Stochastic Particle Method for
Rarefied Gas Flows

A Multiphysics Coupled DSMC Simulation Framework

Rarefied and high-altitude gas flows often involve complex physical phenomena—such as nonequilibrium chemistry, gas–surface interactions, radiation, and plasma effects—that require a particle-based description beyond continuum models. The Direct Simulation Monte Carlo (DSMC) method provides a stochastic particle framework that captures intermolecular collisions and rarefied transport phenomena across all Knudsen regimes. As aerospace systems become more advanced, multiphysics coupled simulations are increasingly essential for reliable prediction and design.

• Chemical Reactions: dissociation, ionization, recombination, and surface recombination

• Energy Exchange: translational–rotational–vibrational (trn–rot–vib) coupling, quantized vibrational modes

• Gas–Surface Interactions: catalytic effects, absorption, deposition, and ablation

• Radiation Transport: particle-based photon Monte Carlo (PMC) solvers coupled with DSMC

• Plasma Effects: particle-in-cell (PIC) methods for electromagnetic field coupling

• Multiphase Coupling: gas–liquid–solid interactions for plume–dust or ablation modeling

This multiphysics DSMC framework allows accurate simulations of hypersonic reentry vehicles, electric propulsion systems, and planetary entry missions, where rarefaction and nonequilibrium effects dominate. By advancing new collision models, improving transport coefficients, and coupling with radiation/plasma solvers, our approach provides a versatile platform for high-fidelity prediction of rarefied aerothermodynamics.

New Kinetic Models for Hypersonic Rarefied Gas Flows

Accurate prediction of hypersonic rarefied gas flows requires kinetic modeling beyond the continuum and Navier–Stokes descriptions. The Boltzmann equation provides the fundamental framework for describing molecular transport and nonequilibrium effects, but its high-dimensional nature makes direct solutions computationally prohibitive. To address this challenge, we develop new reduced-order kinetic models—based on Fokker–Planck and Bhatnagar–Gross–Krook (BGK) formulations—that retain essential physical fidelity while enabling efficient simulation of nonequilibrium gas dynamics.

• BGK-Type Collision Models: Simplified relaxation operators preserving conservation laws and correct Prandtl numbers for high-temperature gases.

• Fokker–Planck Formulation: Continuous stochastic representation of collisional diffusion in velocity space, suitable for near-continuum rarefied regimes.

• Multi-Temperature Extensions: Separate translational, rotational, and vibrational energy exchange for diatomic and polyatomic gases.

• Reactive Kinetics Integration: Coupling with chemical nonequilibrium processes such as dissociation and ionization.

• Boundary Conditions: Gas–surface interaction models incorporating accommodation, reflection, and catalytic effects.

By bridging Boltzmann-based accuracy and continuum-level efficiency, these new kinetic models provide a unified framework for simulating hypersonic reentry flows, high-altitude aerothermodynamics, and rarefied propulsion plumes.