Extremum-Seeking Control of Jet Noise

Abstract

An extremum-seeking algorithm is used to optimise a fluidic jet-noise controller. The control device, called a fluidevron, produces reductions in jet noise that are comparable with those achieved using conventional microjets, but the underlying flow-physics have been found to be different (Laurendeau et al. [1]). The extremum-seeking algorithm is used to optimise the control either for maximum low-frequency noise-reduction, or for maximum overall noise-reduction. This is achieved through a specification of the frequency-range over which noise reduction is sought. The extremum-seeking performs well, producing integrated low-frequency noise reduction gains on the order of 2.5 dB at 60 degrees (angle measured with respect to the dowstream jet axis) when tuned for maximum low-frequency benefit, and an overall reduction of 1.5 dB, where the high frequency penalty is virtually eliminated, when tuned for maximum spectral range. Farfield microphone spectra at different polar stations show that the control effect is omnidirectional. This implies that there is no directional bias in the response of the source mechanisms to the actuation. Finally, the relationship between noise reduction and flow-rate is studied and found to be non-linear. The source mechanisms are most receptive at low flow-rate, a saturation point being reached after which the actuation no longer has control authority over the source dynamics.