Abstract:
A method of managing a gas turbine engine variable area fan nozzle includes the steps of evaluating an icing condition to determine the likelihood of ice presence. A variable area fan nozzle position is altered if ice is likely present or actually present. The gas turbine engine includes a fan nacelle including a flap configured to be moveable between first and second positions. An actuator is operatively coupled to the flap. A controller is configured to evaluate an icing condition to determine the likelihood of ice presence. The controller is configured to alter a variable area fan nozzle position schedule if ice is likely present by providing a command to the actuator to adjust the flap from the first position to the second position.

Description:
This application claims priority to U.S. Provisional Application No. 61/593,150, which was filed on Jan. 31, 2012. 
    
    
     BACKGROUND 
     This disclosure relates to managing gas turbine engine fan operability and operating characteristics using a variable area fan nozzle. 
     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. 
     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. 
     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. Furthermore, the presence of ice on the engine can affect operation and, thus, should be managed. 
     SUMMARY 
     A method of managing a gas turbine engine variable area fan nozzle includes the step of evaluating an icing condition to determine the likelihood of ice presence. A variable area fan nozzle position is altered if ice is likely present or actually present. 
     In a further embodiment of any of the above, the evaluating step includes using an algorithm that relies upon one or more icing condition inputs from at least one of a temperature sensor, air speed and a humidity sensor 
     In a further embodiment of any of the above, the altering step includes adjusting a fan nacelle exit area in response to an altered variable area fan nozzle position schedule. 
     In a further embodiment of any of the above, the adjusting step includes translating flaps to selectively block a vent in the fan nacelle. 
     In a further embodiment of any of the above, the variable area fan nozzle position schedule corresponds to the flaps being at least partially open at air speeds below 0.55 Mach. The altering step includes closing the flaps below 0.55 Mach. 
     In a further embodiment of any of the above, the variable area fan nozzle position schedule corresponds to the flaps at least partially open at air speeds below 0.55 Mach, and the altering step includes closing the flaps below 0.55 Mach. 
     In a further embodiment of any of the above, the flaps are fully open below 0.38 Mach in an unaltered variable area fan nozzle position schedule. 
     In a further embodiment of any of the above, the gas turbine engine includes a fan is arranged in a fan nacelle including a flap configured to be movable between first and second positions. An actuator is operative 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. 
     In a further embodiment of any of the above, the gas turbine engine is a high bypass geared aircraft engine having a bypass ratio of greater than about six (6). 
     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. 
     In a further embodiment of any of the above, the low pressure turbine has a pressure ratio that is greater than about 5. 
     The gas turbine engine includes a fan nacelle having a flap configured to be moveable between first and second positions. An actuator is operatively coupled to the flap. A controller is configured to evaluate an icing condition to determine the likelihood of ice presence. The controller is configured to alter a variable area fan nozzle position schedule if ice is likely present or actually present by providing a command to the actuator to adjust the flap from the first position to the second position. 
     In a further embodiment of any of the above, the first position is open and the second position is closed. 
     In a further embodiment of any of the above, a geared architecture is coupled between a low speed spool and a fan. The fan is arranged within the fan nacelle. 
     In a further embodiment of any of the above, 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. 
     In a further embodiment of any of the above, the gas turbine engine is a high bypass geared aircraft engine having a bypass ratio of greater than about six (6). 
     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. 
     In a further embodiment of any of the above, the low pressure turbine has a pressure ratio that is greater than about 5. 
     In a further embodiment of any of the above, the variable area fan nozzle position schedule corresponds to the flaps at least partially open at air speeds below 0.55 Mach, and the command includes closing the flaps below 0.55 Mach. 
     In a further embodiment of any of the above, the flaps are fully open below 0.38 Mach in an unaltered variable area fan nozzle position schedule. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  schematically illustrates an example gas turbine engine. 
         FIG. 2  is an example schedule for varying a fan nacelle exit area based upon air speed and icing conditions. 
     
    
    
     DETAILED DESCRIPTION 
       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 a three-spool architecture, an augmentor section, or different engine section arrangements, 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. 
     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. 
     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. 
     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. 
     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. 
     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. “Fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The 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. 
     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 . 
     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 . 
     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 corrected low fan tip speed. 
     A parameter relationship  78 , such as one or more data tables (such as a bivariant look-up table) and/or equations, 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 . In operation, the turbofan engine operating line is managed by detecting the air speed and other parameters, such as 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. In one example, the detected air speed and fan speed 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. 
     One example schedule  80  for a target variable area fan nozzle position, corresponding to fan nozzle exit area, based upon airspeed is illustrated in  FIG. 2 . As shown in the example in  FIG. 2 , the flaps  62  are at least partially open at air speeds below 0.55 Mach, and in another example, below 0.50 Mach. In one example, the flaps  62  are fully opened below 0.38 Mach in an unaltered variable area fan nozzle position schedule. 
     An icing condition input  84  communicates with and is used by the controller  68 . The icing condition input  84  is used to predict the presence of ice in the area of the vent  62  using the parameter relationship  78 , for example, which could inhibit desired operation of the flaps  62  during the flight envelope. In one example, an algorithm determines the likelihood of the presence of ice using data from a temperature sensor, air speed, humidity sensor and/or other devices or information determines the likelihood of ice presence near or at the vent  62 . If an ice condition is detected, either actual or predicted ice presence, below 0.55 Mach, the normal schedule  80  is altered to provide an icing schedule  82 , and the flaps  62  are moved to or maintained in a closed position (first position P 1  in  FIG. 1 ), for the example, where the fan speed is below 65% of the fan aerodynamic design speed. In one example, the schedule  80  is altered by commanding the flaps  62  to the closed position. In another example where the fan speed is above 70% of the fan aerodynamic design speed, the variable area fan nozzle position follows schedule  80  as a function of airspeed. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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.