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

Abstract

The e ow 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 objective is to better understand the mechanisms that control base e ow for supersonic bodies with a nonzeroangle-of-attack orientation. Laser Doppler velocimetry measurements were conducted in the incoming boundary layer to quantify the initial conditions at the onset of three-dimensional behavior. Schlieren and Mie scattering visualizations were obtained to discern governing e ow features and to image the large-scale turbulent structures of this separated e ow. Surface oil-streak visualizations were obtained to determine the three dimensionality of the afterbody surface e ow and to deduce the base surface e owe eld. 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. Results provide evidence of expected mean-e ow features, including base-corner expansions, separated shear layer development, recompression shocks, and a turbulent wake. No evidence of lee-side e ow separation was detected along the afterbody. However, a strong secondary circumferentiale ow, which developsalong theafterbody dueto pressuregradientsonitssurface, results in the entrainment of e uid into the base region from the leeward portion of the e ow. 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 signie cant increase in base drag for cylindrical objects inclined at angle of attack.