The structure of the vorticity field in turbulent channel flow. Part 2. Study of ensemble-averaged fields

Several conditional-sampling techniques are applied to data bases generated by large-eddy and direct numerical simulations. It is shown that the bursting process is associated with well-organized vortical structures inclined at about 45° to the wall. These vortical structures are identified by examining the vortex lines of three-dimensional instantaneous and ensemble-averaged vorticity fields. Two distinct horseshoe-shaped vortical structures corresponding to the sweep and ejection events are detected. These vortical structures are associated with high Reynolds shear stress and hence make a significant contribution to turbulent-energy production.