Characteristics of vortex packets in turbulent boundary layers

Abstract

Stereoscopic particle image velocimetry (PIV) was used to measure all three instantaneous components of the velocity field in streamwise-spanwise planes of a turbulent boundary layer at Reτ = 1060 (Reθ = 2500). Datasets were obtained in the logarithmic layer and beyond. The vector fields in the log layer (z+ = 92 and 150) revealed signatures of vortex packets similar to those proposed by Adrian and co-workers in their PIV experiments. Groups of legs of hairpin vortices appeared to be coherently arranged in the streamwise direction. These regions also generated substantial Reynolds shear stress, sometimes as high as 40 times -ūw. A feature extraction algorithm was developed to automate the id..