enters the combustor  20  where it is mixed with fuel and burned to provide a high energy stream of hot combustion gases. The high-energy gas stream passes through the high-pressure turbine  22 , where it is further expanded, with energy being extracted to drive the first rotor shaft  26 . The gas stream then passes through the low-pressure turbine  24  where energy is extracted to drive the second rotor shaft  28  and, thus, the fan  14 . Spent products of combustion and unused gas pass out of the engine  10  through an exhaust duct. 
         [0016]    Referring to  FIGS. 2-4 , the compressor  18  includes an inlet guide vane stage  30  and a set of following variable vane stator stages  32 ,  34 , and  36 . The annular dimensions of each of stages  30 ,  32 ,  34 ,  36  become increasingly smaller to compress the air for use in following engine stages. Each of the stages of the compressor  18  includes a set of circumferentially arranged vanes  38  captured between a stator case  40  of the compressor  18  and a vane shroud  41 . As shown in  FIG. 3 , the shroud  41  is formed of a set of shroud sections  42 . Although a shroud is shown and described, it should be appreciated that the compressor  18  may not include a shroud and the vanes  38  may be supported between the stator case  40  and a support, for example an inner stator structure or casing, or a ring, or an engine bearing support. 
         [0017]    The vanes  38  are variably actuated by a set of variable vane actuators  44 ,  46 . The vanes  38  are coupled through the stator case  40  to the actuators  44 ,  46  by way of a vane outer trunnion  48 . The outer trunnion  48  passes through a stator case port  50  and is retained by way of an inner bushing  52  and an outer nut  54 . A lever arm  56  is captured between the bushing  52  and the outer nut  54 . The lever arm  56  is coupled to the vane actuators  44 ,  46  through linkage arms  58 . 
         [0018]    With reference to  FIGS. 3 and 4 , rotation of the vanes  38  is further enabled by the coupling of sets of the vanes  38  to respective ones of the inner vane shroud sections  42 . Each shroud section  42  includes a plurality of shroud ports  60 , each port  60  configured to accept an inner trunnion  62  of individual ones of the vanes  38 . The inner trunnion  62  includes a contact shoulder or trunnion button  64  that resides in a shroud port recess  66  having a recess shoulder. The inner trunnion  62  is initially captured in the port  60  using a shroud bushing  68  that fits in the port  60 . A shroud washer  70  forms an intermediate contact area between a bushing face of the trunnion button  64  and a trunnion face of the shroud bushing  68 . The washer  70  prevents the shroud section  42  from moving upward and significantly increases the capturing contact area between that capturing component and the inner trunnion  62 . This increases the longevity of the guide vane system and reduces maintenance obligations. 
         [0019]    The shroud sections  42  are further coupled together with a shroud seal retainer  74 . The retainer  74  extends approximately one-half of the entire inner circumference of the compressor  18 , as shown in  FIG. 3 , and effectively ties together groups of shroud sections  42  and, thereby, groups of vanes  38 . The result is a spoke effect on the interconnected cantilevered vanes  38 . The span of the retainer  74  also provides improved prevention of movement of the shroud sections  42  downward away from the inner space of the compressor  18 . Actuation and vibration effects on the shroud-to-vane interfaces are therefore reduced. 
         [0020]    Referring to  FIGS. 5 and 6 , a variable inlet guide vane arrangement according to another embodiment comprises an outer vane support  1  and an inner vane support  6 . Each guide vanes  4  includes a pinion  9  provided on a trunnion of the vane that is pivotably supported by the outer vane support  1 . A rack  3  is connected to a circumferential support member  2  and engaged with each pinion  9  of the guide vane arrangement, as shown in  FIG. 6 . The outer vane support  1  is connected to the stator case by fastener members  7  and the inner vane support  6  is covered by an inner cover member  5 . 
         [0021]    The circumferential support member  2  is connected to an actuator  8  that is configured to rotate the circumferential support member  2  to cause the rack  3  to pivot the inlet guide vanes  4  through the pinions  9 . The rack  3  may be configured to vary the opening/closing schedule of the vanes asymmetrically. The rack  3  may be non-uniform over a portion of the open-closed range. 
         [0022]    The variable vane actuators may be actuated to vary the vane opening/closing schedule asymmetrically (circumferentially) to force the onset of flow separation from the blades into a pattern that produces favorable harmonics to reduce, or possibly eliminate, the stimuli presented to the rotating blades. The vane opening/closing schedule may employ a non-linear schedule such that the asymmetry would be introduced only in the region of onset of separation. Alternatively, alternate (different) linear schedules may be used to provide a bi-linear schedule. Beyond the region of onset of separation, the asymmetry would not be used such that the vanes would be symmetrically positioned in the fully separated or fully non-separated flow regions, thus minimizing the harmonic content associated with these conditions. 
         [0023]    By varying the vane opening/closing schedule as a function of position around the circumference, the onset of separation can be controlled circumferentially. The resultant harmonic stimuli can be controlled via the separation pattern to eliminate strong harmonic content in regions where blade resonances reside, thus reducing the vibratory stresses of the blades susceptible to this stimulus. 
         [0024]    The non-linearity in the opening/closing schedule of the vanes circumferentially varies the position of each vane with respect to the other vanes in the stage to produce a pattern of separation conducive to producing low aerodynamic stimuli at frequencies near rotor blade resonance frequencies. The non-linearity in the schedule may be employed over a narrow region of the schedule where the vanes transition from fully attached flow to fully separated flow, i.e. at the region of onset of separation. At other vane positions where flow is either fully separated (vanes fully closed) or fully attached (vanes fully open), the vane opening/closing schedule is linear to provide an axisymmetric pattern to provide the lowest stimulus and most efficient operation at these more uniform conditions. 
         [0025]    Although the embodiment discussed above includes variable actuators connected to the inlet guide vanes by lever arms connected to individual inlet guide vanes that are connected to the variable actuator by linkages, it should be appreciated that other vane opening/closing mechanisms, such as gearing or elliptical cams, may be used to provide the non-linearity in the vane opening/closing schedule. 
         [0026]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.