A spatial averaging of sonic boom waveforms

Abstract

Sonic booms generated by conventional supersonic aircraft are influenced by turbulence in the atmospheric boundary layer through which they propagate. The turbulence effects lead to random variability of the sonic boom waveforms measured on the ground, complicating the prediction of such waveforms. While some of the waveforms have been described as N-waves with spikes immediately after the shocks, others measured a few hundreds of feet away tend to be rounded. The current paper presents an analysis method that uses a spatial averaging of an ensemble of measured waveforms to obtain a mean waveform and higher-order statistical moments. The statistics obtained are anticipated to be useful in characterizing the waveforms generated by any supersonic vehicle. They will also be useful for validating theoretical and semi-empirical models used for predicting turbulence effects on sonic booms. This paper discusses the advantages and disadvantages of spatial averaging in the time domain and the frequency domain. Preliminary results indicate that the mean waveforms have rise times larger than those obtained using a sonic boom propagation model that does not account for the turbulence effects, suggesting that turbulence effects may not be ignored.