Computation of aeroacoustic scattering effects

Abstract

Scattering and diffraction phenomena are important problem in aeroacoustics. For this reason, some of the advanced numerical methods developed in Computational Fluid Dynamics are being extended for solving acoustic scattering and diffraction problem involving complex boundaries. Two computational codes have been developed in Boeing for this purpose. One of the codes is based on an unsteady panel method (also known in the literature BS the boundary element method), which becomes very expensive even at a moderately low frequency, e.g. the fundamental blade passage frequency. A more efficient code, based on a combination of several numerical methods, is also being developed to reduce computing costs. Predictions from these two codes have been checked out against analytic solutions and laboratory test data on scattering of a plane wave, and a point source by a cylinder, and a dipole source at the trailing edge of an airfoil. The results indicate that acoustic scattering and diffraction from bodies of arbitrary shapes can be efficiently predicted by codes based on advanced computational methods. It is expected that advances in computational aeroacoustics will reduce some of the empiricism in the field of prediction of aircraft noise, and help us better understand wind tunnel and flight test data.