In order to solve the problem of local aerodynamic heating due to cavities or imperfections on the hypersonic vehicle surfaces

the direct simulation Monte Carlo (DSMC) was employed to investigate a rarefied and hypersonic flow over cavities at the altitudes of 70

75

80km and 90km

while considering the effects of rarefied gas and three-dimensional property on flow-field structure inside the cavity and heat flux over the cavity surfaces. It showed that one primary recirculation region was formed as a result of flow separation and reattachment at aforementioned altitudes. In addition

rarefied gas effect played an important role in flow-field structure and heat flux; as the flight altitude increased

the primary vortex became slender

with its core moving up and top-right-corner part sharpening; and the heat flux consequently concentrated to the top region of the downstream surface of the cavity. Moreover

the inclusion of the third-dimension would preclude main-stream gas molecules from penetrating into the cavity

causing the rise of the core of the primary vortex

and an assumption of two dimensionalities resulted in an overprediction of heat transfer to the cavity surfaces.