Recovering the spatial correlation of liftoff acoustics from the Ares Scale Model Acoustics Test

Accurately predicting structural vibrations due to acoustic loads requires knowledge about the overall sound pressure levels, the amplitude of the sound pressure levels as a function of frequency (auto-spectra), and the spatial correlation of the sound pressure levels (cross-spectra). When dealing with the liftoff acoustics of launch vehicles, a large amount of historical data is available in terms of overall levels and auto-spectra, but only a limited amount of data exists for cross-spectra. ATA Engineering has used data taken during NASAs Ares Scale Model Acoustic Test to recover the spatial correlation of liftoff acoustics for a typical launch vehicle. By assuming the measured liftoff acoustics that are a combination of propagating waves and diffuse acoustic fields, curve-fitting algorithms are used to recover spatial correlation parameters required by modern vibro-acoustic analysis software.