Hybrid Empirical/Computational Aeroacoustics Methodology for Rocket Noise Modeling

Abstract

Sound pressure level contours and spectral sound distributions around the Vega launch system are computed by means of a standard empirical model developed by NASA and a novel hybrid empirical/computational aeroacoustics approach. The empirical prediction is validated against available noise spectra measured on a scaled mock-up, showing a fairly good agreement when standard values for the model constants are used. The jet sources employed in the empirical prediction are then used to convolute a database of tailored Green's functions computed by means of a frequency-domain computational aeroacoustics code. This second approach allows the consideration of the real launch pad geometry and, in the limit of the grid resolution drawn by the acoustic wavelength, the mean flow refraction effects in the jet stream. The mean flow is supplied by a FLUENT simulation and projected onto the computational aeroacoustics grid. This is a Cartesian grid generated automatically and used in connection with an immersed-boundary approach. It is shown that the hybrid empirical/computational aeroacoustics prediction is able to explain some discrepancies observed between the experimental data and the empirical predictions. In addition, it generates a basis of elementary fields to be used in a source localization method under development in the framework of the Innovative Aerothermodynamic Configurations for Space Transport Systems research project, funded by the Italian Space Agency.