arXiv subjects

Christopher Flint

Publications and source records attributed to Christopher Flint.

4 recordsLinked to original sources

arXiv2017

A Partial Entropic Stabilization of Lattice Boltzmann MHD

The entropic lattice Boltzmann algorithm of Karlin et. al. is partially extended to magnetohydrodynamics, based on the Dellar model of introducing a vector distribution for the magnetic field. This entropic ansatz is now applied only to the scalar particle distribution function so as to permit the many problems entailing magnetic field reversal. A 9-bit lattice is employed for both particle and magnetic distributions for our two dimensional simulations. The entropic ansatz is benchmarked against our earlier multiple relaxation lattice-Boltzmann model for the Kelvin-Helmholtz instability in a magnetized jet. Other two dimensional simulations are performed and compared to results determined by more standard direct algorithms: in particular the switch over between the Kelvin-Helmholtz/tearing mode instability of Chen et. al., and the generalized Orszag-Tang vortex model of Biskamp-Welter. Very good results are achieved.

physics.plasm-ph↗

arXiv2017

A large eddy lattice Boltzmann simulation of magnetohydrodynamic turbulence

Large eddy simulations (LES) of a lattice Boltzmann magnetohydrodynamic (LB-MHD) model are performed for the unstable magnetized Kelvin-Helmholtz jet instability. This algorithm is an extension of Ansumali et. al. (2004) to MHD in which one performs first an expansion in the filter width on the kinetic equations followed by the usual low Knudsen number expansion. These two perturbation operations do not commute. Closure is achieved by invoking the physical constraint that subgrid effects occur at transport time scales. The simulations are in very good agreement with direct numerical simulations.

physics.plasm-ph↗

arXiv2017

A Partial Entropic Lattice Boltzmann MHD Simulation of the Orszag-Tang Vortex

Karlin has introduced an analytically-determined entropic lattice Boltzmann algorithm for Navier-Stokes turbulence. Here this is partially extended to a lattice Boltzmann model of magnetohydrodynamics, on using the vector distribution function approach of Dellar for the magnetic field. (which is permitted to have field reversal). The partial entropic algorithm is benchmarked successfully against standard simulations of the Orszag-Tang vortex (1979).

physics.plasm-ph↗

arXiv2016

Lattice Boltzmann Large Eddy Simulation Model of MHD

The work of Ansumali \textit{et al.}\cite{Ansumali} is extended to Two Dimensional Magnetohydrodynamic (MHD) turbulence in which energy is cascaded to small spatial scales and thus requires subgrid modeling. Applying large eddy simulation (LES) modeling of the macroscopic fluid equations results in the need to apply ad-hoc closure schemes. LES is applied to a suitable mesoscopic lattice Boltzmann representation from which one can recover the MHD equations in the long wavelength, long time scale Chapman-Enskog limit (i.e., the Knudsen limit). Thus on first performing filter width expansions on the lattice Boltzmann equations followed by the standard small Knudsen expansion on the filtered lattice Boltzmann system results in a closed set of MHD turbulence equations provided we enforce the physical constraint that the subgrid effects first enter the dynamics at the transport time scales. In particular, a multi-time relaxation collision operator is considered for the density distribution function and a single relaxation collision operator for the vector magnetic distribution function. The LES does not destroy the property that $\nabla \cdot \mathbf B = 0$ automatically without the need for divergence cleaning.

physics.plasm-ph↗