Toward the direct calculation of noise - Fluid/acoustic coupled simulation

A numerical technique for the direct calculation of flow generated noise is developed in this paper and applied to the prediction of supersonic jet noise. In this approach, each flow parameter is decomposed into a time-averaged mean and a time-dependent fluctuating part. The mean flow is established with the solution of the three-dimensional compressible Navier-Stokes equations in the first step. Flow perturbations based on the description of the large-scale structures as a linear superposition of normal mode instability waves are introduced at the nozzle exit plane. Their propagation in time and space are studied through solution of the Euler equations for the perturbations in the second step. Such an approach ensures that the fluctuation variables, which may be several orders of magnitude smaller than the mean values, are computed accurately without numerical round-off errors. Some dynamic features of the jet flow are presented. Predictions of radiated noise for a few test cases and qualitative comparisons with experiments are made. Effects of jet temperature on the peak directivity of the radiated sound are examined.