Analytical investigation of active control of radiated inlet noise from turbofan engines

TR Number



Journal Title

Journal ISSN

Volume Title


Virginia Tech


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 anti-noise into the duct to destructively interfere with the sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the fan disturbance and the control sources is based on duct modal expansion. Numerical analyses are presented for different system configurations of secondary control sources and error sensors. Two error sensing strategies are considered in this work. The first approach uses microphones placed in the acoustic far field. The second sensing technique consists of placing distributed error sensors in the engine inlet. Attenuation of the radiated sound field is accomplished using a multichannel 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 performance of selected system configurations are discussed and the sensitivity to system parameter variation to the control of inlet noise is explored. Reductions in the radiated sound power level of 4 to nearly 28 dB is demonstrated. It is also demonstrated that for global attenuation of the far field pressure multiple axial arrays of control sources are required. The model can be used to evaluate performance envelopes for various system configurations including sensitivities to error sensor and control source locations, control channel configurations and the effects of mean flow within the inlet duct. The model can also be extended for use in design optimization.