The gas dynamic features of the laminar, near-wake flow behind slender and blunt hypersonic vehicles are studied using the direct simulation Monte Carlo method. Near-wake flows are characterized by features of low density, low Reynolds number, high temperature, thermal nonequilibrium, species separation, and recirculation. The impact of freestream number density and velocity on the near-wake flowfield is considered and compared for slender and blunt bodies. The near-wake structure postulated by theory and observed in numerical continuum calculations is also observed in the kinetic simulations, which are more accurate in the high-altitude, rarefied near-wake flow. The paper discusses the validation of the direct simulation Monte Carlo computational tool with experimental data for slender and blunt shapes and a previously published blunt direct simulation Monte Carlo geometry case. Then, the near-wake flows generated by a 10 deg slender cone and a 70 deg blunt body are analyzed. The near-wake flows behind slender and blunt bodies are similar in that the freestream Mach number has little impact on the near-wake flow structure and the recirculation length is not found to be related to the local Reynolds number. For both geometries, the base radius was found to be the characteristic length in the near-wake flow. Significant differences in the near-wake flow for the two geometries were observed in the spatial distribution of gas temperatures, the degree of chemical dissociation, and the sensitivity of recirculation length to freestream number density.
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