Active control of buzz-saw tones: Experimental results from a laboratory-scale, no-flow rig

This paper details the results of an experiment on a small scale no-flow rig to control a spinning mode with similar characteristics to the modes generated by buzz-saw noise. The spinning mode (m=−3, n=1) is generated by a mode synthesizer ring which has similar characteristics to that of a low frequency buzz-saw mode. A control system using seven microphones and seven control actuators is used to minimize the sum of the squared pressures at the duct wall using a filtered reference least mean squares (FXLMS) algorithm. It is shown that at certain frequencies the sound power transmitted to the duct termination is reduced by 14.5dB. The control mechanisms at different frequency ranges are identified and discussed with reference to computer simulations. It is shown that cut-off modes excited by the secondary actuator array have a significant effect on control performance at frequencies close to the cut-on frequency of the (m=−4, n=1) mode.