Installation: numerical investigation

Abstract

Acoustic installation effects are considered as scattering problem. Two methods to investigate them are presented. First, a fast multipole method boundary element method (FMM-BEM) which can solve the Helmholtz wave equation for full scale aircraft configurations at frequencies of some kHz. There, low Mach number potential mean flow fields can be taken into account by a so-called Taylor transformation. Second, a discontinuous Galerkin method (DGM) which solves acoustic perturbation equations (APE) for realistic mean flow fields is presented. DGM calculations are very expensive and can be performed for full scale aircrafts only at low frequencies. Its main purpose so far is to assess the accuracy of the FMM for selected cases. The Taylor-transformed Helmholtz equation is derived and the fundamentals of the FMM are introduced. Some details of the DLR FMM code FMCAS are given. The basic DGM equations are derived for the APE and some implementation details of the DLR DGM code DISCO++ are discussed. For generic geometries results of the FMM and DGM are compared and the limits of the Taylor transformation are shown. Finally, scattering results for a 1 kHz Monopole at a full scale aircraft geometry will be presented.