Investigation of Mach number and Reynolds number effects on flow around a near-critical geometry prism at Reynolds number <i>O</i>(10<sup>3</sup>) using a low-density wind tunnel

Abstract

In this study, steady drag force measurements and time-resolved schlieren visualization were conducted for subsonic compressible flows around a rectangular cylinder with a side length ratio from 0.5 to 1.2. The effect of the compressibility on the critical geometry was evaluated based on the drag coefficient using a low-density wind tunnel in the Mach number range from 0.1 to 0.6 at the Reynolds number of O(103). In addition, the relationship between the change in the drag coefficient and the flow field was discussed. The side length ratio that the drag coefficient takes the maximum was confirmed to change with the Mach numbers. Remarkably, the peak drag coefficient at the Mach number of 0.6 appears at the side length ratio of 1.0, even though the side length ratio of the critical geometry at the incompressible flow is approximately 0.65. However, the sharp peak in the drag coefficient which is observed in the previous incompressible studies could not be reproduced even at the Mach number of 0.2. This is considered to be due to the lack of the spanwise length of the model or the Reynolds number effects. The schlieren images showed the influence of the Mach number on the location of the vortex formation, and the location moves downstream as the Mach number increases. The change in the flow fields behind rectangular cylinders causes a change in the back pressure, and it might result in a sudden change in the drag coefficient.