Surface and volme propagation methods for broadband sound prediction with synthetic turbulent sound sources

Abstract

One way to tackle the problem of noise generated aerodynamically at solid surfaces is based on surface integral methods. To capture sound radiation characteristics sufficiently accurate it is necessary to enclose with the surface the entire surface area that affects sound radiation. For airfoil trailing edge noise, for example, this means to wrap-up the entire airfoil to properly capture the multi-lobe radiation pattern. If surface data is not available everywhere, the unknowns of the problem can be obtained with the Boundary Element Method (BEM). High Helmholtz number problems such as aerodynamically generated sound refracted at full-scale aircraft become treatable with fast multi pole BEM. However, surface integral based methods cannot properly tackle refraction effects in non-uniform flow. In recent years different numerical perturbation methods have been developed for simulating the propagation of acoustic perturbations over a given non-uniform meanflow. The neglect of refraction effects can give rise to significant errors in the prediction of sound pressure levels. The applicability of stochastic methods generating synthetic turbulence for the fast prediction of turbulence related broadband sound has been studied in recent years. The coupling of synthetic turbulence methods to perturbation equations and fast multi pole BEM will be discussed.