uniGasFoam: a particle-based OpenFOAM solver for multiscale rarefied gas flows

TL;DR

uniGasFoam is an open-source, particle-based solver integrated with OpenFOAM for efficient multiscale rarefied gas flow simulations, combining DSMC and stochastic particle methods with adaptive algorithms for improved robustness and scalability.

Contribution

The paper introduces uniGasFoam, a novel hybrid particle-based solver that simplifies coupling, enhances efficiency, and is adaptable for various rarefied gas flow simulations within the OpenFOAM framework.

Findings

Excellent agreement with benchmark cases.

Significant computational speedups over pure DSMC.

Robustness and scalability improvements.

Abstract

This paper presents uniGasFoam, an open-source particle-based solver for multiscale rarefied gas flow simulations, which has been developed within the well-established OpenFOAM framework, and is an extension of the direct simulation Monte Carlo (DSMC) solver dsmcFoam+. The developed solver addresses the coupling challenges inherent in hybrid continuum-particle methods, originating from the disparate nature of finite-volume (FV) solvers found in computational fluid dynamics (CFD) software and DSMC particle solvers. This is achieved by employing alternative stochastic particle methods, resembling DSMC, to tackle the continuum limit. The uniGasFoam particle-particle coupling produces a numerical implementation that is simpler and more robust, faster in many steady-state flows, and more scalable for transient flows compared to conventional continuum-particle coupling. The presented framework is unified and generic, and can couple DSMC with stochastic particle (SP) and unified stochastic particle (USP) methods, or be employed for pure DSMC, SP, and USP gas simulations. To enhance user experience, optimise computational resources and minimise user error, advanced adaptive algorithms such as transient adaptive sub-cells, non-uniform cell weighting, and adaptive global time stepping have been integrated into uniGasFoam. In this paper, the hybrid USP-DSMC module of uniGasFoam is rigorously validated through multiple benchmark cases, consistently showing excellent agreement with pure DSMC, hybrid CFD-DSMC, and literature results. Notably, uniGasFoam achieves significant computational gains compared to pure dsmcFoam+ simulations, rendering it a robust computational tool well-suited for addressing multiscale rarefied gas flows of engineering importance.