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Jul 2008

Volume 124, Issue 1, pp. 1-EL13

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Evidence of wave front folding of sonic booms by a laboratory-scale deterministic experiment of shock waves in a heterogeneous medium

Lili Ganjehi, Régis Marchiano, François Coulouvrat, and Jean-Louis Thomas

J. Acoust. Soc. Am. Volume 124, Issue 1, pp. 57-71 (2008); (15 pages) | Cited 1 time

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Show Abstract
The influence of the planetary boundary layer on the sonic boom received at the ground level is known since the 1960s to be of major importance. Sonic boom propagation in a turbulent medium is characterized by an increase of the mean rise time and a huge variability. An experiment is conducted at a 1:100 000 scale in water to investigate ultrasonic shock wave interaction with a single heterogeneity. The experiment shows a very good scaling with sonic boom, concerning the size of the heterogeneities, the wave amplitude, and the rise time of the incident wave. The wave front folding associated with local focusing, and its link to the increase of the rise time, are evidenced by the experiment. The observed amplification of the peak pressure (by a factor up to 2), and increase of the rise time (by up to about one magnitude order), are in qualitative agreement with sonic boom observations. A nonlinear parabolic model is compared favorably to the experiment on axis, though the paraxial approximation turns out less precise off axis. Simulations are finally used to discriminate between nonlinear and linear propagations, showing nonlinearities affect mostly the higher harmonics that are in the audible range for sonic booms.
Show PACS
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
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