Hypersonic Aerothermodynamics Analysis Across Nonequilibrium Regimes Using Continuum and Particle Methods

Abstract

Hypersonic vehicles experience different flow regimes during flight due to changes in atmospheric density. Computational Fluid Dynamics (CFD) is not physically accurate in areas of highly non-equilibrium flows. The direct simulation Monte Carlo (DSMC) method, while physically accurate for all flow regimes, is relatively computationally expensive. In a continuing effort to understand the performance of CFD and DSMC in hypersonic flows, the current study investigates the effect of non-equilibrium on surface aerothermodynamic properties (pressure, shear stress and heat transfer rate) of a cylinder in Mach 10 and Mach 25 flows of nitrogen gas for several different flow regimes, from the continuum to a rarefied gas. Vibrational relaxation models used in each solution method are compared. CFD (with slip and temperature jump boundary conditions) and DSMC solutions are obtained at each condition. Non-equilibrium between internal energy modes and the translational mode do not have a large effect on surface property prediction, as total drag and peak heat transfer rate predictions by CFD remain within about 3% and 8%, respectively, of the DSMC predictions for all regimes considered.

Effects of Continuum Breakdown on the Surface Properties of a Hypersonic Sphere

“…A more recent study by Lofthouse et al examined the effects of velocity slip and temperature jump at the surface of a 2-D 12-in.-diam cylinder in Mach 10 and 25 flow of argon [9]. Another study by Lofthouse et al investigated Mach 10 and 25 nitrogen flow over a cylinder [10]. All of these studies were conducted over a range of Knudsen numbers, 0.002-0.25, in which the characteristic length is taken to be the diameter of the cylinder.…”

Hypersonic Flow Over a Flat Plate: CFD Comparison with Experiment

“…Previous work by the authors comparing CFD and DSMC focused purely on numerical results, with CFD simulations being compared directly to DSMC simulations. [7][8][9][10] In particular, the walls were assumed to be fully diffusive; that is, the gas molecules colliding with the wall were assumed to accommodate fully to the wall conditions. Hence, an accommodation coefficient of unity was used for the CFD slip boundary conditions.…”

Effects of continuum breakdown on hypersonic aerothermodynamics for reacting flow

“…It has been found that the probability can better correspond with theory by multiplying by a simple factor that is dependent on the maximum temperature. 6 Unfortunately, this method does not work for multiple species and in fact was only employed for N 2 -N 2 vibrational relaxation. 7 For multiple species, a more elegant solution has been included in the DSMC method to be able to obtain the proper vibrational relaxation rate.…”

“…It was also observed that velocity slip and temperature jump boundary conditions improved the agreement between the two numerical methods. Another study by Lofthouse et al 6 investigated Mach 10 and 25 nitrogen flow over a two-dimensional cylinder. That study was again conducted over a range of Knudsen numbers from continuum to rarefied flow.…”