Abstract:
An example variable vane scheduling method includes adjusting variable vanes from a position based on a first schedule to a position based on a different, second schedule in response to a control feature. An example method of controlling flow through a compressor of a turbomachine includes moving variable vanes to positions that allow more flow into the compressor in response to bleed air being communicated away from the compressor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/706418, which was filed on 27 Sep. 2012 and is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Turbomachines, such as gas turbine engines, typically include a fan section, a compression section, a combustion section, and a turbine section. Turbomachines may employ a geared architecture connecting portions of the compression section to the fan section. 
         [0003]    Variable vanes are widely used in commercial and military gas turbine engines, especially within compression sections. Variable vane position is typically scheduled as a function of corrected engine parameters and additional factors, such as throttle movements, foreign object detection, and stall detection. Variable vane positioning permits optimal airfoil incidence to protect compressor stability. 
       SUMMARY 
       [0004]    A method of variable vane scheduling according to an exemplary aspect of the present disclosure includes, among other things, adjusting variable vanes from a position based on a first schedule to a position based on a different, second schedule in response to a control feature. 
         [0005]    In a further non-limiting embodiment of the foregoing method of variable vane scheduling, the control feature comprises an amount of bleed air. 
         [0006]    In a further non-limiting embodiment of either of the foregoing methods of variable vane scheduling, the first schedule may include positions that permit a first amount of flow into a compressor, and the second schedule may include positions that permit a second amount of flow into the compressor. The first amount is less than the second amount. 
         [0007]    In a further non-limiting embodiment of any of the foregoing methods of variable vane scheduling, the variable vanes may be adjusted according to the first schedule when the amount of bleed air is relatively low, and the variable vanes may be adjusted according to the second schedule when the amount of bleed air is relatively high. 
         [0008]    In a further non-limiting embodiment of any of the foregoing methods of variable vane scheduling, the variable vanes may be adjusted based on the first schedule when the amount of bleed air is zero. 
         [0009]    In a further non-limiting embodiment of any of the foregoing methods of variable vane scheduling, the variable vanes may control flow through a compressor of a turbomachine, and the first and the second schedules determine the position based on a variable that includes at least a rotational speed of a rotor of the compressor and a temperature of the compressor. 
         [0010]    In a further non-limiting embodiment of any of the foregoing methods of variable vane scheduling, the variable may include the rotational speed divided by the temperature. 
         [0011]    In a further non-limiting embodiment of any of the foregoing methods of variable vane scheduling, the temperature may be a compressor inlet temperature. 
         [0012]    In a further non-limiting embodiment of any of the foregoing methods of variable vane scheduling, the method may use a position of a bleed valve to determine the amount of bleed air. 
         [0013]    A turbomachine controller assembly according to an exemplary aspect of the present disclosure includes, among other things, a controller configured to adjust an array of variable vanes within a compressor, wherein the controller adjusts the array according to a first schedule when a first amount of bleed air is communicated from the compressor, and adjusts the array according to a second schedule when a different, second amount of bleed air is communicated from the compressor. 
         [0014]    In a further non-limiting embodiment of the foregoing turbomachine controller assembly, the first schedule may include positions that permit less flow through the compressor than the positions of the second schedule. 
         [0015]    In a further non-limiting embodiment of either of the foregoing turbomachine controller assemblies, the second amount of bleed air may comprise no bleed air communicated from the compressor. 
         [0016]    In a further non-limiting embodiment of any of the foregoing turbomachine controller assemblies, the controller may monitor a bleed valve position to determine whether the first amount or the second amount of bleed air is communicated from the compressor. 
         [0017]    In a further non-limiting embodiment of any of the foregoing turbomachine controller assemblies, the first and the second schedules may be determined based at least on a compressor rotor speed and an inlet temperature. 
         [0018]    A method of controlling flow through a compressor of a turbomachine according to another exemplary aspect of the present disclosure includes, among other things, moving variable vanes to positions that allow more flow into the compressor in response to bleed air being communicated away from the compressor. 
         [0019]    In a further non-limiting embodiment of the foregoing method of controlling flow through a compressor of a turbomachine, the variable vanes may be moved according to at least a first schedule or a second schedule. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0020]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0021]      FIG. 1  shows a section view of an example turbomachine. 
           [0022]      FIG. 2  shows example schedules for variable vanes of the turbomachine of  FIG. 1 . 
           [0023]      FIG. 3  shows a highly schematic view of flow entering a compression section of the turbomachine of  FIG. 1  when a bleed valve is in a position permitting less bleed flow. 
           [0024]      FIG. 4  shows a highly schematic view of flow entering a compression section of the turbomachine of  FIG. 1  when a bleed valve is in a position permitting more bleed flow. 
           [0025]      FIG. 5  shows example bounded schedules for variable vanes of the turbomachine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  schematically illustrates an example turbomachine, which is a gas turbine engine  20  in this example. The gas turbine engine  20  is a two-spool turbofan gas turbine engine that generally includes a fan section  22 , a compression section  24 , a combustion section  26 , and a turbine section  28 . 
         [0027]    Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans. That is, the teachings may be applied to other types of turbomachines and turbine engines including three-spool architectures. Further, the concepts described herein could be used in environments other than a turbomachine environment and in applications other than aerospace applications. 
         [0028]    In the example engine  20 , flow moves from the fan section  22  to a bypass flowpath. Flow from the bypass flowpath generates forward thrust. The compression section  24  drives air along a core flowpath. Compressed air from the compression section  24  communicates through the combustion section  26 . The products of combustion expand through the turbine section  28 . 
         [0029]    The example engine  20  generally includes a low-speed spool  30  and a high-speed spool  32  mounted for rotation about an engine central axis A. The low-speed spool  30  and the high-speed spool  32  are rotatably supported by several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively, or additionally, be provided. 
         [0030]    The low-speed spool  30  generally includes a shaft  40  that interconnects a fan  42 , a low-pressure compressor  44 , and a low-pressure turbine  46 . The shaft  40  is connected to the fan  42  through a geared architecture  48  to drive the fan  42  at a lower speed than the low-speed spool  30 . 
         [0031]    The high-speed spool  32  includes a shaft  50  that interconnects a high-pressure compressor  52  and high-pressure turbine  54 . 
         [0032]    The shaft  40  and the shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with the longitudinal axes of the shaft  40  and the shaft  50 . 
         [0033]    The combustion section  26  includes a circumferentially distributed array of combustors  56  generally arranged axially between the high-pressure compressor  52  and the high-pressure turbine  54 . 
         [0034]    In some non-limiting examples, the engine  20  is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6 to 1). 
         [0035]    The geared architecture  48  of the example engine  20  includes an epicyclic gear train, such as a planetary gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about 2.3 (2.3 to 1). 
         [0036]    The low-pressure turbine  46  pressure ratio is pressure measured prior to inlet of low-pressure turbine  46  as related to the pressure at the outlet of the low-pressure turbine  46  prior to an exhaust nozzle of the engine  20 . In one non-limiting embodiment, the bypass ratio of the engine  20  is greater than about ten (10 to 1), the fan diameter is significantly larger than that of the low-pressure compressor  44 , and the low-pressure turbine  46  has a pressure ratio that is greater than about 5 (5 to 1). The geared architecture  48  of this embodiment is an epicyclic gear train with a gear reduction ratio of greater than about 2.5 (2.5 to 1). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans. 
         [0037]    In this embodiment of the example engine  20 , a significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. This flight condition, with the engine  20  at its best fuel consumption, is also known as “Bucket Cruise” Thrust Specific Fuel Consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust. 
         [0038]    Fan Pressure Ratio is the pressure ratio across a blade of the fan section  22  without the use of a Fan Exit Guide Vane system. The low Fan Pressure Ratio according to one non-limiting embodiment of the example engine  20  is less than 1.45 (1.45 to 1). 
         [0039]    “Low Corrected Fan Tip Speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram° R)/(518.7 ° R)]̂0.5. The Temperature represents the ambient temperature in degrees Rankine. The Low Corrected Fan Tip Speed according to one non-limiting embodiment of the example engine  20  is less than about 1150 fps (351 m/s). 
         [0040]    The engine  10  includes arrays of variable vanes  58  extending radially from the axis A. The variable vanes  58  are positioned, in this example, near the inlet to the high-pressure compressor  52 . The low-pressure compressor  44  may include variable vanes in some examples. 
         [0041]    The variable vanes  58  are adjusted between positions that permit more flow and positions that permit less flow into the high-pressure compressor  52 . The variable vanes  58  are typically adjusted by rotating the variable vanes  58  about radially extending axes, as is known. 
         [0042]    Referring the  FIG. 2  with continuing reference to  FIG. 1 , the example controller  60  adjusts the positions of the variable vanes  58  according to a first schedule  72  or a second schedule  74 . The first schedule  72  specifies a first position for the variable vanes  58  for a given variable from the engine  20 . The second schedule  74  specifies a different, second position for the variable vanes  58  for the variable from the engine  20 . At a given variable, the first position of the first schedule  72  permits less flow through the variable vanes  58  to the high-pressure compressor  52  than the second position of the second schedule  74 . 
         [0043]    The variable is typically the rotational speed of the high-speed spool  32  divided by a temperature at an inlet to the high-pressure compressor  52 . Other variables are possible. The first positions in the first schedule  72  and the second positions in the second schedule  74  are functions of the variables in this example. 
         [0044]    Referring now to  FIGS. 3 and 4 , the controller  60  moves the variable vanes  28  according to the first schedule  72  depending on a control feature, such as when a bleed valve  80  of the high-pressure compressor  52  is closed and not communicating bleed air from the high-pressure compressor  52 . The controller  60  moves the variable vanes  28  according to the second schedule  74  when the bleed valve  80  of the high-pressure compressor  52  is open and communicating bleed air from the high-pressure compressor  52 . 
         [0045]    In another example, the controller  60  moves the variable vanes  28  according to the first schedule  72  when horsepower extraction of an aircraft associated with the engine  20  is above a set value, and moves the variable vanes  28  according to the second schedule  72  when horsepower extraction of the aircraft is below the set value. 
         [0046]    In some examples, the set value represents different levels of horsepower, such as no horsepower, normal horsepower, and maximum horsepower. The specific value of the horsepower (hp) may vary significantly based on the type of engine  20  and aircraft. For example, one engine may use 0 hp, 100 hp, and 200 hp. In such an example, 0 hp may correspond to a failure case when a generator of the engine  20  is malfunctioning and is turned off, 100 hp may be ‘normal’ load on the engine  20  during the entire mission (having no flight condition dependence), and 200 hp may correspond to a maximum load during icing conditions with multiple flight surfaces moving and gear deploying. Another engine may use 0 hp, 75 hp, and 150 hp as the different levels of horsepower. 
         [0047]    This mode of operation, which uses horsepower extraction rather than bleed air as the control feature, may be especially relevant if the engine  20  has all electric offtakes. Example of such engines include engines that rely on mechanical energy extraction (horsepower) to provide breathing air and run aircraft control surfaces. Other engines, by contrast, extract bleed air from the compressor for the cabin and use hydraulic pumps attached to the engine to power the control surfaces. Both bleed air and horsepower extraction influence stability of the high-pressure compressor  52 . Other examples use control features other than bleed air or horsepower extraction. 
         [0048]    In this example, opening the bleed valve  80  permits bleed air to move from the high-pressure compressor  52 . The bleed valve  80  may be a single valve, or several valves and passages that selectively permit movement of bleed air from the high-pressure compressor  52 . The valves and passages may be at several stages of the high-pressure compressor  52 . 
         [0049]    Bleed air is moved from the high-pressure compressor  52  to, for example, cool various components of the engine  20 , such a vanes and blades. Moving bleed air from the high-pressure compressor  52  means that less air passes from the high-pressure compressor  52  to the combustors  56 , and to the turbine section  28 . Less air moving to the turbine section  28  may reduce the useful life of components within the turbine section  28 , especially in high-bypass ratio engines. 
         [0050]    The example controller  60  compensates for the bleed air moving from the high-pressure compressor  52  by adjusting the variable vanes  58  according to the second schedule  74  when the bleed air is moving from the high-pressure compressor  52 . The second schedule  74 , at a given speed and temperature, permits more flow into the high-pressure compressor  52  than the first schedule  72 . 
         [0051]    The controller  60  may monitor a position of the bleed valve  80  to determine whether bleed air is moving from the high-pressure compressor  52 . The controller  60  may monitor whether bleed air is moving from the high-pressure compressor  52  in some other way, such as via a sensor that detects bleed air. 
         [0052]    Various vane schedules are created to optimize performance of the engine  10 . The first and second schedules may include a range of positions, as shown in the schedules  72   a  and  74   a  of  FIG. 5 . The upper boundaries of the schedules  72   a  and  74   a  may represent the stability limits associated with the variable vanes  58 . 
         [0053]    Although described as two distinct vane schedules, more than two vane schedules may be used. For example, the variable vanes may be adjusted according to a first schedule when a bleed valve is closed, a second schedule when the bleed valve is partially open, and a third schedule when the bleed valve is fully open. 
         [0054]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.