Acoustic Analogy and Alternative Theories for Jet Noise Prediction

TLDR

Jet noise prediction mainly relies on Lighthill’s or Lilley’s acoustic analogy, with a single alternative model by Tam and Auriault, and all approaches require assumptions about turbulent source statistics. The study proposes a refined acoustic analogy to better identify equivalent source mechanisms and discusses remaining noise‑prediction issues. The authors compute turbulence scales from RANS solutions using a kappa‑sigma turbulence model. For equivalent empirical assumptions, Tam and Auriault’s model matches experimental noise better than the acoustic analogy, but when consistent assumptions are used both approaches predict identical noise.

Abstract

Several methods for the prediction of jet noise are described. All but one of the noise prediction schemes are based on Lighthill's or Lilley's acoustic analogy, whereas the other is the jet noise generation model recently proposed by Tam and Auriault. In all of the approaches, some assumptions must be made concerning the statistical properties of the turbulent sources. In each case the characteristic scales of the turbulence are obtained from a solution of the Reynolds-averaged Navier-Stokes equation using a kappa-sigma turbulence model. It is shown that, for the same level of empiricism, Tam and Auriault's model yields better agreement with experimental noise measurements than the acoustic analogy. It is then shown that this result is not because of some fundamental flaw in the acoustic analogy approach, but instead is associated with the assumptions made in the approximation of the turbulent source statistics. If consistent assumptions are made, both the acoustic analogy and Tam and Auriault's model yield identical noise predictions. In conclusion, a proposal is presented for an acoustic analogy that provides a clearer identification of the equivalent source mechanisms, as is a discussion of noise prediction issues that remain to be resolved.