Abstract:
An example turbofan engine starting system includes a core nacelle housing a compressor and a turbine. The core nacelle is disposed within a fan nacelle. The fan nacelle includes a turbofan. A bypass flow path downstream from the turbofan is arranged between the two nacelles. A controller is programmed to manipulate the nozzle exit area to facilitate startup of the engine. In one example, manipulates the nozzle exit area using nozzles, in response to an engine shutdown condition. The nozzles open and close to adjust the nozzle exit area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/441756 filed on 18 Mar. 2009, which is a National Stage Entry of PCT Application No. PCT/US06/39943 filed on 12 Oct. 2006. Both of these applications are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to starting gas turbine engines, and, more particularly, to facilitating gas turbofan engine restarts by effectively altering the nozzle exit area. 
         [0003]    Gas turbine engines are widely known and used for power generation and vehicle (e.g., aircraft) propulsion. During in-flight propulsion of a multi-engine aircraft, certain problems may occur with one or more engines causing the engine to shut down. For example, inclement weather, non-optimum trimming of engine idle, fuel nozzle coking, fuel contamination, loss of electric power, fuel mismanagement, pilot error, or the like may, under certain conditions, warrant voluntary or automatic shut down of an engine. Although the remaining engines can typically fly the aircraft, it is ordinarily desired to restart the shut down engine while the aircraft is still in-flight. 
         [0004]    An engine restart envelope includes combinations of aircraft altitude and airspeed that provide a suitable air supply to the engine sufficient for restarting. When traveling outside of the engine restart envelope, the air supply to the engine may not contain sufficient air to support combustion during ignition. In some instances, starter-assistance may be used to increase the rotational speed of a fan section of the engine, which increases altitude and airspeed combinations suitable for restarting the engine. Increasing the rotational speed of the fan section draws additional airflow into the engine and, in so doing, augments the supply of air supporting combustion. 
         [0005]    Disadvantageously, at certain combinations of altitude and airspeed, increasing the rotational speed of the fan section is not alone sufficient to generate adequate airflow to support combustion. As a result, aircraft experiencing in-flight shutdown may have to rapidly adjust altitude and/or airspeed to move within the engine restart envelope or starter-assisted engine restart envelope. As an example, if an engine requires restart in aircraft traveling at an altitude unsuitable for engine restarts, the aircraft may rapidly decrease elevation to move to an altitude suitable for restarting the turbofan engine. Alternatively, the aircraft may be forced to continue flying, without propulsion from the shutdown engine. 
       SUMMARY 
       [0006]    A turbofan engine restarting system, according to an exemplary aspect of the present disclosure includes, among other things, a core nacelle housing a compressor and a turbine, a fan nacelle housing a fan section that is arranged upstream from the core nacelle, a bypass flow path downstream from the fan section and arranged between the core and fan nacelles, the bypass flow path including an effective nozzle exit area that defines an axis, a controller programmed to selectively increase and decrease the effective nozzle exit area to facilitate restart of the engine during flight in air. The effective nozzle area is increased when the nozzle effective area is not a maximum effective nozzle area, and a starter for increasing a rotational speed of the fan section, and a control device arranged to receive a command from the controller in response to an engine condition. The control device changing the effective nozzle exit area provided between the core and fan nacelles in response to the command 
         [0007]    In another example of the foregoing system, a plurality of flaps are arranged about the axis, the controller initiates movement of at least some of the flaps radially away from the axis and from a position suitable for aircraft cruising operations to increase the effective nozzle exit area, and initiates movement of at least some of the flaps radially toward the axis to decrease the effective nozzle exit area. 
         [0008]    In another example of any of the foregoing systems, the increase occurs when the effective nozzle exit area of the bypass flow path is not a maximum effective nozzle exit area of the bypass flowpath. 
         [0009]    In another example of any of the foregoing systems, the control device increases or decreases the effective nozzle exit area in response to the command 
         [0010]    In another example of any of the foregoing systems, the control device increases a mass flow rate of air through the bypass flow path. 
         [0011]    In another example of any of the foregoing systems, an increased mass flow rate of air through the bypass flow path increases a windmilling speed of the fan section. 
         [0012]    In another example of any of the foregoing systems, the system includes a driver for initiation by an aircraft operator and in communication with the controller, the controller sending the command in response to actuation of the driver. 
         [0013]    In another example of any of the foregoing systems, the engine condition includes a rotational speed of a portion of the engine. 
         [0014]    In another example of any of the foregoing systems, the system includes at least one nozzle flap disposed on the fan nacelle operative to control the effective nozzle exit area. 
         [0015]    A method of restarting a turbofan engine according to another exemplary aspect of the present disclosure includes, among other things, a) detecting a shutdown of a turbofan engine during flight in air, selectively increasing and decreasing an effective nozzle exit area from a bypass flow path within the engine in response to the shutdown during a flight in air to establish a desired condition for a startup of the engine during the flight in air, the increasing and decreasing achieved by changing a physical area of an exit nozzle, the exit nozzle provided by a turbofan nacelle surrounding a fan section and a core nacelle, and c) increasing the rotational speed of a fan section of the engine using a starter. 
         [0016]    In another example of the foregoing method, a controller commands a control device to change the effective nozzle exit area. 
         [0017]    In another example of any of the foregoing methods, the controller commands the control device based on a rotational speed of a rotor. 
         [0018]    In another example of any of the foregoing methods, the controller commands the control device based on at least one of an airflow rate or an air pressure within the engine. 
         [0019]    In another example of any of the foregoing methods, the step (b) includes increasing the effective nozzle exit area to increase a rotational speed of a rotor within the engine. 
         [0020]    In another example of any of the foregoing methods, the step (b) includes decreasing the effective nozzle exit area to increase a mass flow rate of air through a portion of the engine. 
         [0021]    In another example of any of the foregoing methods, the step (b) includes increasing the effective nozzle exit area and then decreasing the effective nozzle exit area to the increase mass flow rate of air through a portion of the engine. 
         [0022]    In another example of any of the foregoing methods, the method includes selectively increasing combinations of altitude and airspeed suitable for restarting the turbofan engine. 
         [0023]    In another example of any of the foregoing methods, the increasing occurs when the effective nozzle exit area of the bypass flow path is not a maximum effective nozzle exit area of the bypass flowpath. 
         [0024]    These and other features of the present disclosure can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
           [0026]      FIG. 1  illustrates selected portions of an example gas turbine engine system. 
           [0027]      FIG. 2  illustrates a variable air nozzle and coolant passage within the gas turbine engine system shown in  FIG. 1 . 
           [0028]      FIG. 3  illustrates an example turbofan engine restart envelope without assistance from a variable area nozzle. 
           [0029]      FIG. 4  illustrates an example turbofan engine restart envelope with assistance from a variable area nozzle. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    A geared turbofan engine  10  is shown in  FIG. 1 . The engine  10  includes a core nacelle  12  that houses a low rotor  14  and high rotor  24 . The low rotor  14  supports a low pressure compressor  16  and low pressure turbine  18 . In this example, the low rotor  14  drives a fan section  20  through a gear train  22 . The high rotor  24  rotationally supports a high pressure compressor  26  and high pressure turbine  28 . A combustor  30  is arranged between the high pressure compressor  26  and high pressure turbine  28 . The low and high rotors  14 ,  24  rotate about an axis X. At least a portion of the core nacelle  12  is disposed within a fan nacelle  34 . 
         [0031]    In the examples shown, the engine  10  is a high bypass turbofan arrangement. In one example, the bypass ratio is greater than  10 , and the fan section diameter  20  is substantially larger than the diameter of the low pressure compressor  16 . The low pressure turbine  18  has a pressure ratio that is greater than  5 , in one example. The gear train  22  can be any known suitable gear system, such as a planetary gear system with orbiting planet gears, planetary system with non-orbiting planet gears, or other type of gear system. It should be understood, however, that the above parameters are only exemplary of a contemplated geared turbofan engine. That is, the examples of this disclosure are applicable to other types of engines. 
         [0032]    For the engine  10  shown  FIG. 1 , a significant amount of thrust may be provided by a bypass flow B due to the high bypass ratio. Thrust is a function of density, velocity, and area. One or more of these parameters can be manipulated to vary the amount and direction of thrust provided by the bypass flow B. A core flow C communicates from the core nacelle  12 . In one example, the engine  10  includes a nozzle structure  38  associated with the nozzle exit area A to change the physical area and geometry to manipulate the thrust provided by the bypass flow B. However, it should be understood that the nozzle exit area A may be effectively altered by other than structural changes, for example, by altering a boundary layer of the bypass flow B. Furthermore, it should be understood that effectively altering the nozzle exit area A is not limited to physical locations approximate to the exit of the fan nacelle  34 , but rather, includes altering the bypass flow B by any suitable means at any suitable location of the fan section  20 . 
         [0033]    In the example shown in  FIG. 2 , an engine restart system  54  includes multiple hinged flaps  42  arranged circumferentially about the rear of the fan nacelle  34 . The hinged flaps  42  form a portion of a control device  41 , which further includes a controller  50  in communication with actuators  46  used to manipulate the hinged flaps  42 . A detector  52  communicates information about the engine  10  to the controller  50 , for example, information that the engine  10  has shut down or relating to the startup state of the engine  10 . In one example, the detector  52  monitors the rotational speed of the low rotor  14 , which is indicative of the state of the engine  10 . The controller  50  interprets rotational speeds of the low rotor  14  below a certain level as a condition of the engine  10  indicting the engine  10  has shut down. In another example, the detector  52  monitors fuel consumption of the engine  10 . If the engine  10  experiences a drop in fuel consumption, the detector  52  communicates this information to the controller  50 , which interprets the information as a shutdown of the engine  10 . The detector  52  may be located proximate or apart from the engine  10 . The controller  50  also communicates with a driver  56 , which may be controlled by an aircraft operator. Thus, the controller  50  may operate automatically using information from the detector  52 , or may operate manually based on signals from the driver  56 . A starter  58 , such as a hydraulic starter, may be used to boost the rotational speed of the fan section  20 . 
         [0034]    The hinged flaps  42  can be actuated independently and/or in groups using segments  44 . The segments  44  and individual hinged flaps  42  can be moved angularly using actuators  46 . The control device  41  thereby varies the nozzle exit area A ( FIG. 1 ) between the hinged flaps  42  and the engine  10  by altering positions of the hinged flaps  42 . In a closed position, the hinged flap  42  is closer to the core nacelle  12  for a relatively smaller nozzle exit area A. In an open position, the hinged flap  42  is farther away from the core nacelle  12  for a relatively larger nozzle exit area A. 
         [0035]    When the engine  10  shuts down during flight, the fan section  20  will continue to rotate, or windmill, as the engine  10  moves, either by gliding or powered by additional engines. Restarting the engine  10  requires adequate compressed air to support combustion. Changing the nozzle exit area A influences the mass flow rate of airflow over the fan section  20  as a function of radial distance from the axis X. For example, increasing the size of the nozzle exit area A increases the bypass flow B and the core flow C. The increased mass flow rate exerts more force on the fan section  20  to accelerate rotation of the fan section  20 . Thus, by controlling bypass flow B and the core flow C the rotational speed of the fan section  20  is controlled. 
         [0036]    As an example, it is estimated that moving the hinged flaps  42  from a location suitable for aircraft cruising operations to an open position increases the windmilling speed of the fan section  20  about 10-20%. Increasing the windmilling speed of the fan section  20  also increases the rotational speed of the low rotor  14 , the low speed compressor  16 , and the low pressure turbine  18 . 
         [0037]    Rotational inertia of the fan section  20  forces airflow into the core nacelle  12 . The rotational inertia also contributes to rotating the low pressure compressor  16 , which compresses air in preparation for ignition. 
         [0038]    In an example method of restarting the engine  10 , communications from the controller  50  open the hinged flaps  42  to maximize the windmilling speed of the rotating fan section  20 , which also increases the rotational speed of the low rotor  14 . Next, communications from the controller  50  initiate ignition of the engine  10 . The controller  50  then readjusts the nozzle exit area A. Rotational inertia in the windmilling fan section  20  helps to compress airflow through the core nacelle  12 . Actuating the hinged flaps  42  in this way during the engine  10  restart increases the combinations of altitudes and airspeeds suitable for restarting the engine  10 . After reaching a sufficient level of compressed air, fuel flow is introduced to the compressed air, and the mixture is ignited, thereby restarting the engine  10 . 
         [0039]    Referring now to  FIG. 3  with continued reference to  FIG. 1 , illustrated is a typical flight envelope  60  for the engine  10 , that is, those combinations of altitude and airspeed suitable for operating the engine  10 . Within the flight envelope  60 , an area  64  represents combinations of altitude and speed suitable for restarting the engine without effectively altering the nozzle exit area A.  FIG. 4  represents an increased area  68  illustrating the combinations of altitude and speed suitable for restarting the typical engine when altering the nozzle exit area A. Formerly, the engine  10  may have needed starter assistance to restart at some of the altitudes and speeds included in area  68 . Of course, starter assistance may increase the likelihood of restarting the engine  10  at altitudes and airspeeds beyond those included in area  68 . 
         [0040]    In the disclosed examples, the ability to control the amount of airflow through the nozzle exit area A provides the benefit of restarting the engine  10  while in flight at increased combinations of altitudes and airspeeds. Restarts in prior designs may have required starter assistance for similar restarts. Further, although described in terms of restarts while in the air, adjusting nozzle exit area A ( FIG. 1 ) may also be used to facilitate starting the engine  10  while on the ground. 
         [0041]    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.