An experimental investigation on coherent structures in near wall region of channel turbulent flow using DPIV

The channel turbulence isstudied experimentally by using a double frame straddling CCD camera DPIV system. Throughthe analysis of enormous data obtained from the experiment,the spatial structure and its evolution characteristics, together withthe time history ofturbulence in the near wall region, are obtained. The experimental resultreveals that the phenomena such as ejection, sweep and variety ofinstantaneous velocity profiles of turbulence bear a direct physical relationwith the evolution of the clockwise transverse vortex flowing downstream. Theexperimental result explains the form and the evolution of inflexion ofthe instantaneous velocity profile when the clockwise transverse vortexpasses through it. From the experimental result, we can explain some characteristicmechanism of large scale structure. The experimental result also shows thatDPIV system can provide quantitative and qualitative informationconcerning turbulence spatial characteristics and is suitable forexperimental studies on turbulence in the near wall region.