Development and validation studies of a multi-purpose DSMC code

Abstract

A parallel direct simulation Monte Carlo (DSMC) solver has been developed to ultimately couple with an existing granular code in order to model positioning-rocket plume expansion in the lunar atmosphere and its interaction with the regolith. The challenge is to develop of a multi-species DSMC efficient model and code to fit the target problem. This model and code are here described and results from the model are compared for validation and verification purposes either with existing experimental data or with similar results from similar simulations of wall-bounded canonical flows. In particular, the modeling of Couette flow with different collision schemes provides an opportunity to select a sufficiently numerically efficient collision model to reduce computational costs. Since the objective of the code is to study expansion flows including the plume species of CO₂, N₂, and H₂O and their interactions with the multi-species composition of the Moon atmosphere (i.e. Ar, He, and Ne), thermal and mass diffusion of mixtures were also studied to show that the code accurately models multispecies situations. To acquire such an ability, the collision and sampling algorithm of the single species code was improved to handle complex multi-species gas interactions. A good agreement with experimental data is achieved, showing that the code accurately predicts the thermal and mass diffusion coefficients of mixtures. Finally, the expanding nature of the plume results in thermochemical nonequilibrium flow, especially in rarefied environments, due to insufficient collision rates. To this end, the rate and the amount of energy transfer among the translational, rotational, and vibrational modes are tested with the previous numerical data and with analytical results.