Laboratory Astrophysics

 

Testing Astrophysics in the Lab: Simulations with the FLASH code


Dwarkadas, Vikram


(ASCI FLASH Center, University of Chicago)


American Physical Society, 45th Annual Meeting of the Division of Plasma Physics, October 27-31, 2003, Albuquerque, New Mexico, MEETING ID: DPP03, abstract #GM1.002



10/2003


2003APS..DPPGM1002D

Abstract

FLASH is a multi-physics, block-structured adaptive mesh refinement code for studying compressible, reactive flows in various astrophysical environments. We compare the results of two- and three-dimensional FLASH simulations to experimental data obtained at Los Alamos National Laboratory (LANL). The LANL experiment (Tomkins et al. 2003, PhFl, 15, 896) involves the lateral interaction between a planar Ma=1.2 shock wave with one or two cylinders of sulphur hexafluoride (SF6) gas. The development of primary and secondary flow instabilities after the passage of the shock, as observed in the experiments and numerical simulations, are reviewed and compared. We investigate the deposition of vorticity due to the impact of the shock wave on the cylinder, and the transition from laminar to turbulent flow. The interaction of shock waves with high-density clouds is a common phenomenon in astrophysics. Shock-cloud interactions are seen in the interstellar medium and within supernova remnants and wind-driven nebulae. On large scales, refraction of galactic radio jets flowing past density gradients provides conditions suitable for strong vorticity generation, jet bending, and eventual jet disruption. On smaller scales, interactions between shocks and clouds have been proposed as a means to trigger the collapse of giant molecular clouds, leading to the onset of star formation. By carefully comparing our numerical simulations with experimental data we will validate FLASH for shock-cloud interactions, albeit in the restricted regime of low-Mach number adiabatic planar shocks and for low density contrasts. Following similarity arguments, such comparisons build confidence that the numerical simulations adequately describe the hydrodynamical evolution of shock-cloud interactions on timescales inaccessible to direct observations.

Simulation of Vortex--Dominated Flows Using the FLASH Code


Dwarkadas, Vikram; Plewa, Tomek; Weirs, Greg; Tomkins, Chris; Marr-Lyon, Mark


eprint arXiv:astro-ph/0403109


03/2004


11 pages, to appear in the proceedings of the conference on "Adaptive Mesh Refinement - Theory and Applications", editors Tomasz Plewa, Timur Linde and V. Gregory Weirs


2004astro.ph..3109D

Abstract

We compare the results of two--dimensional simulations to experimental data obtained at Los Alamos National Laboratory in order to validate the FLASH code. FLASH is a multi--physics, block--structured adaptive mesh refinement code for studying compressible, reactive flows in various astrophysical environments. The experiment involves the lateral interaction between a planar Ma=1.2 shock wave with a cylinder of gaseous sulfur hexafluoride (SF$_6$) in air. The development of primary and secondary flow instabilities after the passage of the shock, as observed in the experiments and numerical simulations, are reviewed and compared. The sensitivity of numerical results to several simulation parameters are examined. Computed and experimentally measured velocity fields are compared. Motivation for experimental data in planes parallel to the cylinder axis is provided by a speculative three--dimensional simulation.

Validating the Flash Code: Vortex-Dominated Flows


Weirs, Greg; Dwarkadas, Vikram; Plewa, Tomek; Tomkins, Chris; Marr-Lyon, Mark


AA(ASCI FLASH Center, University of Chicago), AB(ASCI FLASH Center, University of Chicago), AC(ASCI FLASH Center, University of Chicago), AD(Los Alamos National Laboratory), AE(Los Alamos National Laboratory)


Astrophysics and Space Science, Volume 298, Issue 1-2, pp. 341-346   07/2005


2005Ap&SS.298..341W

Abstract

As a component of the Flash Center’s validation program, we compare FLASH simulation results with experimental results from Los Alamos National Laboratory. The flow of interest involves the lateral interaction between a planar M a = 1.2 shock wave with a cylinder of gaseous sulfur hexafluoride (SF6) in air, and in particular the development of primary and secondary instabilities after the passage of the shock. While the overall evolution of the flow is comparable in the simulations and experiments, small-scale features are difficult to match. We focus on the sensitivity of numerical results to simulation parameters.

Progress toward Kelvin-Helmholtz instabilities in a High-Energy-Density Plasma on the Nike laser


Harding, E. C.; Drake, R. P.; Gillespie, R. S.; Grosskopf, M. J.; Huntington, C. M.; Aglitskiy, Y.; Weaver, J. L.; Velikovich, A. L.; Plewa, T.; Dwarkadas, V. V.


American Physical Society, 2008 APS April Meeting and HEDP/HEDLA Meeting, April 11-15, 2008, abstract #8HE.004


04/2008


2008APS..APR8HE004H

Abstract

In the realm of high-energy-density (HED) plasmas, there exist three primary hydrodynamic instabilities of concern: Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH). Although the RT and the RM instabilities have been readily observed and diagnosed in the laboratory, the KH instability remains relatively unexplored in HED plasmas. Unlike the RT and RM instabilities, the KH instability is driven by a lifting force generated by a strong velocity gradient in a stratified fluid. Understanding the KH instability mechanism in HED plasmas will provide essential insight into oblique shock systems, jets, mass stripping, and detailed RT-spike development. In addition, our KH experiment will help provide the groundwork for future transition to turbulence experiments. We present 2D FLASH simulations and experimental data from our initial attempts to create a pure KH system using the Nike laser at the Naval Research Laboratory.

Progress Toward Kelvin-Helmholtz instabilities in a High-Energy-Density Plasma on the Nike Laser


Harding, E. C.; Drake, R. P.; Aglitskiy, Y.; Dwarkadas, V. V.; Gillespie, R. S.; Grosskopf, M. J.; Huntington, C. M.; Gjeci, N.; Campbell, D. A.; Marion, D. C.


American Physical Society, 49th Annual Meeting of the Division of Plasma Physics, November 12-16, 2007, abstract #NP8.041


11/2007


2007APS..DPPNP8041H

Abstract

In the realm of high-energy-density (HED) plasmas, there exist three primary hydrodynamic instabilities: Rayleigh-Taylor (RT), Richtmyer-Meshkov (RM), and Kelvin-Helmholtz (KH). Although the RT and the RM instabilities have been observed in the laboratory, no experiment to our knowledge has cleanly diagnosed the KH instability. While the RT instability results from the acceleration of a more dense fluid into a less dense fluid and the RM instability is due to shock deposited vorticity onto an interface, the KH instability is driven by a lifting force generated by velocity shear at a perturbed fluid interface. Understanding the KH instability mechanism in HED plasmas will provide essential insight into detailed RT-spike development, mass stripping, many astrophysical processes, as well as laying the groundwork for future transition to turbulence experiments. We present 2D simulations and data from our initial attempts to create a pure KH system using the Nike laser at the