Measured Effects of Turbulence on the Waveforms and Loudness of Sonic Booms

Abstract

The recent Shaped Sonic Boom Experiment yielded a large number of digital recordings of shaped and N‐wave sonic boom waveforms, all of which exhibited some degree of turbulent distortion. This digital data set provided an opportunity to test theoretical predictions of the shape of distortions, and to assess the effect of turbulence on the loudness of shaped booms. Distortions following the shocks were found to be virtually identical for the bow and tail shocks of each boom, confirming the usual explanation that the distortion is scattering of the shock waves and that turbulence may be considered to be frozen for the duration of a boom. RMS values of the distortions have been compared with the theory of S. C. Crow. The loudness reduction of shaped booms had been predicted by Plotkin to persist through turbulence, and this was found to be the case. The loudness calculations also confirmed that the benefit of reduced shock amplitude is nonlinear: there are benefits from both the reduced amplitude and from the increased shock thickness. (A full version of this paper was presented at the 2005 AIAA/CEAS Aeroacoustics Conference as AIAA‐2005‐2949.)