Flow visualizations and measurements of a three-dimensional supersonic separated flow

The flow along the after body and in the base region of a circular cylinder with a length-to-radius ratio of 3.0 aligned at 10° angle-of-attack to a Mach 2.5 freestream has been investigated experimentally. The objective of this study is 1o better understand the mechanisms that control the base flow for supersonic bodies with a non-zero angle-of-attack orientation. Schlieren and Mie scattering visualizations were obtained to discern governing flow features and to image the large-scale turbulent structure. Surface oil-streak visualizations were obtained to determine the three-dimensionality of the after body surface flow and to deduce the base surface flow field. Pressure-sensitive paint measurements were completed to determine the spatial evolution of surface pressure along the cylindrical body at angle-of-attack and to determine the change in base pressure caused by inclination of the body to non-zero angle-of-attack. Results provide evidence of expected mean-flow features, including base-corner expansions, separated shear layer development, recompression shocks, and a turbulent wake. No evidence of lee-side flow separation was detected along the after body. However, a strong secondary circumferential flow, which develops along the after body due to pressure gradients on its surface, results in the entrainment of fluid into the base region from the leeward portion of the flow. The average base pressure ratio measured for the angle-of-attack case is 48.4% lower than that measured for zero angle-of-attack, resulting in a significant increase in base drag for cylindrical objects inclined at angle-of-attack.