Abstract:
A method of managing a gas turbine engine includes the steps of detecting an airspeed and detecting a fan speed. A parameter relationship is referenced related to a desired variable area fan nozzle position based upon at least airspeed and fan speed. The detected airspeed and detected fan speed is compared to the parameter relationship to determine a target variable area fan nozzle position. An actual variable area fan nozzle position is adjusted in response to the determination of the target area fan nozzle position and at least one threshold.

Description:
[0001]    This application is a continuation of U.S. Ser. No. 13/365,455, which was filed on Feb. 03, 2012 which claims priority to U.S. Provisional Application No. 61/592,984, which was filed on Jan. 31, 2012. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to managing gas turbine engine fan operability and operating characteristics using a variable area fan nozzle. 
         [0003]    One typical gas turbine engine includes low and high speed spools housed within a core nacelle. The low speed spool supports a low pressure compressor and turbine, and the high speed spool supports a high pressure compressor and turbine. A fan is coupled to the low speed spool. A fan nacelle surrounds the fan and core nacelle to provide a bypass flow path having a nozzle. Typically, the nozzle is a fixed structure providing a fixed nozzle exit area. 
         [0004]    The fan&#39;s operating line must be controlled to avoid undesired conditions such as fan flutter, surge or stall. The fan operating line can be manipulated during engine operation to ensure that the fan operability margin is sufficient. The fan operating line is defined, for example, by characteristics including low spool speed, bypass airflow and turbofan pressure ratio. Manipulating any one of these characteristics can change the fan operating line to meet the desired fan operability margin to avoid undesired conditions. 
         [0005]    The engine is designed to meet the fan operability line and optimize the overall engine performance throughout the flight envelope. As a result, the engine design is compromised to accommodate various engine operating conditions that may occur during the flight envelope. For example, fuel consumption for some engine operating conditions may be less than desired in order to maintain the fan operating line with an adequate margin for all engine operating conditions. For example, fan operating characteristics are compromised, to varying degrees, from high Mach number flight conditions to ground idle conditions for fixed nozzle area turbofan engines. This creates design challenges and/or performance penalties to manage the operability requirements. 
       SUMMARY 
       [0006]    In one exemplary embodiment, a method of managing a gas turbine engine includes the steps of detecting an airspeed and detecting a fan speed. A parameter relationship is referenced related to a desired variable area fan nozzle position based upon at least airspeed and fan speed. The detected airspeed and detected fan speed is compared to the parameter relationship to determine a target variable area fan nozzle position. An actual variable area fan nozzle position is adjusted in response to the determination of the target area fan nozzle position and at least one threshold. 
         [0007]    In a further embodiment of any of the above, the fan speed detecting step includes detecting a low speed spool rotational speed and correcting the fan speed based upon an ambient temperature. 
         [0008]    In a further embodiment of any of the above, the fan speed detecting step includes calculating the fan speed based upon a gear reduction ratio. 
         [0009]    In a further embodiment of any of the above, the referencing and comparing steps include providing a target variable area fan nozzle position for a range of air speeds based upon the fan speed. 
         [0010]    In a further embodiment of any of the above, the air speed range is 0.35-0.55 Mach. The data table includes first and second thresholds corresponding to lower and upper fan speed limits. The target variable area fan nozzle position is selected based upon the first and second thresholds. 
         [0011]    In a further embodiment of any of the above, the upper fan speed limit is 60% of an aerodynamic design speed of the fan, and the lower fan speed limit is 75% of the aerodynamic design speed of the fan. 
         [0012]    In a further embodiment of any of the above, the upper fan speed limit is 65% of the aerodynamic design speed of the fan. 
         [0013]    In a further embodiment of any of the above, the lower fan speed limit is 75% of the aerodynamic design speed of the fan. 
         [0014]    In a further embodiment of any of the above, the adjusting step includes adjusting the target variable fan nozzle position to provide an exit area of a fan nacelle. 
         [0015]    In a further embodiment of any of the above, the adjusting step includes translating the flaps to selectively block a vent in the fan nacelle. 
         [0016]    In a further embodiment of any of the above, the gas turbine engine includes a fan arranged in a fan nacelle having a flap configured to be movable between first and second positions. An actuator is operatively coupled to the flap. A compressor section is fluidly connected to the fan, and the compressor includes a high pressure compressor and a low pressure compressor. A combustor is fluidly connected to the compressor section, and a turbine section is fluidly connected to the combustor. The turbine section includes a high pressure turbine coupled to the high pressure compressor via a shaft, and a low pressure turbine. 
         [0017]    In a further embodiment of any of the above, the gas turbine engine is a geared aircraft engine having a bypass ratio of greater than about six (6). 
         [0018]    In a further embodiment of any of the above, the gas turbine engine includes a low Fan Pressure Ratio of less than about 1.45. 
         [0019]    In a further embodiment of any of the above, the low pressure turbine has a pressure ratio that is greater than about 5. 
         [0020]    In another exemplary embodiment, a gas turbine engine includes a fan nacelle that includes a flap that is configured to be movable between first and second positions. An actuator is operatively coupled to the flap. A controller is configured to reference a parameter relationship that relates to a desired variable area fan nozzle position based upon at least airspeed and fan speed. The controller is configured to compare a detected airspeed and a detected fan speed to the parameter relationship to determine a target variable area fan nozzle position. The controller is configured to provide a command to the actuator to adjust the flap from a first position to the second position in response to the determination of the target variable fan nozzle position and at least one threshold. 
         [0021]    In a further embodiment of any of the above, a fan is arranged in the fan nacelle. A compressor section is fluidly connected to the fan, and the compressor includes a high pressure compressor and a low pressure compressor. A combustor is fluidly connected to the compressor section, and a turbine section is fluidly connected to the combustor. The turbine section includes a high pressure turbine coupled to the high pressure compressor via a shaft, and a low pressure turbine. 
         [0022]    In a further embodiment of any of the above, the gas turbine engine is a geared aircraft engine having a bypass ratio of greater than about six (6). 
         [0023]    In a further embodiment of any of the above, the gas turbine engine includes a low Fan Pressure Ratio of less than about 1.45. 
         [0024]    In a further embodiment of any of the above, the low pressure turbine has a pressure ratio that is greater than about 5. 
         [0025]    In a further embodiment of any of the above, the controller is configured to provide a target variable area fan nozzle position for a range of air speeds based upon the fan speed. The air speed range is 0.35-0.55 Mach. The data table includes first and second thresholds that correspond to lower and upper fan speed limits. The target variable area fan nozzle position is selected based upon the first and second thresholds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0027]      FIG. 1  schematically illustrates an example gas turbine engine. 
           [0028]      FIG. 2  is an example schedule for varying a fan nacelle exit area based upon air speed and fan speed. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flowpath while the compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a 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 as the teachings may be applied to other types of turbine engines including three-spool architectures. 
         [0030]    The engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
         [0031]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner 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 . The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  supports one or more bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A, which is collinear with their longitudinal axes. 
         [0032]    The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core airflow path. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
         [0033]    The engine  20  in one example a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and, for example, greater than about 2.5:1 and the low pressure turbine  46  has a pressure ratio that is greater than about 5. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), 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 5:1. 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. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
         [0034]    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. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm per hour of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, regardless of the presence of a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tambient deg R)/518.7)̂0.5]. The “Low corrected fan tip speed,” as disclosed herein according to one non-limiting embodiment, is less than about 1150 ft/second. 
         [0035]    A core nacelle  61  surrounds the engine static structure  36 . A fan nacelle  58  surrounds the core nacelle  61  to provide the bypass flow path. In the example engine  20 , a nozzle exit area  60  is effectively variable to alter the bypass flow B and achieve a desired target operability line. In one example, the fan nacelle  58  includes moveable flaps  62  near the bypass flowpath exit, which may be provided by arcuate segments that are generally linearly translatable parallel to the axis A in response to inputs by one or more actuators  66 . 
         [0036]    The flaps  62  are moveable between first and second positions P 1 , P 2  and positions in between. The flaps  62  selectively regulate by blocking, a size of an annular vent  64  provided between a trailing end  63  of the nacelle body and a leading edge  65  of the flaps  62 . The vent  64  is fully open in the second position P 2 , in which a vent flow V from the bypass flowpath is permitted to exit through the vent  64 . An open vent  64  increases the bypass flow B and effectively increases the nozzle exit area  60 . With the flaps  62  in the first position P 1 , flow from the bypass flowpath is not permitted to pass through the vent  64 , which is blocked by the flaps  62 . 
         [0037]    A controller  68  is in communication with a low speed spool sensor  70 , which detects a rotational speed of the low speed spool  30 . A temperature sensor  72  detects the ambient temperature. Air speed  74  is provided to the controller  68 , as is the ambient temperature. In the example, the controller  68  may store various parameters  76  relating to the engine  20 , such as a gear reduction ratio of the geared architecture  48 , outer diameter of the fan  22  and other information useful in calculating a low corrected fan tip speed. 
         [0038]    A parameter relationship  78 , which may be one or more data tables and/or equations and/or input-output data chart etc., for example, may be stored in the controller  68 . The parameter relationship  78  includes information relating to air speed, fan speed and a desired variable area fan nozzle position, which provide a schedule illustrated in  FIG. 2 . One example of the parameter relationship  78  is a bivarient lookup table. In operation, the turbofan engine operating line is managed by detecting the air speed and the fan speed, for example, by determining the low speed spool rotational speed. In should be understood, however, that the fan speed may be inferred from the low speed spool rotational speed rather than calculated. That is, only the low speed spool rotational speed could be monitored and compared to a reference low speed spool rotational speed in the parameter relationship  78 , rather than a fan speed. The controller  68  references the parameter relationship  78 , which includes a desired variable area fan nozzle position relative to the air speed and fan speed. The detected air speed and fan speed, which may be detected in any order, are compared to the data table to provide a target variable area fan nozzle position. The controller  68  commands the actuators  66  to adjust the flaps  62  from an actual variable area fan nozzle position, or the current flap position, to the target variable area fan nozzle position. 
         [0039]    One example schedule is illustrated in  FIG. 2 . Multiple data curves are provided, which correspond to different fan speeds. The curves, which are linear in one example, provide first and second thresholds  80 ,  82  that respectively relate to upper and lower limits for the target variable area fan nozzle position as it relates to a range of air speeds. As shown in the example in  FIG. 2 , air speeds of between about 0.35 Mach and 0.55 Mach, and in one example, between about 0.38 Mach and 0.50 Mach, provide a region in which the nozzle exit area is adjusted based upon fan speed. Below 0.35 Mach and above 0.55 Mach, the nozzle exit area is respectively at its maximum and minimum and the fan speed need not be used to determine the target variable area fan nozzle position. For air speeds between 0.35 Mach and 0.55 Mach, the fan speed is used to determine a target variable area fan nozzle position. 
         [0040]    In  FIG. 2 , the percent speed value represents the engine operating fan speed relative to the fan aerodynamic design speed (FEDS). In one example, the upper limit is defined at 60% of the FEDS, and the lower limit is defined at 75% of the FEDS. In another example, the upper and lower limits are defined respectively 65% and 70% of a particular fan speed. In the example of 0.45 Mach shown in  FIG. 2 , if the detected fan speed is above 70% of a particular fan speed, the target variable area fan nozzle position will be 40% of the maximum open position (point A). If the detected fan speed is less than 65% of a particular fan speed, the target variable area fan nozzle position will be at the maximum open position (point B in  FIG. 2 , second position P 2  in  FIG. 1 ). For fan speeds between the lower and upper thresholds  80 ,  82 , the target variable area fan nozzle positions are averaged, for example. So, for a fan speed of 67% of a particular fan speed, the target variable area fan nozzle position is 75% of the maximum open position (point C). In this manner, the fan speed, or low speed spool rotational speed, is used to determine the target variable area fan nozzle position at a particular range of air speed. 
         [0041]    The controller  68  can include a processor, memory, and one or more input and/or output (I/O) device interface(s) that are communicatively coupled via a local interface. The local interface can include, for example but not limited to, one or more buses and/or other wired or wireless connections. The local interface may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. 
         [0042]    The controller  68  may be a hardware device for executing software, particularly software stored in memory. The controller  68  can be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computing device, a semiconductor based microprocessor (in the form of a microchip or chip set) or generally any device for executing software instructions. 
         [0043]    The memory can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, VRAM, etc.)) and/or nonvolatile memory elements (e.g., ROM, hard drive, tape, CD-ROM, etc.). Moreover, the memory may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory can also have a distributed architecture, where various components are situated remotely from one another, but can be accessed by the processor. 
         [0044]    The software in the memory may include one or more separate programs, each of which includes an ordered listing of executable instructions for implementing logical functions. A system component embodied as software may also be construed as a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When constructed as a source program, the program is translated via a compiler, assembler, interpreter, or the like, which may or may not be included within the memory. 
         [0045]    The Input/Output devices that may be coupled to system I/O Interface(s) may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, camera, proximity device, etc. Further, the Input/Output devices may also include output devices, for example but not limited to, a printer, display, etc. Finally, the Input/Output devices may further include devices that communicate both as inputs and outputs, for instance but not limited to, a modulator/demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. 
         [0046]    The controller  68  can be configured to execute software stored within the memory, to communicate data to and from the memory, and to generally control operations of the computing device pursuant to the software. Software in memory, in whole or in part, is read by the processor, perhaps buffered within the processor, and then executed. 
         [0047]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.