On aerodynamic characteristics of rarefied hypersonic flows over variable eccentricity elliptical cavities

Abstract

A comprehensive numerical study is performed to reveal the pressure on and heat flux to elliptical cavity surfaces using the direct simulation Monte Carlo method with the influences of elliptical cavity eccentricity, freestream altitude, freestream Mach number, and upstream wall curvature analyzed in detail. The obtained results show that both the high-pressure and high heat flux areas are located around the top lip of the downstream sidewall of an elliptical cavity, and whose peak pressure and peak heat flux are usually tens of times larger than those on the cavity floor; the depth of the high-pressure and high heat flux areas moving to the cavity floor is determined by the half axis length in streamwise, while the width of the two areas is controlled by that in spanwise. Compared with the cylindrical cavity, the elliptical cavity has slightly smaller peak pressure and peak heat flux on the downstream sidewall but has much smaller values on the cavity floor. For two elliptical cavities with the same eccentricity, the one that has a shorter length in streamwise is overall better in reducing the surface pressure and heat flux. The freestream altitude and Mach number also play an important role in affecting the surface pressure and heat flux. In comparison with the horizontal upstream wall, the convex upstream wall reduces the peak pressure and peak heat flux on the downstream sidewall but greatly raises them on the cavity floor, and the concave upstream wall makes them drop sharply in the form of a cliff no matter on the downstream sidewall or on the cavity floor. The physical mechanism behind the wall curvature effect can be explained as follows: surface pressure and heat flux on the downstream sidewall are originated from the violent impact of the external high-speed airstream on the sidewall, while those on the cavity floor are derived from the friction between the rotating vortices inside the cavity and the cavity floor.