Assessment of Gas-Surface Interaction Models in DSMC Analysis of Rarefied Hypersonic Flow

Abstract

The aerothermodynamics of spacecraft entering a planetary atmosphere are sensitive to the level of gas-surface accommodation governed by the gas-surface interaction. The modeling of this interaction plays an integral role in the solid surface boundary condition of the Direct Simulation Monte Carlo (DSMC) method. The Maxwell, and Cercignani, Lampis and Lord (CLL) gas-surface interaction models are examined. Existing windtunnel test results of rarefied hypersonic flow over flat surfaces enable the assessment of these gassurface interaction models for DSMC simulations for this kind of flow condition. These models gave the same boundary layer velocity profiles at 50 % to full gas-surface accommodation. Approximately, 90 % gas-surface accommodation yielded the overall best agreement between the simulations and windtunnel data, reported by Cecil and McDaniel [AIAA Paper 2005-4695]. Regarding molecular velocity distributions next to the surface, the gas-surface interaction models result in similar horizontal component distributions, but distinct vertical component distributions. Molecular velocity distributions also reveal translational nonequilibrium very near the surface due to surface reflected molecules, within 5 local mean-free-paths above the surface. Within a region of significant translational nonequilibrium, the distributions are better characterized by the most probable value, rather than the mean value. Regarding scattering distributions, the Maxwell model results in distributions with unrealistic peaks due to specular reflection; however, the CLL model results in petal-shaped distributions, similar to observations of molecular beam studies. Moreover, while the Maxwell scattering distributions experienced abrupt changes with increasing accommodation and position, the CLL distributions varied smoothly. Nevertheless, both yield good agreement with the PLIF windtunnel test boundary layer velocity profiles using a proper specification of gas-surface accommodation.