Schlieren visualization of transonic and supersonic flow over a sphere at reynolds number between 10³and 10⁵through free-flight tests

In this study, free-flight tests of a sphere at a Reynolds number between 5.7 × 10³and 3.1 × 10⁵under transonic to supersonic condition is conducted using ballistic range and investigate the flow over a sphere under compressible low-Reynolds number conditions. The flow visualization is carried out by schlieren technique. A free-flight Reynolds number is between 5.7 × 10³and 3.1 × 10⁵and a free-flight Mach number is between 0.9 and 1.6. To realize the compressible low-Reynolds number flow, the flow visualization is carried out under low-pressure conditions with a small sphere (minimum diameter is 2.0 mm). in addition, the time-averaged images around a sphere are obtained and compared with previous numerical results for the Reynolds number between 50 and 1000. From the experimental results, the near field and far field flow structure at the Reynolds number of between 5.7 × 10³and 3.1 × 10⁵under supersonic conditions are visualized. As a result, following characteristics are clarified: 1) the perturbation amplitude of wake vortex is attenuated as a free-flight Mach number increases, 2) mode of wake structure is changed by changing the free-flight Mach number, 3) there is no Reynolds number dependences on the separation point, but a length of the recirculation region is influenced by the Reynolds number.