WITH ICE MANAGEMENT

[0001] This application claims priority to United States Provisional Application No. 61/593,150, which was filed on January 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'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. Furthermore, the presence of ice on the engine can affect operation and, thus, should be managed.

SUMMARY

[0006] 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.

[0007] 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

[0008] 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.

[0009] In a further embodiment of any of the above, the adjusting step includes translating flaps to selectively block a vent in the fan nacelle. [0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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).

[0015] 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.

[0016] In a further embodiment of any of the above, the low pressure turbine has a pressure ratio that is greater than about 5. [0017] 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.

[0018] In a further embodiment of any of the above, the first position is open and the second position is closed.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] 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.

[0023] In a further embodiment of any of the above, the low pressure turbine has a pressure ratio that is greater than about 5. [0024] 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.

[0025] 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

[0026] The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0027] Figure 1 schematically illustrates an example gas turbine engine.

[0028] Figure 2 is an example schedule for varying a fan nacelle exit area based upon air speed and icing conditions.

DETAILED DESCRIPTION

[0029] Figure 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.

[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. "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) ^Λ 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 PI, P2 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 P2, 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 PI, 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 corrected low fan tip speed.

[0038] 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 Figure 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. [0039] One example schedule 80 for a target variable area fan nozzle position, corresponding to fan nozzle exit area, based upon airspeed is illustrated in Figure 2. As shown in the example in Figure 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.

[0040] 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 PI in Figure 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.

[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.