Abstract
A JT15D Pratt & Whitney engine is mounted in a test cell and operated at near idle conditions producing a fan blade passage frequency (BPF) of 2200 Hz. Flow disturbing rods are placed upstream of the fan to excite to dominance selective acoustic modes. A feedforward filtered-X adaptive LMS algorithm is implemented into a TMS320C30 DSP board. This controller is used to attenuate the BPF component of the fan noise. The BPF signal is sensed with a proximity probe placed in the plane of the inlet fan and provides the reference signal to the controller. This signal is input into an adaptive finite impulse response (FIR) filter whose output is fed forward into an array of 24 acoustic drivers attached to a ring mounted to the engine. The far-field acoustic error information is obtained from a microphone placed directly in front of the engine. The control algorithm then adjusts the phase and magnitude of the control signal to minimize the mean-square value of the error signal. Experiments have demonstrated reduction of the BPF noise component of up to 20 dB. [Work supported by NASA Langley Research Center.]
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