Hybrid Particle-Continuum Simulations of Non-Equilibrium Hypersonic Blunt Body Flow Fields

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.

A hybrid DSMC/Navier–Stokes frame to solve mixed rarefied/nonrarefied hypersonic flows over nano‐plate and micro‐cylinder

“…In this work, we use Kn GLL as the breakdown parameter to determine the continuum–molecular interface. Although Kn GLL has been widely used to determine the continuum breakdown , there are some inherent limitations and approximations in this parameter. In particular, this parameter does not successfully capture the continuum breakdown within the boundary layer .…”

“…The benefit of using the overlap region is that the hybrid solution is not influenced by the exact position of the interface. Our hybrid cycle is a one‐way, state‐based frame and is a major modification of the schemes reported by Wu et al and Schwartzentruber et al . In fact, our hybrid algorithm is the first application of one‐way hybrid coupling to solve the external hypersonic flows.…”

Coupled Navier-Stokes/DSMC Method for Transient and Steady-State Gas Flows

“…[10] and Schwartzentruber and al. [11,12] methods are only suitable for gas flow simulations under steady-state conditions, while the method that we propose has been applied both to transient and steadystate gas flow simulations.…”

“…This method is suitable only in conditions where Kn < 0.1 and the precise formulation of the slip boundary conditions is strongly geometry dependent. For this reason, several hybrid continuum/molecular models have been proposed, for instance: Molecular Dynamics (MD) and Navier-Stokes (N-S) equations [6], Boltzmann and N-S equations [7], Direct Simulation Monte Carlo (DSMC) and Stokes equations [2], DSMC and incompressible N-S equations [8], and DSMC and N-S equations [9,10,11,12,13].…”

“…[10] and Schwartzentruber and al. [11,12] proposed an 'iterative' coupled CFD-DSMC method where the coupling is achieved through an overlapped Schwarz method with Dirichlet-Dirichlet type boundary conditions. However, both Wu and al.…”