ACTIVE FLOW CONTROL TO REDUCE FAN BLADE VIBRATION AND NOISE

An experimental investigation is conducted to reduce the unsteady stator-rotor interaction in a turbofan simulator using active flow control. The fan rotor of a l/lCscale turbofan propulsion simulator is subjected to circumferentially periodic inlet flow distortions, generated by four stators that support a centerbody in the inlet mounted onto the simulator. These wakes are re-energized by injecting air from the trailing edge of each stator through discrete blowing holes. The flow rate through each blowing hole is controlled by individual MEMS (Micro-Electra-Mechanical-System) based microvalve. The microvalve actuation signal voltage is generated by a PID (Proportional Integral and Derivative) controller and is a function of the wake velocity defect. Far-field Sound Pressure Level (SPL) at the Blade Passing Frequency (BPF) without and with blowing is measured in an anechoic chamber. The experiments are performed for two simulator speeds of 29,500 ‘pm and 40,000 rpm. Wake reenergization produces significant reductions in the BPF tone at both speeds. The sound power level at the BPF calculated from measured far-field directivity shows that source power is reduced by at least half The feasibility and advantage of active control is demonstrated by the ability of the system to respond to changes in the inlet flow velocity.