Velocity Slip and Temperature Jump in Hypersonic Aerothermodynamics

Abstract

Hypersonic vehicles experience different flow regimes during flight due to changes in atmospheric density. Computational fluid dynamics, although relatively computationally inexpensive, is not physically accurate in areas of highly nonequilibrium flows. The direct simulation Monte Carlo method, although physically accurate for all flow regimes, is relatively computationally expensive. In a continuing effort to understand the performance of computational fluid dynamics and direct simulation Monte Carlo in hypersonic flows, the current study investigates the effect of continuum breakdown on surface aerothermodynamic properties (pressure, shear stress, and heat transfer rate) of a cylinder in Mach-10 and Mach-25 flows of argon gas for several different flow regimes, from the continuum to a rarefied gas. Several different velocity-slip and temperature-jump boundary conditions are examined for use with the computational fluid dynamics method. Computational fluid dynamics and direct simulation Monte Carlo solutions are obtained at each condition. Total drag and peak heat transfer rate predictions by computational fluid dynamics remain within about 6% of the direct simulation Monte Carlo predictions for all regimes considered, with the Gökçen-type slip condition giving the best results.

New temperature jump boundary condition in high-speed rarefied gas flow simulations

“…The accommodation coefficients represent the fraction of incoming DSMC particles that are reflected diffusely, and the remainder are reflected specularly. Velocity slip and translational temperature jump are calculated with the accommodation coefficients of unity as presented in [13,14],…”

Computation of Hypersonic Flows Using the Direct Simulation Monte Carlo Method

“…Specifically, it is assumed that the gas viscosity is described by a simple temperature relation: (10) and the relationship between the reference parameters is provided by Bird [6]. Values of these reference parameters for many common species are listed in [6], and these are generally obtained by comparison with measured or computed viscosity data.…”

“…These effects are naturally included in a DSMC simulation using the diffuse reflection and CLL models, whereas the usual approach for CFD is to assume no slip and no temperature jump at a wall. The omission of these high-Knudsen-number surface phenomena in CFD partially explains some of the differences noted in the detailed comparisons under hypersonic flow conditions of DSMC and CFD reported in [9,10]. One approach to try and extend the usefulness of CFD into the high-Knudsen-number range is to employ velocity slip and temperature jump models; see for example [10].…”

“…Detailed studies [9][10][11] have compared DSMC and computational fluid dynamics (CFD) computations of hypersonic flows over cylinders and wedges for global Knudsen numbers ranging from continuum (Kn 0.002) to rarefied (Kn 0.25). Every effort was made in these studies to employ consistent cross sections and transport models in DSMC and CFD, respectively.…”

Aerothermodynamics analysis of the electromagnetically launched projectiles under rarefied gas conditions

“…The reports of the hypersonic flight studies in the rarefied gas conditions reveal that continuum based CFD solvers are not valid in this flow regime [5]. In a closely related study, pressure and heat transfer rate values of a 2-dimensional cylinder body is calculated in Mach 10 and Mach 25 using molecular based direct simulation Monte Carlo method (DSMC) [6]. However, these works are limited to simple cylinder bodies.…”