Aerofoil tonal noise reduction using serrated trailing edges

A symmetric Joukowski aerofoil with 12% thickness is investigated via a wall-resolved largeeddy simulation at Re1 = 250 000, M1 = 0.4 and zero angle of attack. The principal aim is to study the tonal noise reduction on the acoustic feedback loop event achieved by using serrated trailing edge. The acoustic feedback tone matches with 2% deviation the theory developed by Arbey and Bataille [1]. The paper retrieves the results proposed by Chong and Joseph [2] in which they emphasize the capability of serrated trailing edge in reducing aerofoil tonal noise. Two serration geometries are compared to a reference straight trailing edge and it is found that sharper serrations produce weaker sound waves in the far-field with a peak attenuation of 10 dB at the tonal frequency. Furthermore, the present work provides an unprecedented insight in the tonal noise reduction mechanisms which are twofold: 1) the scattering of wall pressure fluctuations into sound at the trailing edge is damped in the presence of serrations and 2) the spanwise coherence of the wall pressure phase breaks down earlier while using serrations therefore causing destructive interferences to the acoustic feedback loop.