Multi-exposure flow visualization experiments with laser-sheet illumination provide growth-rate measurement of Richtmyer–Meshkov instability of a thin, perturbed heavy-gas layer embedded in a lower-density gas and accelerated by a planar shock wave. The measurements clearly show the three-stage transition to turbulence of this gas-curtain instability and the single-event coexistence of the three primary flow morphologies discovered previously. The shock-induced circulation for each event is estimated using a simple model based on Richtmyer–Meshkov instability and an infinite linear array of vortex points. These estimates are consistent with simplified flow simulations using a finite-core vortex-blob model.

Richtmyer-Meshkov instability of a thin curtain of heavy gas (SF 6) embedded in air and accelerated by a planar shock wave ͑Mach 1.2͒ leads to the growth of interfacial perturbations in the curtain and to mixing. Our experiments produce a phenomenological description of the mixing transition and incipient turbulence during the first millisecond after the shock interaction. Growth of scales both larger and smaller than that of initial perturbations is visually observed and quantified by applying a wavelet transform to laser-sheet images of the evolving gas curtain. Histogram and wavelet analyses show an abrupt mixing transition for a multimode initial perturbation that is not apparent for single-mode perturbations.

We experimentally investigate the evolution and interaction of two Richtmyer-Meshkov-unstable gas cylinders using concentration field visualization and particle image velocimetry. The heavy-gas (SF 6) cylinders have an initial spanwise separation of S/D ͑where D is the cylinder diameter͒ and are simultaneously impacted by a planar, Mach 1.2 shock. The resulting flow morphologies are highly reproducible and highly sensitive to the initial separation, which is varied from S/DϷ1.2 to 2.0. The effects of the cylinder-cylinder interaction are quantified using both visualization and high-resolution velocimetry. Vorticity fields reveal that a principal interaction effect is the weakening of the inner vortices of the system. We observe a nonlinear, threshold-type behavior of inner vortex formation around S/Dϭ1.5. A correlation-based ensemble-averaging procedure extracts the persistent character of the unstable flow structures, and permits decomposition of the concentration fields into mean ͑deterministic͒ and fluctuating ͑stochastic͒ components.

The interaction of a dilute dispersed cloud of microbubbles with a planar free-shear layer is investigated experimentally. The emphasis of this study is on the role of the coherent large scales of the flow in the bubble dispersion field and the energy redistribution within the carrier phase. The interphase momentum transfer integrals that appear in the volume-averaged momentum and energy equations account for redistribution of energy from potential to kinetic within the carrier phase. This results from both the hydrostatic and dynamic pressure fields. The energy redistribution within the carrier phase that is associated with the large-scale structures of the flow possesses significant inhomogeneities within the mixing layer. Peaks of enhanced kinetic energy generation are associated with the upwelling regions at the downstream edge of the coherent vortex cores, and weaker peaks of kinetic energy destruction are associated with downwelling regions. The contribution of the quasi-steady drag term to the total energy redistribution is found to be dominant in only a limited region of the flow field.