Jet noise: sound generation by disc and cylinder sources

An exact analysis of the field radiated by tonal and random non-axisymmetric sources distributed over a disc or cylinder is presented. The analysis is exact, without recourse to near- or far-field approximations, and leads to a direct relationship between source frequency and the nature of the radiated field. The implications of the analysis for a number of applications are discussed, finding in particular that source identification is inherently ill-conditioned as a result of a ‘filtering’ effect that removes information from the radiation field; low-frequency sources generate fields that are indistinguishable from each other; jet noise fields are inherently simpler than the flow that gives rise to them, a finding that has previously been noted for experimental data.