Development and application of particle methods at DLR Spacecraft department

Abstract

The Spacecraft department in the DLR Institute for Aerodynamics and Flow Technology conducts research and development on a wide array of spacecraft aerothermodynamic problems. It operates large-scale test facilities for high-enthalpy hypersonic flows and high-vacuum plume test facilities for chemical and electric orbital propulsion. The experimental capabilities are complemented by high-fidelity in-house Navier-Stokes solvers "TAU" and "CODA", as long as the associated flow problems are characterized by sufficiently low Knudsen number. Driven by the need to study more rarefied flows with high computational efficiency on an engineering-scale, we rely on the Direct Simulation Monte Carlo (DSMC) code SPARTA, developed at Sandia National Laboratories. A number of technically relevant flow scenarios involve domains of both high and low Knudsen number. While the DSMC method correctly models gas flows with low Knudsen number, it is attractive to hybridize it with a numerical scheme that computes these flows more efficiently. The particle-based Fokker-Planck method appears to be a natural choice, as it essentially only replaces the collision step in DSMC with an alternate scheme of momentum and energy redistribution that does not rely on evaluating binary collisions. In this talk, we present an overview of recent developments, extensions, and applications of the particle-based Fokker-Planck method carried out at DLR Goettingen. The original method has been extended to model gas mixtures, internal energy redistribution in diatomic and polyatomic species, and recently also gas-phase chemical reactions, while maintaining compatibility with models customarily used in DSMC. We show application examples in which the Fokker-Planck solutions are compared with those of DSMC and Navier-Stokes, and discuss the need for further development.