The DS2G program is a general program for the computation of two-dimensional or axially symmetric flows by the direct simulation Monte Carlo (DSMC) method. The sampling of the flows may be either for a permanently unsteady flow (with or without ensemble averaging) or for a time averaged steady flow at large times. It is a self-contained executable program for Intel based (486DX or higher) PC's. The data input is through a series of on-screen menus. The output can be through text files and/or files for the TECPLOT post-processing program.

A self-extracting ZIP file to produce the file DS2G.EXE can be downloaded (470kb) as


The data files for the demonstration cases may be downloaded (20 kb) as the self-extracting ZIP file


The user manual for Version 3.2 can be downloaded (748 kb) as


  • Version 1.0 of this program was released in February 1995. Its capabilities were generally similar to the earlier G2 programs, although it allowed in-plane moving surfaces in two-dimensional flows and spinning surfaces in axially symmetric flows.
  • Version 1.1 allowed surfaces to be catalytic for recombination reactions, the circmferential surface velocity could be specified as an angular velocity, and molecules that were lost through round-off error were balanced by the duplication of a nearby molecule.
  • Version 2 introduced a new and faster logic for the molecule moves, together with consequential changes.
  • Version 2.1 (January 1996) allowed different initial conditions in each flow region. This increased the range of unsteady flow problems that can be simulated by the program. In addition, the flux of molecules between regions was sampled.
  • Version 2.2 (May 1996) includes a three-dimensional plot option for the TECPLOT output for steady axially symmetric flows. The text output file has been split into separate files.
  • Version 2.3 (December 1996) allows displacement of interfaces for the setting of periodic boundaries, introduces power-law options for the setting of surface and specified input boundary properties, and allows the molecules from one case to be used as the initial state of a new case.
  • Version 3.0 (March 1998) replaces fixed sub-cells by adaptive transient sub-cells that are defined one cell at a time and are called only from the collision subroutine. For the first demonstration case, the mean spacing between collision pairs is reduced by 60%, the execution time is reduced by 15%, and the storage required by the cell structure has been more than halved. This is particularly useful for unsteady flow calculations without ensemble averaging and the program has been modified to facilitate these calculations. The downloadable program is now restricted to 200,000 simulated molecules, but an unrestricted version is available to registered users (application via e-mail).
  • Version 3.1 (August 1998) adds diagnostic output to the TECPLOT file that indicates whether the DSMC criteria have been met. The number of molecules in not restricted, but I would like to hear from new users.
  • Version 3.2 (June 1999) adds an adiabatic diffuse (zero heat transfer) option to the surface properties. This is activated by setting a surface temperature to -2. (specular reflection now requires -1.). The surface recovery temperature is output in a new column in DS2GS.TXT.

In addition, program bugs have been progressively corrected.The current file is dated 13 June, 1999

The purpose of the programs is to demonstrate the DSMC method. They are nor guaranteed to be free of error and should not be relied upon for solving problems where an error could result in injury or loss. If the programs are used for such solutions, it is entirely at the user's risk.

Further enquiries should be addressed to Graeme Bird at [email protected]