Direct Simulation Monte Carlo for astrophysical flows - I. Motivation and methodology
Abstract
We describe a hybrid Direct Simulation Monte Carlo (DSMC) code for simultaneously solving the collisional Boltzmann equation for gas and the collisional Boltzmann equation for stars and dark matter for problems important to galaxy evolution. This project is motivated by the need to understand the controlling dynamics at interfaces between gases of widely differing densities and temperature, i.e. multiphase media. While more expensive than hydrodynamics, the kinetic approach does not suffer from discontinuities and it applies when the continuum limit does not, such as in the collapse of galaxy clusters and at the interface between coronal halo gas and a thin neutral gas layer. Finally, the momentum flux is carried, self-consistently, by particles and this approach explicitly resolves and thereby `captures' shocks. The DSMC method splits the solution into two pieces: (1) the evolution of the phase-space flow without collisions and (2) the evolution governed the collision term alone without phase-space flow. This splitting approach makes DSMC an ideal match to existing particle-based N-BODY codes. If the mean-free path becomes very small compared to any scale of interest, the method abandons simulated particle collisions and simply adopts the relaxed solution in each interaction cell consistent with the overall energy and momentum fluxes. This is functionally equivalent to solving the Navier-Stokes equations on a mesh. Our implementation is tested using the Sod shock-tube problem and the non-linear development of a Kelvin-Helmholtz unstable shear layer.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2014
- DOI:
- 10.1093/mnras/stt2406
- arXiv:
- arXiv:1304.3941
- Bibcode:
- 2014MNRAS.438.2995W
- Keywords:
-
- atomic processes;
- hydrodynamics;
- methods: numerical;
- ISM: evolution;
- ISM: structure;
- galaxies: ISM;
- Astrophysics - Instrumentation and Methods for Astrophysics;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 13 pages, 4 figures, submitted to MNRAS, revised figures, corrected typos, and incorporated comments