DNS of the thermal effects of laser energy deposition in isotropic turbulence

Shankar Ghosh, Krishnan Mahesh

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Abstract

The interaction of a laser-induced plasma with isotropic turbulence is studied using numerical simulations. The simulations use air as the working fluid and assume local thermodynamic equilibrium. The numerical method is fully spectral and uses a shock-capturing scheme in a corrector step. A model problem involving the effect of energy deposition on an isolated vortex is studied as a first step towards plasma/turbulence interaction. Turbulent Reynolds number R = 30 and fluctuation Mach numbers Mt = 0.001 and 0.3 are considered. A tear-drop-shaped shock wave is observed to propagate into the background, and progressively become spherical in time. The turbulence experiences strong compression due to the shock wave and strong expansion in the core. This behaviour is spatially inhomogeneous and non-stationary in time. Statistics are computed as functions of radial distance from the plasma axis and angular distance across the surface of the shock wave. For Mt = 0.001, the shock wave propagates on a much faster time scale compared to the turbulence evolution. At Mt of 0.3, the time scale of the shock wave is comparable to that of the background. For both cases the mean flow is classified into shock formation, shock propagation and subsequent collapse of the plasma core, and the effect of turbulence on each of these phases is studied in detail. The effect of mean vorticity production on the turbulent vorticity field is also discussed. Turbulent kinetic energy budgets are presented to explain the mechanism underlying the transfer of energy between the mean flow and background turbulence.

Original languageEnglish (US)
Pages (from-to)387-416
Number of pages30
JournalJournal of Fluid Mechanics
Volume654
DOIs
StatePublished - Jul 2010

Bibliographical note

Funding Information:
This work is supported by the United States Air Force Office of Scientific Research under grant FA9550-04-1-0341 and FA-9550-04-1-0064. Computing resources were provided by the Minnesota Supercomputing Institute, the San Diego Supercomputing centre and the National centre for Supercomputing Applications.

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