Numerical description of acoustic sources in airframe noise

The origin of airframe noise in subsonic flours is mainly related to vortic ity perturbations which i) interact with geometric inhomogeneities (egdes, steps, slots), ii) are subject to strong convective accelerations of the me an flow, iii) are strongly amplified in magnitude due to hydrodynamic insta bility of the mean flow. Therefore, apart from an appropriate modeling of t he vorticity perturbations (e.g. causal or stochastic), a suitable Computat ional Aeroacoustics (CAA) method needs to describe accurately the conversio n process from hydrodynamic to acoustic perturbations, i.e. the very noise generation. Aeronautics-related examples of numerically simulated airframe noise phenomena are presented which were obtained using DLR's CAA-code base d on the high order spatial DRP scheme of Tam xi Webb [1], the RK4 scheme i n time and perfectly matched layers at the freefield boundaries Hu [2].