Near-wall bursting phenomena and quasi-streamwise vortex models

Near-wall bursting phenomena have been detected both by the VITA technique and by a quadrant analysis. In addition to these detection schemes, visual burst detection has been performed in order to characterize the difference between VITA events and Q2 (second quadrant) events. It is shown that the spanwise yaw angle of visualized low-speed streaks for VITA events is greater than for Q2 events. Based on the experimental findings and the Euler equation, quasi-streamwise vortex models are proposed, and the results are compared with the experiments. Fluctuating velocity signals computed from the models are in good agreement with the experimental data for VITA events. Contour plots of the calculated axial velocity, spanwise vorticity and instantaneous Reynolds shear stress are presented. The generation processes of shear layer structures and Q2 and Q4 motions are demonstrated.