Study on local topology model of low/high streak structures in wall-bounded turbulence by tomographic time-resolved particle image velocimetry

The relationship between the bursting event and the low/high-speed streak in the logarithmic law (log-law) region of a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry (TRPIV) system is used to measure the instantaneous three-dimensional-three-component (3D-3C) velocity field. The momentum thickness based Reynolds number is about 2 460. The topological information in the log-law region is obtained experimentally. It is found that the existence of the quadrupole topological structure implies a three-pair hairpin-like vortex packet, which is in connection with the low/high-speed streak. An idealized 3D topological model is then proposed to characterize the observed hairpin vortex packet and low/high-speed streak.