Prediction of jet mixing noise with Lighthill's Acoustic Analogy and geometrical acoustics

A computational aeroacoustics prediction tool based on the application of Lighthill’s theory is presented to compute noise from subsonic turbulent jets. The sources of sound are modeled by expressing Lighthill’s source term as two-point correlations of the velocity fluctuations and the sound refraction effects are taken into account by a ray tracing methodology. Both the source and refraction models use the flow information collected from a solution of the Reynolds-Averaged Navier-Stokes equations with a standard k-epsilon turbulence model. By adopting the ray tracing method to compute the refraction effects a high-frequency approximation is implied, while no assumption about the mean flow is needed, enabling us to apply the new method to jet noise problems with inherently three-dimensional propagation effects. Predictions show good agreement with narrow-band measurements for the overall sound pressure levels and spectrum shape in polar angles between 60 and 110 degrees for isothermal and hot jets with acoustic Mach number ranging from 0.5 to 1.0. The method presented herein can be applied as a relatively low cost and robust engineering tool for industrial optimization purposes.