Eulerian and Lagrangian views of a turbulent boundary layer flow using time-resolved tomographic PIV

Abstract

Coherent structures and their role for the fluid exchange mechanisms in the logarithmic region of a turbulent boundary layer are the focus of the present paper. Experiments have been performed in the water tunnel at TU Delft measuring the particle motion within a volume of a turbulent boundary layer flow along a flat plate at a free stream velocity of 0.53 m/s at Re ~ 2460 based on momentum thickness by using time-resolved- tomo particle image velocimetry (PIV) and particle tracking velocimetry (PTV) . The obtained data enables an investigation of the flow structure topologies within a temporally and spatially resolved Eulerian 3D reference frame. Flow statistics of physically relevant quantities have been evaluated in terms of probability density functions (PDF´s), space-time-correlations and conditional averaging. An analysis of single events has been performed in order to enhance the understanding of wall-bounded turbulence and highlight the potential of this novel technique for turbulence characterisation. A validity check of Taylor’s frozen turbulence hypothesis has been established by two-point-correlation functions between the measured and hypothetical reconstructed components of velocity. Furthermore a PTV algorithm has been applied on the time sequences of reconstructed 3D particle image distributions identifying thousands of particle trajectories which enable the calculation of PDF’s of the three components of Lagrangian accelerations.