Stereoscopic Particle Image Velocimetry Investigation of Three-Dimensional Characteristics of Vortex Structure in a Turbulent Channel Flow

We investigate the three-dimensional characteristics of turbulence structures in a turbulent channel flow by employing stereoscopic particle image velocimetry (SPIV). The SPIV measurement was performed for a water flow at the Reynolds number Re = 1.1×10⁴ in both the streamwise--spanwise (x--z) and spanwise--wall-normal (z--y) planes, respectively. A three-dimensional image of the vortex tubes or the hairpin vortex leg(s) inclined toward the wall was obtained. A series of wall-normal vortex cores were found to align with the low-speed streaks with opposite vorticity signals at both sides of the streaks in the x-z plane, which were cross-section slices of the inclined hairpin vortex leg(s).