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

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-deg angle of attack to a nominal Mach 2.5 freestream has been investigated experimentally. The ob jective is to better understand the mechanisms that control base flow for s upersonic bodies with a nonzero-angle-of-attack orientation, Laser Doppler velocimetry measurements were conducted in the incoming boundary layer to q uantify the initial conditions at the onset of three-dimensional behavior. Schlieren and Mie scattering visualizations were obtained to discern govern ing how features and to image the large-scale turbulent structures of this separated flow. Surface oil-streak visualizations were obtained to determin e the three dimensionality of the afterbody surface flow and to deduce the base surface flowfield. Pressure-sensitive paint measurements were complete d to determine the spatial evolution of surface pressure along the cylindri cal body at angle of attack and to determine the change in base pressure ca used by inclination of the body. Results provide evidence of expected mean- how features, including base-corner expansions, separated shear layer devel opment, recompression shocks, and a turbulent wake, No evidence of lee-side Buff separation was detected along the afterbody, However, a strong second ary circumferential flow, which develops along the afterbody due to pressur e gradients on its surface, results in the entrainment of fluid into the ba se region from the lees ard portion of the flow. The average base pressure ratio measured for the angle of attack case is 48.4% lower than that measur ed fur zero angle of attack, resulting in a significant increase in base dr ag for cylindrical objects inclined at angle of attack.