Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session LD: Richtmeyer-Meshkov Instabilities |
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Chair: Devesh Ranjan, Los Alamos National Laboratory Room: 002B |
Monday, November 24, 2008 3:35PM - 3:48PM |
LD.00001: Experimental analysis of re-shocked gas curtain Devesh Ranjan, B.J. Balakumar, Greg Orlicz, Katherine Prestridge, Christopher Tomkins Results are presented from experiments studying the interaction of a planar shock wave of strength $M \sim $1.2 with a thin fluid layer of SF$_{6}$ gas imbedded in air. Flow visualizations are obtained using planar laser diagnostics (simultaneous PLIF/PIV measurements) rather than integral measures. A concurrent study at the lab has shown that the interaction of first shock wave with the thin fluid layer does not lead to a fully-developed turbulence stage, during the investigation window, for low-Mach number experiments. Therefore, this study is primarily focused on the turbulent mixing induced by the reshock of an already shocked interface. As the shock wave reflected from the end-wall of the test section passes through the already evolving SF$_{6}$ layer, the intense vortical and nonlinear acoustic phenomenon are observed, including dramatic changes in the length scales and topology of the evolving mushroom structures, intense mixing, and finally transition to the fully-turbulent stage characterized by fine scales in the flow field. The location of end-wall is changed during the experiments to achieve reshock of the interface at different times (different initial conditions). [Preview Abstract] |
Monday, November 24, 2008 3:48PM - 4:01PM |
LD.00002: Memory of Initial Conditions in Shocked and Re-shocked Heavy-Gas Curtains Christopher Tomkins, B.J. Balakumar, Greg Orlicz, Devesh Ranjan, Kathy Prestridge We experimentally investigate the memory of initial conditions in the concentration fields of Richtmyer-Meshkov-unstable flows. We consider shocked heavy-gas curtains in air for several initial conditions at Ma = 1.2. The concentration of the heavy gas is measured using planar laser-induced fluorescence, and spanwise power spectra of the concentration fields are computed from the PLIF data. The periodic initial conditions leave a clear imprint in the spectra as forcing modes, and the evolution of these modes is tracked over time. The effects of a stronger initial shock (Ma = 1.5), a second incident shock, and variations in the initial conditions on the persistence of the forcing modes in the spectra are investigated. [Preview Abstract] |
Monday, November 24, 2008 4:01PM - 4:14PM |
LD.00003: Turbulence Statistics in a Richtmyer-Meshkov Unstable Thin Fluid Layer after Reshock B.J. Balakumar, Greg Orlicz, Devesh Ranjan, Chris Tomkins, Kathy Prestridge We present true ensemble-averaged turbulence measurements of the density, velocity and density-velocity cross-statistics in a Richtmyer-Meshkov unstable varicose fluid layer after reshock. The instantaneous fields that comprise the ensemble at various times are obtained using high resolution simultaneous PIV-PLIF diagnostics employed on a repeatable fluid layer subjected to a Mach 1.2 shock and a subsequent reflected reshock. Sufficiently after reshock, the profiles of the density self-correlation show a double-peak structure, with the location of the peaks coinciding with the edges of the turbulent structure. The RMS of the fluctuating streamwise and spanwise velocities across the layer are observed to carry similar magnitudes pointing to a tendency of the flow to attain homogeneity. For the first time, experimentally measured density-velocity correlations will be presented to complete all the components of the 2D Reynolds stress tensor. Errors associated with the light propagation through the inhomogeneous turbulent medium, and the effects of different averaging procedures used in the calculation of the turbulence statistics will be evaluated to provide tight bounds on the present measurements. Finally, the connections of the various measurements to terms in the equations for the mass flux, kinetic energy and density self-correlation will be exemplified. [Preview Abstract] |
Monday, November 24, 2008 4:14PM - 4:27PM |
LD.00004: Simulations of a Reshocked Varicose Gas Curtain C.A. Zoldi-Sood, R.A. Gore, B.J. Balakumar, G.C. Orlicz, D. Ranjan, C.D. Tomkins, K.P. Prestridge The evolution of a varicose curtain of SF$_{6}$ gas accelerated by a Mach 1.2 shock wave in air and then reshocked 600 $\mu $s later has been examined both experimentally and computationally. Two-dimensional simulations incorporating the experimental initial conditions have been performed using RAGE, an adaptive-mesh Eulerian code. The effects on the flow before and after reshock are examined and the results are compared with experimental images of the curtain's evolution. Also a sub-grid mix model in RAGE is applied to the simulations and the computed density and velocity correlations are compared with data available from the experiment. [Preview Abstract] |
Monday, November 24, 2008 4:27PM - 4:40PM |
LD.00005: Hybrid WENO/Central Difference Navier-Stokes Simulation of Reshocked Richtmyer-Meshkov Instability Oleg Schilling, Wai Sun Don A new hybrid WENO/central finite-difference method has been developed for the high-resolution, multi-dimensional, efficient simulation of turbulent mixing induced by interfacial hydrodynamic instabilities. Multi-resolution analysis is used to dynamically determine regions in which large gradients or discontinuities exist (where upwinding is applied) and regions in which the flow is smooth (where central differencing is applied). This method is used to solve the dissipative fluid dynamics equations describing reshocked Richtmyer--Meshkov unstable flow in the Mach $1.3$ Jacobs--Krivets and Mach $1.5$ Vetter--Sturtevant shock tube experiments. The mixing layer widths are shown to be in good agreement with experimental data on the growth of the layer. Additional quantities not measured in the experiment, such as local and global molecular mixing parameters, energy spectra, and statistics are also calculated and compared (when possible) to previously obtained results using monotone-integrated large- eddy simulation and implicit large-eddy simulation methods. [Preview Abstract] |
Monday, November 24, 2008 4:40PM - 4:53PM |
LD.00006: Richtmyer-Meshkov Instabilities with Shocks, Reshocks, and Rarefactions Karnig Mikaelian We point out a variety of experiments that can be carried out at a National Shock Tube Facility to study Richtmyer-Meshkov instabilities generated by reshocks and rarefactions. The rarefactions may be isolated, preceded by a shock, or followed by a shock. Numerical simulations with CALE will be presented and compared with a generalization of the nonlinear Layzer model that includes time-dependent densities. [Preview Abstract] |
Monday, November 24, 2008 4:53PM - 5:06PM |
LD.00007: Richtmyer-Meshkov Experiments on a Reshocked, Low Atwood Number Interface Chris Weber, Nicholas Haehn, Jason Oakley, Mark Anderson, Riccardo Bonazza Low Atwood number (A = ($\rho _{2}$--$\rho _{1})$/($\rho _{2}+\rho _{1})$ = 0.29) Richtmyer-Meshkov instability (RMI) experiments are presented for a near single mode, sinusoidal interface accelerated by an incident and a reflected shock wave. The interface is created by flowing a 50-50{\%} mixture of He+Ar from above and pure Ar from below. Slots at the interface location allow for a stagnation plane to form. A pair of pistons embedded in the shock tube walls force a near sinusoidal, linear ($\eta $/$\lambda $ = 0.01), standing wave, which is accelerated by a $M$ = 1.3 planar shock wave. The setup at the Wisconsin Shock Tube Laboratory allows for the interface development to be observed for a long period ($\sim $8 ms) after the interface is reshocked by the shock wave reflecting off the end wall and before the expansion wave reflected from the driver section end wall reaches the interface. The interface is visualized with planar Mie scattering. The additional vorticity deposited on the interface during reshock causes the spike and bubble to invert phase and grow at a substantially higher rate than before reshock. The experimental results are compared to numerical simulations using the Eulerian AMR code \textit{Raptor} (LLNL). [Preview Abstract] |
Monday, November 24, 2008 5:06PM - 5:19PM |
LD.00008: Experimental investigation of a twice-shocked spherical gas inhomogeneity Nicholas Haehn, Chris Weber, Jason Oakley, Mark Anderson, Riccardo Bonazza Results are presented from a series of experiments and simulations studying the behavior of a spherical gas inhomogeneity impulsively accelerated by an incident and a reflected shock wave. Two Atwood numbers are studied using soap film to create argon and sulfur-hexafluoride bubbles impacted by a planar shock wave of strength $M $= 1.33. The experiments are performed in a 9.2-m-long vertical shock tube with a square internal cross-section, 25.4 cm per side. The bubbles are released from an injector that is pneumatically retracted into the side of the shock tube. For the scenario involving an Argon bubble free falling in ambient nitrogen (A = 0.176), the reshock occurs during the tail end of the bubble's compression regime after it has already shown slight growth and vortex core development. For the SF6 bubble free falling in ambient nitrogen (A = 0.681), the reshock occurs later in the bubble's developmental stage. The flow is visualized with planar Mie scattering and temporal evolutions are analyzed for the spatial dimensions, growth rates and vorticity estimates. PIV analysis is performed for several instances using the soap film as tracer particles. These trends are compared to simulations performed with the Eulerian AMR hydrodynamics code \textit{Raptor }from LLNL. [Preview Abstract] |
Monday, November 24, 2008 5:19PM - 5:32PM |
LD.00009: Interaction between gas cylinder seeded with droplets and an oblique shock Evan Johnson, Mario Chavez, C. Randall Truman, Peter Vorobieff The problem of a planar shock interaction with gas curtains (cylinders) whose plane (axis) of symmetry is parallel to the plane of the shock has been well studied both experimentally and numerically, and in this case, the flow evolution driven by Richtmyer-Meshkov instability is well characterized. However, for a similar \emph{oblique} interaction, with the plane of the shock and the plane (axis) of the density interface being non-parallel, presently only numerical results exist. This problem, however, would be quite interesting to study experimentally both because of a variety of relevant applications and because oblique shock interaction adds large-scale three-dimensionality to the initial conditions. Here we report on the progress of our work on the development of a tiltable Mach 3 shock tube designed specifically to produce such oblique shock interactions and equipped with diagnostics suitable for studies of three-phase flow (light gas, heavy gas, and particles/droplets). The presence of the droplets (or particles) introduces several additional interesting issues here, including the possible effect of shock focusing on the non-gaseous phase carried by the flow. [Preview Abstract] |
Monday, November 24, 2008 5:32PM - 5:45PM |
LD.00010: A detailed numerical investigation of the single-mode Richtmyer-Meshkov instability Amol Dhotre, Praveen Ramaprabhu, Guy Dimonte The single-mode shock-driven Richtmyer-Meshkov (RM) instability is investigated using high resolution numerical simulations.\footnote{Numerical study of the single-mode Richtmyer-Meshkov instability for a comprehensive set of conditions, A. Dhotre, P. Ramaprabhu \& Guy Dimonte, To be submitted to Physics of Fluids.} The growth rate of an initially sinusoidal perturbation is evaluated against linear theory and an impulsive model over a wide range of influential parameters: [A, Ma, 2D/3D, $\gamma$$_{1}/$\gamma$$_{2}$, ka$_{0}$]. The results are in good agreement with linear theory for small amplitudes, and with the impulsive model when compressibility effects may be ignored. For large density differences, spikes exhibit acceleration above the velocity predicted by linear theory, while bubbles decay from the start. The spike acceleration disappears with larger initial amplitudes consistent with simple potential-flow models.\footnote{Modeling of the single-mode Richtmyer-Meshkov instability for a comprehensive set of conditions, Guy Dimonte, P. Ramaprabhu \& A. Velikovich, To be submitted to Physics of Fluids.} Our results present a consistent but complicated picture of the early-stage growth of both small and large amplitude RM, and clarify the regimes of validity in parameter space of several existing linear and nonlinear theories. [Preview Abstract] |
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