On the noise generated by a controlled-diffusion aerofoil at [formula omitted

Abstract

A compressible direct numerical simulation of the flow and near-field acoustics over a Controlled-Diffusion aerofoil at 8∘ geometrical angle of attack, a Reynolds number of Rec=1.5×105 based on the chord and a free-stream Mach number of M=0.25, with a spanwise extent of 12% chord was conducted to produce a space-time database to determine the aerofoil noise generation mechanisms. Three main noise sources respectively from the flow separation and reattachment at the leading-edge on the suction side, the interaction between the attached turbulent flow on the suction side and the trailing-edge and an additional near-wake source due to secondary instability are observed. It should be noticed, however, that such an additional source may strongly depend on the aerofoil shape and also on the flow conditions. The contribution of these three noise sources to the noise radiation at different frequencies is analysed through a wavenumber-frequency filtering procedure. In the low to mid frequency range, the contribution of the traditional trailing-edge noise is significant, whereas at high frequencies, the noise radiation is shown to be related to the flow transition/reattachment in the leading-edge area and the flow in the near wake further downstream of the trailing-edge noise source center. The near-wake source is observed to dominate the high-frequency noise radiation.