Till Frieler

For the numerical description of rarefied gas flows, which for example occur in arc jet thrusters under vacuum conditions, direct simulation methods such as DSMC (Direct Simulation Monte Carlo) are commonly used. To validate experiments carried out under these conditions the ZARMdsmcFoam solver is being developed.

Based on the standard implementation dsmcFoam in the open source software bundle OpenFOAM, the new solver ZARMdsmcFoam offers some additional features and changes. These changes include the implementation of a new inlet-model called ZARMInOutflow that allows the direct specification of mass or volume flows over the inflow edges of the volume. Mass and volume flows can be measured well in experiment and therefore are a good boundary condition for numerical simulations. With the new inlet-model the user now can define a “numberDensities”, which is equal to the, per area and second initialized, number of molecules.

The second major change had been made to the “trackToFace”- method in the standard implementation of dsmcFoam. In order to actually define an effective mass or volume flow over the edges of the inlet patch area, test molecules which hit an open border with the name “inlet” are no longer deleted but reflected. This creates a steady flow of molecules over the edges of the inlet without mass escaping from the system through these areas.

Due to the high pressure differences within the simulation volume further changes had to be made to the code to handle particle collisions in high pressure regions. Therefore an collision limiter method was implemented, limiting the number to two collisions per particle per timestep.