All-Particle Multiscale Computation of Hypersonic Rarefied Flow.

Abstract

Hypersonic aerothermodynamics for a probe entering a planetary atmosphere is an important issue in space exploration. The probe experiences various Knudsen number regimes, ranging from rarefied to continuum, due to density variation in the planet's atmosphere. To simulate such multiscale ows, a novel hybrid particle scheme is employed in the present work. The hybrid particle scheme employs the direct simulation Monte Carlo (DSMC) method in rareed ow regions and the low diffusion (LD) particle method in continuum ow regions. Numerical procedures in the low diffusion particle method are implemented within an existing DSMC algorithm. The hybrid scheme is assessed by studying Mach 10 nitrogen ow over a sphere with a global Knudsen number of 0.002. Standard DSMC and CFD results are compared with the LD-DSMC hybrid simulation results. The hybrid scheme results show good overall agreement with results from standard DSMC computation, while CFD is inaccurate especially in the wake where a highly rareed region exists. The LD-DSMC hybrid solution is able to increase computational effciency by 20% in comparison to DSMC. Also, sensitivity to numerical parameters of the LD-DSMC method is studied by using Mach 40 carbon dioxide ow over a Mars entry spacecraft. Finally, a module initializing the LD-DSMC hybrid method with a Navier-Stokes solution is studied. The conventional LD-DSMC initializes with standard DSMC until the first continuum breakdown occurs. The main alternative to hybrid LD-DSMC simulation is a CFDDSMC hybrid simulation that is significantly faster because it initializes the method decomposition by evaluating breakdown based on an initial CFD solution. The initialized solution agrees well with DSMC and the conventional LD-DSMC methods and requires only 56 % of the resources of the conventional LD-DSMC simulation.