Variable area fan nozzle with drive system health monitoring

#Typical aircraft turbofan jet engines include an engine core, a nacelle that surrounds the engine core, and a fan that draws in a flow of air that is split into bypass airflow and engine core airflow. The nacelle provides a bypass duct that surrounds the engine core. The bypass airflow is transported through the bypass duct. The nacelle is configured to promote laminar flow of air through the bypass duct. The engine core includes a multi-stage compressor to compress the engine core airflow, a combustor to add thermal energy to the compressed engine core airflow, and a turbine section downstream of the combustor to produce mechanical power from the engine core airflow. The typical turbine section has two and sometimes three turbine stages. The turbine stages are used to drive the compressor and the fan. After exiting from the turbine section, the engine core airflow exits through an exhaust nozzle at the aft end of the engine.

#In a turbofan engine, the fan typically produces a majority of the thrust produced by the engine. The bypass airflow can be used to produce reverse thrust typically used during landing. Thrust reversers mounted in the nacelle selectively reverse the direction of the bypass airflow to generate reverse thrust. During normal engine operation, the bypass airflow may or may not be mixed with the exhausted engine core airflow prior to exiting the engine assembly.

#Several turbofan engine parameters have a significant impact upon engine performance. Bypass ratio (BPR) is the ratio of the bypass airflow rate to the engine core airflow rate. A high BPR engine (e.g., BPR of 5 or more) typically has better specific fuel consumption (SFC) and is typically quieter than a low BPR engine of equal thrust. In general, a higher BPR results in lower average exhaust velocities and less jet noise at a specific thrust. A turbofan engine's performance is also affected by the engine's fan pressure ratio (FPR). FPR is the ratio of the air pressure at the engine's fan nozzle exit to the pressure of the air entering the fan. A lower FPR results in lower exhaust velocity and higher propulsive efficiency. Reducing an engine's FPR can reach a practical limit, however, as a low FPR may not generate sufficient thrust and may cause engine fan stall, blade flutter, and/or compressor surge under certain operating conditions.

#FIG. 1 is a perspective view illustration of a turbofan engine that includes a variable area fan nozzle (VAFN) assembly, in accordance with many embodiments.

#FIG. 2 is a cross-sectional view of the turbofan engine of FIG. 1.

#FIG. 3 is an end view of the turbofan engine of FIG. 1.

#In the following description, various embodiments of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the present invention can be practiced without the specific details. Furthermore, well-known features may be omitted or simplified in order not to obscure the embodiment being described.

#Referring now to the drawings, in which like reference numerals represent like parts throughout the several views, FIG. 1 shows a turbofan engine 10 that includes a variable area fan nozzle (VAFN) assembly 12 having a translating fan nozzle 50 that can be selectively adjusted, for example, as the engine 10 operates under different flight conditions. As discussed above, such an adjustment can be used to optimize the engine's performance. As shown in FIG. 2, the translating fan nozzle 50 can be selectively translated (i.e., moved fore and aft) to vary the fan nozzle's exit area 52 and to adjust how much of the bypass airflow exits through an upstream exit 60 formed by the VAFN assembly 12. For example, when the translating fan nozzle 50 is in the stowed position, the upstream exit 60 is closed and the exit area 52 is minimized, thereby maximizing the fan pressure ratio (FPR) for a particular operational condition. And when the translating fan nozzle 50 is in the fully deployed position, the upstream exit 60 opening is maximized and the exit area 52 is maximized, thereby minimizing the FPR for the particular operational condition. Accordingly, selectively positioning the translating fan nozzle 50 can be used to selectively vary the FPR. And varying the FPR can be used to optimize engine performance, increase fan stall margins, avoid engine malfunction, and/or avoid engine shutdown. For purposes of illustration, the VAFN assembly 12 is shown in the context of a turbofan aircraft engine 10. The engine 10 can be mounted to a wing or fuselage of an aircraft, for example, by a pylon or other similar support (not shown in the figures).

#The engine 10 includes an engine core 16 and a nacelle 18. The engine core 16 is housed in a core cowl 19. As shown in FIG. 2, a fan 20 is mounted adjacent to an upstream end of the nacelle 18, and includes a series of fan blades 22 that are rotated about the engine centerline CL during engine operation so as to draw a flow of air into an inlet end 26 of the engine 10. An annular bypass duct 24 is defined between the engine core 16 and the nacelle 18. The airflow drawn into the engine 10 is accelerated by the rotating fan blades 22. A portion of the airflow is directed into and through a multi-stage compressor (not illustrated) within the engine core 16. The engine core airflow through the engine core 16 is initially passed through the compressor to increase the airflow pressure, after which the pressurized air is passed through a combustor (not shown), where it is mixed with fuel and the mixture ignited. The combustion of the fuel and air mixture within the combustor causes the air to expand, which in turn drives a series of turbines at the rear of the engine, indicated generally at 38, to rotate and in turn to provide power to the fan 20.