Analytical investigation of active control of radiated inlet fan noise

Abstract

An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject antinoise into the duct to destructively interfere with the tonal sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the disturbance and the control sources is based on duct modal expansion. Attenuation of the radiated sound field is accomplished using a multiple-channel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The model is used to evaluate the performance of the control system for single and multiple circumferential arrays of control sources. The model can be extended for use in design optimization. Sample results are presented to illustrate the predicted sound attenuations.