Far-Field Dipole Noise Extracted From Time-Resolved PIV Over Separated Aerofoils

We demonstrate far-field dipole acoustics from time-resolved planar particle image velocimetry (PIV) data for turbulent separated flow over NACA 0012 and NACA 65-410 aerofoils at a chord-based Reynolds number Re_c ≈ 71000. The efficacy of the pressure reconstructions is demonstrated through a comparison with RANS simulationsand surface pressure power spectra. The pressure reconstructions are used in combination with Curle's analogy to determine the far-field noise generation. The noise directivity is found to be determined mostly by the geometry, with similar overall sound power level for both aerofoils. Through use of the data-driven spectral Linear Stochastic Estimation (sLSE) technique, the turbulent structures most correlated to the farfield noise are identified. In transient stall conditions, the location of correlated structures suggests shear layer flapping as the dominant mechanism. In deep stall, the correlated structures are concentrated further downstream in proximity to the trailing edge.