Tracking of vortices in a turbulent boundary layer

Abstract

The motion of spanwise vortical elements has been tracked in the outer region between wall-normal distance z/δ = 0.11 and 0.30 of a turbulent boundary layer at Reθ = 2460. The experimental dataset of time-resolved threedimensional velocity fields used has been obtained by tomographic particle image velocimetry. The tracking of these structures yields their respective average trajectories as well as the variations thereof, quantified by the root-mean-square of the trajectory coordinates as a function of time. It is demonstrated that the variation in convection can be described by a dispersion model for infinitesimal particles in homogeneous turbulence, which suggests that these vortical structures are transported passively by the external velocity field without significant changes in their topology, at least over the present observation time of 1.2δ/Ue. It is shown that the measured variation in convection velocity can further be used successfully to predict the temporal development of space-time correlation functions starting from the instantaneous correlation map. In this prediction the structures are assumed to convect without change, following our observations.