Unstructured continuum-kinetic solver with fluid-particle interaction for in-space propulsion contaminant dispersal

A new parallel generalized unstructured grid solver for prediction of rarefied gas dynamics is presented. The method is based on the direct numerical solution of the semi-classical Boltzmann equation using a discrete velocity method (DVM) and supports accurate prediction of non-continuum flows in near-vacuum rarefied flow regimes. For in-space propulsion applications which involve mixed continuum-rarefied environments, the flow regimes are solved separately through the use of DVM and hybrid RANS/LES solution procedures, respectively, on the same computational domain while interacting with one another. The solver also supports coupled Lagrangian particle transport and coalescence/breakup modeling to enable prediction of plume flow impingement and contaminant dispersal through mixed continuum-rarefied environments around spacecraft. Such simulation capabilities are essential for the prediction of spacecraft environments concerning plume impingement pressure, heating, and contamination on spacecraft components such as solar panels and sensitive instruments. Example applications include venting and plume flow environments from spacecraft main engines and attitude control thrusters firing in near-vacuum conditions. The framework upon which the solvers are developed is introduced along with a detailed description of the direct Boltzmann solution and collision integral evaluation procedures. The accuracy of standalone kinetic and coupled continuum-kinetic predictions is validated by comparison against experimental data for shock structure using various different intermolecular interaction models. Results are presented to demonstrate the merits of the capability for prediction of high-speed gas-particle interaction through complex moving shock systems, and thruster plume flow impingement with liquid droplet tracking in near-vacuum conditions.