Interaction of weak shock waves with random media

Abstract

Recent studies of the scattering of weak shock waves by continuous and discrete scatterers in random media, and of the flow generated in the scattering medium by shock propagation are described. Consideration of the coupling between shock propagation and vorticity and/or entropy fluctuations in a fluid is particularly difficult if the wave is of finite amplitude, for basic nonlinearities of fluid mechanics become important both in the wave propagation and in the turbulent motion. In one experiment, wave propagation through a cubical volume of incompletely and randomly mixed gases at the end of a large shock tube has been studied. In a second, interaction with a random array of discrete scatterers (small helium-filled soap bubbles) is studied in a smaller facility. Both of these flows are visualized by schlieren and shadowgraph photography. The scattered pressure field behind the initial disturbance is measured. Methods for measuring the characteristics of the “turbulence” before and after passage of the wave using laser scattering in the random medium have been developed; the laser speckle pattern at the focal plane of the schlieren system has been recorded photographically and has been analyzed with a computer-controlled photodensitometer to yield information about the scale and intensity of the inhomogeneities in the scattering medium. [Work supported by NSF.]