Session MA - Turbulent Boundary Layers V.
MIXED session, Tuesday afternoon, November 23
Grand I, Westin Seattle
Dual-plane PIV was employed in a turbulent boundary layer at Re_\tau \sim 1100 to study the nature of the vortical structures there. Laser sheets separated by 1 mm were aligned in streamwise-spanwise (x,y) planes, and the scattered light was captured by three cameras: two in a stereo configuration and one in a normal configuration. All velocity gradient components were determined for fields in the log (z^+ = 125) and outer (z/\delta = 0.5) regions. Three-dimensional swirl strength was used to isolate vortex cores, and the vorticity direction of individual swirl centers was determined. Instantaneous fields in the log region reveal signatures of hairpin vortex packets consistent with previous results. The packets contain evidence of smaller hairpin heads embedded within the long low-speed regions surrounded by larger hairpins. The data set at z^+ = 125 yielded a most probable hairpin inclination angle of 32^\circ and an average inclination angle of 57^\circ. In the presentation, these results will be contrasted with those at z/\delta = 0.5.