Recommended direct simulation Monte Carlo collision model parameters for planetary entry and related applications

Direct simulation Monte Carlo (DSMC) is an essential tool in the modeling of spacecraft atmospheric entry. The accuracy of transport processes in DSMC simulations depends on the collision cross section parameters used to model the particle interactions. In this work, we provide a comprehensive collision-specific Variable Soft Sphere (VSS) parameter database for accurate simulation of transport properties in DSMC. A Nelder–Mead optimization scheme is used to find optimized VSS parameters from collision integrals, which are acquired either from high-fidelity literature sources or computed herein using a phenomenological potential model. The final collision parameter database contains over 200 neutral and ionized species, encompassing the compositions of all planetary atmospheres in the solar system, as well as the ablation and pyrolysis products of common spacecraft thermal protection systems. Best-fit parameters are provided over a range of 1000–20 000 K. A secondary database, fitted from 300 to 4000 K, is provided for use in other applications, such as plume impingement, porous media flow, or combustion phenomena. The accuracy of the database is evaluated by comparing gas transport properties predicted by the database with those obtained from the ab initio collision integral data. The average error across the high and low temperature-range databases was found to be less than 1% and 3%, respectively. The provided parameter sets can be readily applied to model any neutral or weakly ionized gas mixture containing the included species, thus, providing a comprehensive database that will be of great interest to the DSMC community.