Robin O. Clevel
Appl. Res. Labs., P.O. Box 8029, Austin, TX 78713-8029
Sonic-boom propagation is affected by stratification, geometrical
spreading, nonlinear distortion, absorption and dispersion, and turbulence.
Stressed in this paper is stratification, in particular its indirect effect on
distortion and absorption. The stratification of the density and sound speed
leads to refraction and impedance variation, which play a major role in
determining the amplitude of the waveform on the ground. Stratification, and
associated spreading, can also control the amount of nonlinear distortion a
sonic boom suffers. In extreme cases the amount of nonlinear distortion is
finite---a phenomenon known as waveform freezing. Analysis shows that for
aircraft in the lower 20 km of the atmosphere waveform freezing does not occur.
Through their dependence on temperature, pressure, and humidity, absorption and
dispersion are also stratified. A new time domain algorithm, based on a
Burgers-type equation, was developed to analyze the effect of the
stratification of absorption [