Advances in numerical simulation of sonic boom in realistic atmospheres

Abstract

Efficient and accurate numerical simulation of sonic boom is a key issue for both the design of low boom aircraft and the definition of a standard on supersonic overland flights. Atmospheric turbulence is known since the 1960s to significantly alter the ideal N-wave boom waveform. Such random fluctuations cannot be reproduced by the standard ray tracing method. Neither can it simulate the lateral boom beyond the geometrical carpet edge. There occur many non-geometrical features such as creeping waves, wave guiding or scattering. To progress in the direction of boom simulation beyond the geometrical approximation, we developed the so-called FLHOWARD3D software. For accuracy, it can handle 3D temperature, density or wind heterogeneities, atmospheric absorption, and nonlinear propagation effects. For efficiency, a one-way approximation is performed, neglecting the backscattered field. Nevertheless, the forward field satisfies an accurate dispersion relation, even in moving atmospheres. Involved physical effects are handled separately by optimized algorithms, combined by a second-order split-step approach. The resulting software is parallelized using the MPI paradigm. The performances of the software will be illustrated by two cases: boom scattering by turbulence, and lateral boom propagation in case of temperature inversion. This last case will be compared with flight test data.