Aeroacoustic catastrophes: upstream cusp beaming of jet noise Seminar

In this seminar, we outline the development of a comprehensive novel ray solver for the prediction of noise from turbulent jet flows. Ray methods offer a quick, robust and accurate platform capable of calculating flow-acoustic interaction effects for any jet flow, for example, those that may arise from asymmetric nozzle geometries in a noise optimisation study. We show how caustics, ubiquitous singularities of the ray field, and complex rays required for the propagation of evanescent waves such as those found in the cone of silence (a region of exponential decay), may both be computed by an appeal to Thom’s catastrophe theory.

Using this approach, we discuss the discovery of a new mechanism by which noise from asymmetric jets may not only be beamed upstream against the jet flow, in advance of the aircraft, but also directed down towards the ground along a broad cusp-shaped front. Crucially, this new upstream beaming noise is of comparable magnitude to the downstream emissions. Hence, under suitable conditions, the very asymmetric geometries designed to minimise downstream noise emissions may, inadvertently, prolong the exposure to noise and increase the annoyance. This also poses issues for noise certification measurements, which are currently focused on the measurement of downstream noise emissions.