Jet noise prediction using the Lighthill acoustic analogy

A jet noise source model based on the Lighthill acoustic analogy is presented. Although much of the theory used is well known, a new feature of the model is the inclusion of frequency dependence for the time and length scales used in the turbulence two-point correlation function. It is found that allowing for this experimentally observed dependence markedly improves the agreement of the model's prediction with experimental far-field data. To illustrate this agreement the case of a single turbulent jet is considered. Using well-respected scaling laws for the mean and turbulent properties of such jets a prediction for a single jet noise spectrum is obtained which shows very good agreement with the prediction using the empirically based ESDU database. The effect of altering the frequency dependence of the moving axis timescale is briefly discussed and it is indicated how the source model can be generalized to use RANS and other CFD data to predict jet noise, for single and coaxial jets and also for more novel nozzle geometries.