Recommended direct simulation Monte Carlo collision model parameters for modeling ionized air transport processes

Abstract

A systematic approach for calibrating the direct simulation Monte Carlo (DSMC) collision model parameters to achieve consistency in the transport processes is presented. The DSMC collision cross section model parameters are calibrated for high temperature atmospheric conditions by matching the collision integrals from DSMC against ab initio based collision integrals that are currently employed in the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) and Data Parallel Line Relaxation (DPLR) high temperature computational fluid dynamics solvers. The DSMC parameter values are computed for the widely used Variable Hard Sphere (VHS) and the Variable Soft Sphere (VSS) models using the collision-specific pairing approach. The recommended best-fit VHS/VSS parameter values are provided over a temperature range of 1000-20 000 K for a thirteen-species ionized air mixture. Use of the VSS model is necessary to achieve consistency in transport processes of ionized gases. The agreement of the VSS model transport properties with the transport properties as determined by the ab initio collision integral fits was found to be within 6% in the entire temperature range, regardless of the composition of the mixture. The recommended model parameter values can be readily applied to any gas mixture involving binary collisional interactions between the chemical species presented for the specified temperature range.

Comparison of CFD and DSMC using calibrated transport parameters

“…The collision integrals and the ratio of collision integrals can be expressed 5 in terms of the VHS parameters as:…”

“…This will be examined later in this work. Previous work 5 has provided a recommended set of DSMC collision model parameters for both neutral (6-species) and ionized (13-species) gas mixtures based on calibrations against ab initio-based collision integral data. The VHS and VSS parameters are input quantities that may be specified for each species, or for each collision pair.…”

“…Efforts have recently begun to develop a hybrid framework for combined continuum/rarefied high speed flows [4][5][6] that is coupled in physical space. The first step is to be able to accurately define locations in the flow field where continuum breakdown is occurring, by employing continuum breakdown parameters.…”

“…Once a boundary has been defined, an approach for the generation of particles has been developed in which the fluxes of mass, momentum, and energy determined from the NS solution are used to prescribe the appropriate velocity distribution function to be used within the DSMC particle generation process 4 . The next challenge is to ensure consistency between CFD and DSMC with respect to transport properties and other non-equilibrium phenomena, such as internal energy relaxation and chemical processes A systematic approach for calibrating the DSMC collision model parameters to achieve consistency in the transport process was therefore developed and has been used to generate best-fit variable hard sphere (VHS) and variable soft sphere (VSS) parameter values for air systems 5 .…”

Transport properties of carbon-phenolic gas mixtures

“…Computing the transport properties of these reduced sets requires atomic and molecular data for the species collision pairs [20][21][22] . Intermolecular potential data such as the well depth and reference length are used to calculate the collision integrals that appear in the expressions for the species transport properties.…”