Measurements and visualizations of a three-dimensional compressible base flow

Three-dimensional compressible base flows are created during the supersonic flight of cylindrical aerodynamic bodies at non-zero angle-of-attack. In the present study, the flow along the afterbody and in the base region of a circular cylinder with a length-to-radius ratio of 3.0 aligned at a 10° angle-of-attack to a nominal Mach 2.5 freestream has been investigated experimentally. The fundamental objective of this investigation is to better understand the fluid dynamic mechanisms that govern the behavior of the base flow for supersonic bodies with a nonzero angle-of-attack orientation. Experimental techniques employed in this study include: flow visualizations, surface-pressure measurements, and instantaneous velocity measurements.; Flow visualizations provide evidence of expected mean-flow features, including a shock/expansion discontinuity of circumferentially varying strength at the angular discontinuity, a base-edge expansion fan, a separated shear layer, an asymmetric recirculation region, and a turbulent wake. A strong secondary circumferential flow, which develops along the afterbody due to pressure gradients on its surface, results in the entertainment 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. Three-dimensional effects in the developing afterbody boundary layer result in significantly faster growth of the boundary layer in the leeward plane compared to the windward plane. In the base region, a very short recirculation region is measured, with the axial distance to the stagnation point location reduced by 55% from the axisymmetric case. The separated shear layer grows to a much greater thickness in the leeward region than in the windward region. In addition, the leeward portion of the shear layer converges on the radial centerline of the flow at a more severe angle than the windward shear layer, resulting in a shift of the reattachment region towards the windward portion of the flow. The peak turbulent stresses are located downstream of the reattachment point, in contrast to axisymmetric results, where maximum stresses are measured on the inner edge of the shear layer prior to reattachment.