Assessment of an All-Particle Hybrid Method for 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 flows, a novel hybrid particle scheme is employed in the present work. The hybrid particle scheme employs the direct simulation Monte Carlo (DSMC) method in rarefied flow regions and the low diffusion (LD) particle method in continuum flow 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 flow 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 rarefied region exists. The LD-DSMC hybrid solution is able to increase computational efficiency by 20% in comparison to DSMC. Also, a module initializing the LD-DSMC hybrid method with a Navier-Stokes solution is developed. The initialized solution agrees well with DSMC and requires only 45% of the resources.

Comparative Study Between Cubic and Ellipsoidal Fokker–Planck Kinetic Models

“…The maximum normalized gradient of macroscopic values found from Eqs. 21 and 22 is analyzed for each grid resolution [23] and an adaptive mesh was therefore employed for a design of an efficient grid configuration. As described in Eq.…”

Progress in particle-based multiscale and hybrid methods for flow applications

“…The results compared well to the reference solution and the speed-up for the Mach 20 cylinder flow was given to be about 2.6 higher compared to a full DSMC simulation. Jun et al (2013) calculated the flow around a cylinder as well, this time at Mach 10. Compared to a full DSMC simulation, their speed-up was only about 1.2 using the same method as described above.…”

“…Different mesh densities and time steps for the respective solver were used in order to speed up the calculation. The initial solution on which the domain has been separated into rarefied and continuum regime was obtained by the Navier-Stokes equations as they have previously proven to provide the initial solution in a shorter time (Jun et al 2013). It has been mentioned that the mean free path varied over one order of magnitude for the cylinder-flare case (speed-up 1.4) and over two orders of magnitude for the blunt planetary probe (speed-up 12.5), where the speedup in parenthesis are comparing to full DSMC simulations.…”