Active Control of Radiated Inlet Noise from Turbofan Engines

An active control system has been applied to an operational turbofan engine to reduce tonal inlet noise produced by the fan. Flow disturbing rods placed upstream of the fan assembly excite to dominance selective acoustic modes. An array of loudspeakers mounted on the inlet of the engine create the active, or secondary sound field that destructively interferes with the fan noise. The control system, an adaptive feedforward approach utilizing a Filtered-X Least Mean Square (LMS) algorithm, obtains error information via large area transducer microphones placed in the acoustic far-field. Born a single-input, single-output (SISO) and three channel, multi-input, multi-output (MIMO) controller versions were developed. Experiments have demonstrated tonal noise reduction of up to 16 dB over large sectors in the forward direction of the turbofan inlet.