Numerical Analysis of Re-entry Configuration Aerodynamics in the Near Continuum Rarefied Flow Regimes

Abstract

Mature numerical flow solvers based on continuum (Navier-Stokes) and gas-kinetic (Direct Simulation Monte Carlo, DSMC) models are used to study the aerodynamics of a slender re-entry configuration at constant angle of attack with the aim to characterize the practical usability of these approaches in slightly rarefied hypersonic flow. Comparing to recent measurements in the 2nd test section of the continuously operating Hypersonic Vacuum Wind Tunnels Göttingen (V2G) of the German Aerospace Center (DLR), we find that DSMC reproduces the aerodynamic efficiency (ratio of lift to drag) well in the investigated range of free-stream Knudsen numbers 7.2 10−4 < Kn < 7.2 10−3, while the corresponding solutions obtained with the Navier-Stokes solver are systematically too low. Further analysis shows that the continuum method predicts a leeward density that is too high, ultimately leading to an apparent reduction in both lift and drag. Slip boundary conditions are not able to account for this numerical effect. While DSMC must be expected to yield correct aerodynamic coefficients for all degrees of rarefaction, the requirement to resolve kinetic length and time scales makes its computational cost grow quickly as the Knudsen number decreases. We demonstrate that a novel hybrid all-particle approach, combining a kinetic Fokker-Planck algorithm with DSMC, can reduce the required computational effort for low Knudsen numbers while maintaining DSMC-like accuracy, which makes it a promising numerical tool for aerodynamic design.