R. A. Burdisso
R. H. Thomas
C. R. Fuller
W. F. O'Brien
Dept. of Mech. Eng., Virginia Polytech. Inst. and State Univ., Blacksburg, VA 24061-0238
A JT15D turbofan engine is mounted in a test cell and operated to produce a fan blade passage frequency (BPF) of 2300 Hz. Twenty-seven flow disturbing rods are placed upstream of the 28 fan blades exciting to dominance the first circumferential spinning mode. A feedforward filtered-x adaptive multichannel LMS algorithm is implemented into a TMS320C30 DSP board. This three-channel controller is used to attenuate both the BPF tone and the first harmonic of the BPF (2BPF) tone components of the fan noise. The BPF and 2BPF frequency are sensed with a magnetic probe in the casing of the fan. This reference signal is an input to three adaptive finite-impulse response filters and whose outputs are fed forward to an array of 12 acoustic drivers mounted around the circumference of the engine inlet. The 12 drivers are divided into three channels of four drivers each. The far-field acoustic error information is obtained from three polyvinylidene fluoride piezoelectric polymer (PVDF) microphones placed in front of the engine. Experiments have demonstrated reductions of up to 10 dB in significant sectors. [Research supported by NASA Langley Research Center.]