Hybrid Particle-Continuum Simulations of Nonequilibrium Hypersonic Blunt-Body Flowfields

Abstract

A modular particle-continuum (MPC) numerical method is presented which solves the Navier-Stokes (NS) equations in regions of near-equilibrium and uses the direct simulation Monte Carlo (DSMC) method where the flow is in non-equilibrium. The MPC method is designed specifically for steady-state, hypersonic, nonequilibrium flows and couples existing, state-of-the-art DSMC and NS solvers into a single modular code. The MPC method is tested for 2D flow of N 2 at various Mach numbers over a cylinder where the global Knudsen number is 0.01. For these conditions, NS simulations significantly over-predict the local shear-stress, and also over-predict the peak heating rate by 5-10% when compared with full DSMC simulations. DSMC also predicts faster wake closure and 10-15% higher temperatures in the immediate wake region. The MPC code is able to accurately reproduce DSMC flow field results, local velocity distributions, and surface properties up to 2.8 times faster than full DSMC simulations. The computational time saved by the MPC method is directly proportional to the fraction of the flow field which is in near-equilibrium. It is found that particle simulation of the shock interior is not necessary for accurate prediction of surface properties, however particle simulation of the boundary layer and near-wake region is.

Hybrid Particle-Continuum Simulations of Hypersonic Flow Over a Hollow-Cylinder-Flare Geometry

“…Previous research focusing on 1-D normal shock waves [12] and hypersonic flow over a 2-D cylinder [11,13] demonstrated the accuracy of the MPC method for computing flowfield data, velocity distributions, and surface properties. The hypersonic interaction flow studied in this paper provides a significant challenge for the MPC algorithm, compared with the previous MPC research.…”

“…Cells in which Kn GL > Br cutoff are labeled as DSMC cells and the remainder are labeled as NS cells, thus defining an interface between the two regions. Previous studies have recommended [31] and validated [11][12][13] a cutoff value of Br cutoff 0:05. A slightly more conservative value of Br cutoff 0:03 is used for the MPC simulations presented in this paper.…”

“…In this study, the modular particle-continuum (MPC) algorithm [11] is used to simulate a steady-state hypersonic interaction flow. The MPC method was initially developed and tested for 1-D normal shock waves [12] as well as for hypersonic flow over a 2-D-cylinder geometry [13]. The MPC algorithm loosely couples DSMC and NS regions, which have different mesh densities and are updated using different time steps.…”

“…Such an approach enables both spatial-and temporal-scale decoupling while lending itself to a modular implementation [14], which uses existing state-of-the-art DSMC and NS codes (unmodified) within the hybrid code. For flow over a 2-D cylinder, the MPC method has been shown to reproduce the flowfields, surface properties, and local velocity distributions predicted by full DSMC simulations 1.4 to 3.3 times faster while requiring less memory [13,14].…”

A Two-Temperature Open-Source CFD Model for Hypersonic Reacting Flows, Part Two: Multi-Dimensional Analysis

“…where λ is the local mean free path of the gas molecules and φ can either be the gas density, the temperature, or the magnitude of the velocity vector |U| (or max (|U|, a) in the denominator, where a is the speed of sound for low-speed regions [34]). The degree of local continuum breakdown is then evaluated as the maximum for all of the aforementioned flow quantities…”