SPARTA is an acronym for Stochastic PArallel Rarefied-gas Time-accurate Analyzer.

SPARTA is a parallel DSMC or Direct Simulation Monte Carlo code for performing simulations of low-density gases in 2d or 3d. Particles advect through a hierarchical Cartesian grid that overlays the simulation box. The grid is used to group particles by grid cell for purposes of performing collisions and chemistry. Physical objects with triangulated surfaces can be embedded in the grid, creating cut and split grid cells. The grid is also used to efficiently find particle/surface collisions.

SPARTA runs on single processors or in parallel using message-passing techniques and a spatial-decomposition of the simulation domain. The code is designed to be easy to modify or extend with new functionality.

SPARTA is distributed as an open source code under the terms of the GPL, or sometimes (by request) under the terms of the GNU Lesser General Public License (LGPL). The current version can be downloaded here.

SPARTA was primarily developed at Sandia National Laboratories, a US Department of Energy (DOE) laboratory. The authors and funding are listed on this page.

• (9/24) Release of version 4 Sep 2024. It adds create_isurf to convert explicit surfaces to implicit surfaces, custom per-surf options to fix emit/surf, a variable special function which allows particle-style variables to access per-grid quantities, and adds momentum and energy contributions of fix emit/surf in the results of compute surf. See more details here.
• (3/24) Release of version 7 Mar 2024. It adds support for global variable time stepping, enhances functionality of custom attributes for particles, grid cells, and surface elements, adds Kokkos support for FFTs and surface reactions, adds an option to compute chemistry rates without performing reactions, and adds an option to dump the area of surface elements to a file with the dump surf command. See more details here.
• (4/23) Release of version 13 Apr 2023. It includes support for Python 3, a new fix surf/temp command, support for custom per-grid-cell attributes, an optimized particle move algorithm when a model has a regular grid and no surface elements, a new option for the create_particles command to add particles in grid cells cut by surface elements. See more details here.
• (7/22) Release of version 18 July 2022. It includes new options for the compute surf command, a new no-slip option for specular surface collisiont, and a new surface collision adiabatic model with isotropic scattering. See more details here.
• (2/22) Options to add various kinds of external fields to influence particle advection. They can be spatially or time varying and applied on a per-particle or per-grid-cell basis. See the doc page for the global field command.
• (10/21) Added a surf_react adsorb command which has support for on-surface chemistry reactions and storage of surface state, i.e. per-surface-element concentrations of various on-surface species. This enables modeling of both gas/surface and surface/surface chemical reaction networks.
• (11/20) Removed hierarchical grid parent cells from the internally stored data structures. The code now only stores child cells. For large problems with many levels of grid adaptation, this frees up a large amount of memory.
• (1/20) Added support for transparent surfaces which tally statistics when particles pass throught them.
• (10/19) Added these commands for ablation modeling of implicit surface elements: fix ablate, compute isurf/grid, compute react/isurf/grid, write_isurf.
• (4/19) Added support for implicit 2d and 3d surface elements defined by a grid corner point values in a read-in file. These are in contrast to explicit surface elements defined by line segments (2d) or triangles (3d).
• (2/19) Added support for distributed surface elements so that complex surfaces with huge element counts can be modeled, with the elements stored acrossed processors.
• (8/18) SPARTA development is now supported on GitHub and with a mail list.
• (1/18) Added new sections to the Benchmark page with performance results using the new Kokkos accelerator options on a variety of new machines and hardware, including multi-core CPUs (via threading), GPUs, and KNLs.
• (12/17) Added a KOKKOS package to the code to allow building with the open-source Kokkos library which provides support for running SPARTA on different architectures, including multi-core CPUs (via threading), GPUs, and KNLs. See this section of the manual for details.
• (4/17) Added a subsonic pressure boundary condition via a surf_collide piston command, as well as a 2d/3d FFT capability for grid based quantities on regular grids via the compute fft/grid command.
• (8/16) Added fix ave/histo and fix ave/histo/weight commands to enable histogramming of various quantities during a simulation.
• (1/16) Added grid-style variables so that user-defined per-grid quantities can be calculated on-the-fly and output more easily.
• (10/15) Added a near-neighbor collision model for selecting pairs of collision partners.
• (9/15) Posted slides for a half-day tutorial short-course on SPARTA, taught at the biennial DSMC15 conference. See the Tutorials link above.
• (8/15) Added static and on-the-fly grid adaptivity via the adapt_grid and fix adapt commands. Also added commands to move or remove surface elements.
• (5/15) Added a fix emit/surf command to enable particle outflux from surface elements, including their use as a global influx boundary.
• (5/15) Surface reaction models have been added via the surf_react command. The full set of dissociation, ionization, exchange, and recombination reactions, for both gas-phase and surface chemitstry are now implemented.
• (5/15) Added an ambipolar approximation for modeling charged plasmas. See this howto discussion for an explanation of using the various new commands and command options that enable the approximation.
• (2/15) Added a fix emit/face/file command to enable spatially-varying particle influx through a simulation box face, as defined by a file of mesh points and values.
• (12/14) Added two new reaction styles to the react command, for the Quantum-Kinetic (QK) model and a hybrid Total Collision Energy / Quantum Kinetic (TCE/QK) model.
• (10/14) Added two Python scripts which can convert SPARTA output files to ParaView format for interactive 3d viz. Paraview is a popular freely-available visualization tool.
• (8/14) Added a stl2surf.py tool to convert STL-format triangulation files into the SPARTA surface file format.
• (8/14) Enabled axi-symmetric 2d models. See Section 4.2 of the manual for details.
• (7/14) Initial open-source release of SPARTA.

This is work by Michael Gallis (magalli at sandia.gov) at Sandia.

This calculation was done to model Richtmyer/Meshkov mixing which occurs when a light gas is on top of a heavier gas and a shock induces mixing and turbulent effects.

This is a large 2d calculation of He (green) on top of Ar (red). 4.5B particles were run with 400M grid cells for 240K timesteps. The simulation was run on 32K nodes (16 cores per node, 512K MPI tasks) of the Sequoia BG/Q machine at Lawrence Livermore National Labs (LLNL).

Snapshot images of the simulation were created using SPARTA's dump image command, rather than saving particle data to disk. The first 2 images are the initial and final state of the simulation. The rightmost image is a movie of the simulation.

2 images and a 0.5 Mb QuickTime movie

This paper has further details about the mixing model:

Direct Simulation Monte Carlo: The Quest for Speed, M. A. Gallis, J. R. Torczynski, S. J. Plimpton, D. J. Rader, and T. Koehler, Proceedings of the 29th Rarefied Gas Dynamics (RGD) Symposium, Xi'an, China, July 2014. (to be published by AIP) (abstract)