Monte Carlo Simulation for Low-Density Hypersonic Flows Past Two- and Three-Dimensional Cavities

The thermal protection system plays a key role in atmospheric re-entry missions of aerospace vehicles. Generally, heat shield plates are assumed to have smooth surfaces. However, discontinuities or cavities exist due to sensor installation, fabrication tolerances and different expansion rates of non-similar materials. This paper tries to investigate low-density hypersonic flows at a group of altitudes, including 70 km, 75 km, 80 km and 90 km, past a flat plate with two- and three-dimensional cavities using the direct simulation Monte Carlo (DSMC) method, with an emphasis to analyze the influence of operation altitude on the flow-field patterns. This work shows that one primary vortex is formed as a result of flow separation and reattachment. In addition, rarefied gas effect plays an important role in flow-field structure and density distributions; as the flight altitude is increased, the primary vortex becomes slender, with its core moving up. Besides, the extra third-dimension precludes external flows from penetrating deep into the cavity, causing the primary vortex to rise, producing a three-dimensional blocking effect. Moreover, as operation altitudes grow, the three-dimensional blocking effect becomes more noticeable.