Effects of Continuum Breakdown on Hypersonic Aerothermodynamics

Abstract

Hypersonic vehicles experience different flow regimes during flight due to changes in atmospheric density. Hybrid Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) methods are developed to simulate the flow in different hypersonic regimes. These methods use a breakdown parameter to determine regions of the flow where the CFD physics are no longer valid. The current study investigates the effect of continuum breakdown on surface properties, such as pressure, shear stress and heat transfer rate, on a cylinder in a Mach 10 flow of argon gas for several different flow regimes, from the continuum to a rarefied gas. The difference in total drag ranges from 0.5% for a continuum to 26.2% for a rarefied gas. Peak heat transfer rate differences ranges from nearly 4% for a continuum to almost 32% for a rarefied gas. Drag depends primarily on continuum breakdown in the wake, while heat transfer rate appears to depend primarily on continuum breakdown in the shock and differences in thermal boundary layer thickness. I. Introduction A hypersonic vehicle such as a planetary entry capsule or a reusable launch vehicle, will experience vastly different flow regimes during the course of its flight trajectory because the earth's atmosphere varies in density as a function of altitude. Reproduction of these varied flow conditions in ground-based laboratory facilities is both expensive and technically challenging. Hence, there is an extremely important role for computational models in the development of hypersonic vehicles.

Hybrid Particle-Continuum Simulations of Nonequilibrium Hypersonic Blunt-Body Flowfields

“…These results are qualitatively and quantitatively similar to those presented in Ref. 24 for simulations of Mach 10 flow of argon around a cylinder. However, as shown in that study, the coefficient of pressure (C p ) predicted by both NS and DSMC is virtually the same.…”

pdFOAM: A PIC-DSMC code for near-Earth plasma-body interactions

“…A comparison of MONACO with other established DSMC codes for [38]'s Kn = 0.009 case show a 2.7% underprediction of peak heat flux is within the code-tocode uncertainty reported in [8]. …”

“…They investigated a Mach (M ) 10 flow of Argon (Ar) over a two-dimensional, 12 in (0.3048 m) diameter cylinder with a fixed surface temperature of 500 K for a variety of Kn by varying the freestream number density (n ∞ ). The following sections outline the numerical setup of pdFOAM and compare with results in [38].…”

“…The Mach 10 Kn = 0.2 cylinder case from [38] is repeated and compared with data from MONACO [19], an established DSMC code. 2.…”

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

“…They referred to Bird (1970) who showed that Kn GLL > 0.05 implies a departure from the continuum behaviour. Lofthouse et al (2007) investigated a Knudsen number range of 0.002 < Kn ≤ 0.25 for a Mach 10 flow around a cylinder using two independent solver: one based on the NavierStokes equations and the other on the DSMC method. They calculated the pressure, shear stresses and heat transfer on the cylinder surface and correlated the results with the local Kn GLL to judge whether the region can be treated as a continuum or not.…”