Velocity measurements in a three-dimensional compressible base flow

The velocity field 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 objective of this study is to better understand the mechanisms that govern the characteristics and development of three-dimensional, compressible base flows. Laser Doppler velocimetry was used to measure both mean velocity components and turbulence statistics. The results reveal all expected base flow features, including: a low-speed recirculation region, a separated shear layer, a reattachment region, and a trailing wake. The distance from the base to the rear stagnation point in this three-dimensional base flow is reduced by 55% as compared to the corresponding axisymmetric base flow. The shear layer in the leeward region of the flow turns sharply towards the radial centerline, resulting in a shift of the flow stagnation location towards the windward side of the base flow. In addition, the shear layer in the leeward plane thickens at a substantially faster rate than in either the windward or side planes. The turbulent stresses in the windward region of the shear layer are higher in magnitude than observed in either the leeward or side regions. The peak stresses measured in this threedimensional base flow are located in the reattachment region, in direct contrast to axisymmetric results, where peak stresses were measured in the shear layer just upstream of reattachment.