Time-Dependent Jet Noise Computation Techniques

Abstract

The coupling of a three-dimensional, time-dependent, incompressible flow code to an acoustic analysis based on numerical solutions of the Phillips convected wave equation is discussed. A major challenge is finding techniques to accurately evaluate the noise source strength, which is expressed as a product of velocity derivatives in the Phillips equation. It is found to be advantageous to reexpress the Phillips source in a double space divergence form similar to that of Lighthill when the flow is incompressible. The validity of this approach is tested against both numerical solutions based on the more conventional time derivative source form in Lighthill’s equation and exact analytical solutions. Work in progress on developing a compressible turbulent flow code holds out the possibility of eventually using Lighthill’s integral equation directly to compute noise. Although the motivation for the current studies is to predict the noise of high speed jet flows, it should be noted that the incompressible flow code provides the capability of computing the noise of very low Mach number flows directly using Lighthill’s equation.

Past support on this project was provided by the National Aeronautics and Space Administration, Langley Research Center under Contract No. NAS1-18849 and current support by the NASA Lewis Research Center under Contract No. NAS3-26247.