An experimental study of the flow after shock interactions with cylindrical helium inhomegeneities

Abstract

A shock traveling in air interacts with a laminar jet of helium flowing normal to the direction of shock propagation. Planar laser Rayleigh scattering is used to study the deformation and motion of the originally circular jet cross-section. The velocity of the jet before the shock interaction is much less than the velocities generated by the shock wave. Thus, the helium jet serves to create a cylindrical bubble of a lighter density gas imbedded in a heavier one. Four different shock Mach numbers (1.066, 1.14, 1.5, and 2.0) are studied. Two different jet/air density ratios are examined by using pure helium in the jet in one case, and a mixture of airlhelium in the other. After the shock interaction, a vortex pair forms from the baroclinically generated vorticity. The experiments measure the velocity of the helium relative to the surrounding air, the spacing between the vortex cores, and the circulation of the vortices. Experiments viewing the reflected shock interaction are also performed. Excellent agreement is found with previous computational studies.