Revisiting the frozen gust assumption through the aeroacoustic scattering of wavepackets by a semi-infinite plate

One of the main sources of aerodynamic noise is the interaction of boundary-layer turbulence with a wing trailing edge. The aeroacoustic theory used to predict this trailing-edge noise is often based upon the `frozen gust' assumption, which posits that boundary-layer vorticity is unaffected by the flow field local to the trailing edge. This classical theory has been successful for straight edges, but the agreement between predictive theory and computational or experimental results is often poor for serrated or other geometrical variations to the trailing edge. Several computational studies have shown that trailing-edge serrations affect the vorticity field around the edge, suggesting that the frozen gust assumption might not be valid there. In the current research we develop an analytical model to predict the noise scattered by a traveling wavepacket passing near the edge of a semi-infinite flat plate. The solution is derived in the time domain for a wavepacket of either constant or spatially varying wavenumber, which allows us to examine the effect of relaxing the frozen gust assumption on the prediction of trailing-edge noise. Our results shed light on the role that spatial variations in the vorticity field local to the trailing edge have on the far-field scattered noise.