TOWARD THE DIRECT CALCULATION OF NOISE - FLUID ACOUSTIC COUPLED SIMULATION/

A numerical technique for the direct calculation of how generated nois e is developed in this paper and applied to the prediction of superson ic 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 compres sible Navier-Stokes equations in the first step. Flow perturbations ba sed on the description of the large-scale structures as a linear super position of normal mode instability waves are introduced at the nozzle exit plane. Their propagation in time and space are studied through s olution of the Euler equations for the perturbations in the second ste p. Such an approach ensures that the fluctuation variables, which may be several orders of magnitude smaller than the mean values, are compu ted accurately without numerical round-off errors. Some dynamic featur es 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 sou nd are examined.