Computational Analysis of a Rarefied Hypersonic Flow over Backward-Facing Steps

This work deals with a numerical study on backward-facing steps situated in a nonreacting low-density hypersonic flow. The work is motivated by the interest in investigating the impact on the aerodynamic surface quantities of surface discontinuities on hypersonic vehicles. Discontinuities are represented by backward-facing steps with boundary-layer thickness larger than the step height at the step position. The primary emphasis is to assess the sensitivity of the heat transfer, pressure, and skin friction coefficients. In doing so, these effects have been investigated by employing the direct simulation Monte Carlo (DSMC) method. The analysis showed that the flow past a backward-facing step in hypersonic flow is characterized by a strong expansion on the corner of the step, which influences the downstream separation region and the aerodynamics surface properties downstream of the back face. It was found that the recirculation region behind of the steps is a function of the back-face height, for the conditions investigated. In addition, the heat flux to the surface and the wall pressure increased in the reattachment zone downstream of the back face and reached the flat plate values in a smooth fashion. A comparison of the present simulation results with experimental data showed close agreement concerning the heat flux to step surface.