Numerical description of acoustic sources in airframe noise

Abstract

The origin of airframe noise in subsonic flows is mainly related to vorticity perturbations which i) interact with geometric inhomogeneities (edges, steps, slots), ii) are subject to strong convective accelerations of the mean flow, iii) are strongly amplified in magnitude due to hydrodynamic instability of the mean flow. Therefore, apart from an appropriate modeling of the vorticity perturbations (e.g. causal or stochastic), a suitable Computational Aeroacoustics (CAA) method needs to describe accurately the conversion 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 based on the high order spatial DRP scheme of Tam&Webb, the RK4 scheme in time and perfectly matched layers at the freefield boundaries of Hu.