Abstract: The invention is a method and system for fan flutter control. The output of circumferentially distributed sensors is used to calculate the asymmetry of a flow field. The asymmetry measurement is used to modulate a bleed valve, variable exhaust nozzle or other device to increase the fan's tolerance of flutter disturbances.

Abstract: The invention is a method and system for fan flutter control. The output of circumferentially distributed sensors is used to calculate the asymmetry of a flow field. The asymmetry measurement is used to modulate a bleed valve, variable exhaust nozzle or other device to increase the fan's tolerance of flutter disturbances.

Abstract: A system for controlling aeromechanical instability or flutter in turbofan engines having fan blades employs a sensor, such as an off-blade static pressure sensor or proximity detector mounted on a turbofan engine at an inlet of a rotor of the engine for generating a signal to detect resonance of the turbofan blades at frequencies associated with flutter. A controller is coupled to the sensor for generating by spatial Fourier decomposition from the sensor signal a command signal comprising a real time amplitude component and a spatial phase of disturbances of a predetermined nodal diameter and coincident with a natural frequency of resonance of a predetermined structural mode of the fan blades in the stationary frame. An actuator, such as a bleed valve or acoustic speaker, is mounted on the turbofan engine for damping flutter dynamics in response to the amplitude of the command signal.

Abstract: A pressure sensor (12) is located in the compressor stage of a gas turbine engine (10) to provide a pressure signal (PR1) that shows the compressor flow characteristics. The pressure signal (PR1) is applied to a bandpass filter (16) with roll-offs above and below N2. The difference between the filter output and a stored value for the pressure signal is integrated, and compressor bleed valves (18) are opened if the integral exceeds a stored threshold. The health of a compressor stage is determined by analyzing the magnitude of compressor pressure variations at N2 while accelerating the engine and by comparing the magnitude with values obtained from a compressor with a known stall margin.

Abstract: A technique for controlling compressor stall and surge is disclosed. In a gas turbine engine, static pressure asymmetry is sensed at a plurality of locations along the circumference of the compressor inlet. Time rate of change of the mass flow in the compressor is also estimated using pressure measurements in the compressor. A signal processor uses these signals to modulate a compressor bleed valve responsive to the level of flow property asymmetry, the time rate of change of the annulus average flow to enhance operability of the compressor.