Abstract
Conditional averages of streamwise, lateral, spanwise velocity and of their products have been examined by using a VITA technique to study the well-organized vortical structures associated with the bursting phenomenon, in the turbulent boundary layer over a d-type rough surface at a momentum thickness Reynolds number of Rθ≒800. The ensemble averaged patterns suggest that pairs of counter-rotating streamwise vortices associated with the ejection events probably exist in the wall region of a present rough wall flow but occur randomly in space and time, and that broad large scale three-dimentional vortical motions associated with the sweep events move around the low speed streak as the sweep passes over the wall region. These vortical structures are associated with high Reynolds shear stress and also high streamwise vorticity and hence make a significant contribution to turbulent-energy production.
