DSMC investigation on flow characteristics of rarefied hypersonic flow over a cavity with different geometric shapes

Abstract

As one of the most fundamental configurations, the cavities with different geometric shapes are frequently encountered on various aerodynamic surfaces. In this paper, the direct simulation Monte Carlo (DSMC) which is one of the most successful particle simulation methods in treating rarefied gas dynamics is employed to investigate the flow characteristics of the cavity with a length-to-depth ratio of 1–8, a rearwall-to-frontwall height ratio of 0.5–2, and an inclined frontwall ranging from 20° to 70° for the free stream at a Mach number of 8 and an altitude of 60 km. The simulation results indicate that the shear layer and recirculation region within the cavity are changed greatly by varying length-to-depth ratio and the cavity is transformed into a closed type at the length-to-depth ratio of 6. For the cavity with a fixed length-to-depth ratio, the increase in rearwall height would push the shear layer away from cavity floor and hence increases the area of recirculation region. Conversely, the decrease in rearwall height would draw the shear layer into the interior of the cavity and finally the recirculation region would be split into two smaller and separated ones located at the left and right corners of the cavity respectively. A significant finding is that the criterion (i.e., length-to-depth ratio) for classifying the cavity type is not a constant but changes with freestream conditions. In addition, recirculation region(s) within the cavity can be eliminated completely by simultaneously inclining the frontwall and rearwall with an appropriate angle and meanwhile the shear layer is affected slightly.