Observation and modeling of mixing-layer development in high-energy-density, blast-wave-driven shear flow

Abstract

In this work, we examine the hydrodynamics of high-energy-density (HED) shear flows. Experiments, consisting of two materials of differing density, use the OMEGA-60 laser to drive a blast wave at a pressure of ∼50 Mbar into one of the media, creating a shear flow in the resulting shocked system. The interface between the two materials is Kelvin-Helmholtz unstable, and a mixing layer of growing width develops due to the shear. To theoretically analyze the instability's behavior, we rely on two sources of information. First, the interface spectrum is well-characterized, which allows us to identify how the shock front and the subsequent shear in the post-shock flow interact with the interface. These observations provide direct evidence that vortex merger dominates the evolution of the interface structure. Second, simulations calibrated to the experiment allow us to estimate the time-dependent evolution of the deposition of vorticity at the interface. The overall result is that we are able to choose a hydrodynamic model for the system, and consequently examine how well the flow in this HED system corresponds to a classical hydrodynamic description.

Numerical simulations of a shock interacting with successive interfaces using the Discontinuous Galerkin method: the multilayered Richtmyer–Meshkov and Rayleigh–Taylor instabilities

“…Mesh generation and post-processing visualization were carried out with Gmsh, a three-dimensional finite element mesh generator with built-in pre-and post-processing facilities [15]. Our code has been used previously to simulate HEDP experiments of blast-wave-driven shear flow [13].…”

Evolution of surface structure in laser-preheated perturbed materials

“…These systems often involve a material interface with seeded interface structure, and it is often assumed or approximated that the prefabricated initial conditions and the conditions encountered by the shock are identical. This is not necessarily valid [36] and a more thorough understanding of how initial conditions evolve is important in correctly interpreting the results of these experiments. For instance, the work presented here is part of a larger experimental effort investigating shear instability in a geometry involving counterpropagating flows [37,38].…”

Observation of Single-Mode, Kelvin-Helmholtz Instability in a Supersonic Flow

“…Work producing supersonic merged flows over wedges [7] or counter-streaming supersonic flows with no seed modulation [8] generated uncontrolled, multimode initial conditions that precluded single-mode observations. Other recent work observed the growth of (random) multimode KH driven by subsonic, shear flow [9,10]. The single-mode experiment of Harding et al [11] produced rollups via a different mechanism: the baroclinic (∇ρ × ∇p) deposition of vorticity by laser-driven shock fronts, with negligible contributions from the later, subsonic shear flow.…”

“…We processed the radiographic data using an unsharpmask algorithm [10,21] to obtain the interface location, and analyzed the results to infer several quantities of interest, shown in Table I. We determined the shock location for each radiograph by locating the position where the surface of the plastic was deflected downward, and inferred the shock velocity from these observations at various times.…”