Effects of continuum breakdown on hypersonic aerothermodynamics

Hypersonic vehicles experience different flow regimes during flight due to changes in atmospheric density. Hybrid continuum-particle methods, based on computational fluid dynamics (CFD) and direct simulation Monte Carlo (DSMC) methods, are being 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 These methods use a breakdown parameter to determine regions of the flow where the CFD physics are no longer valid.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 aerothermodynamic properties (pressure, shear stress, and heat transfer rate) of a cylinder in a Mach 10 flow of argon gas for several different flow regimes, from the continuum to a rarefied gas. CFD and DSMC solutions are obtained at each flow condition. Total drag predictions differ by less than 1% for a continuum flow while CFD predicts a 26% higher drag than DSMC for a rarefied flow. Peak heat transfer rate differences range from less than 1% for a continuum flow to more than 32% for a rarefied flow, again with CFD predicting the higher value. Differences in drag and heat transfer are expected to decrease with the use of velocity slip and temperature jump boundary conditions with the CFD method. (c) 2007 American Institute of Physics.