Acoustic and flow measurements of porous plate designs for aerodynamic noise mitigation

The acoustic and flow effects of flat plates with chordwise perforations are experimentally investigated. A dimensionless parameter known to control the scaling of noise generation in a quiescent fluid is applied to the analysis of sound generated by a turbulent boundary layer over the flat plates. Multiple perforation designs are tested and compared to a nonporous reference plate in an open jet aeroacoustic wind tunnel. DAMAS acoustic beamforming is performed in the trailing-edge region and other sectors of the plate, and the flow field of the plates is investigated using hot-wire anemometry measurements in the near-wake and boundary layer. An increase in the porosity parameter leads to an decrease in noise generation at low frequencies and an increase at high frequencies for the porosity designs considered. In particular, sound pressure levels of the trailing edge region are reduced by up to 20 dB at low frequencies and are increased by up to 18 dB at high frequencies. The presence of porosity increases the turbulence intensity near the plate surface, which may be responsible for the observed high-frequency excess noise created by the pores themselves. Nevertheless, trailing-edge porosity is shown to reduce the overall sound pressure level by up to 4 dB.