Sonic Boom Propagation in an Unsteady Atmosphere

Abstract

A review is given of information obtained in recent years concerning the effects of atmospheric unsteadiness on sonic boom signatures. These effects include the observed random variations in boom overpressures from those expected for a stratified atmosphere, the anomalously large and variable risetimes, and the occurrence of spiked or rounded waveforms rather than the characteristic N waves. The extent of the variability in data recorded during actual flight tests is summarized in the form of histograms, representing experimentally obtained probability density functions. The physical mechanisms believed to be responsible for the variations and the anomalous features in the signatures are described. These include refraction and subsequent wavefront rippling by turbulence, the possible focusing or defocusing of rays, the formation of caustics and the phenomenon of wavefront folding, and diffraction. Recent statistical theories of shock propagation through a turbulent atmosphere proposed by Crow, Plotkin and by George, Pierce, and Horning are reviewed.