Thomas E. Schwartzentruber

University of Michigan

Title: Particle Simulation for the Multi-Scale Modeling of Gas Flows

Abstract:

As aerospace vehicles continue to fly higher and faster, and as manufacturing technology continues to reduce the size of engineering devices below the micrometer level, accurate numerical simulation begins to require the resolution of flow scales ranging from continuum to free-molecular. When the characteristic length scales of shock waves, boundary layers, sharp leading edges, and micro-electromechanical systems approach the distance traveled by gas particles between collisions, the assumption implicit in the continuum Navier-Stokes equations of collisional near-equilibrium breaks down. Although particle methods are able to accurately simulate such highly non-equilibrium regions, they become computationally prohibitive in regions of continuum flow.

A hybrid particle-continuum numerical method designed for hypersonic non-equilibrium flows is presented. The method utilizes the direct simulation Monte Carlo (DSMC) method in regions of non-equilibrium and solves the continuum Navier-Stokes equations in regions of near-equilibrium. The hybrid numerical algorithm loosely couples particle and continuum regions in order to efficiently resolve the disparate length and time scales encountered in hypersonic flows. Results are presented for normal shock waves and blunt body flows where the hybrid method is able to reproduce full DSMC flow field and surface properties in less time, using less memory. The speedup achieved is directly proportional to the relative size of the continuum regions. For multi-scale hypersonic flows where highly localized regions of non-equilibrium are imbedded within a mostly continuum flow, the hybrid method is shown to result in significant computational savings compared with full particle simulation.