ON THE RELATION OF NEAR-WALL STREAMWISE VORTICES TO WALL SKIN FRICTION IN TURBULENT BOUNDARY-LAYERS

Databases from direct numerical simulations of fully developed turbule nt channel flow were used to examine the relation between skin-frictio n on the wall and streamwise vortices observed near the wall. It is sh own that the wall shear rate correlates with streamwise vortices near the wall and that the maximum correlation occurs downstream and with l ateral displacement from the location of skin-friction measurement. Co nditionally averaged statistics taken near high skin-friction regions indicate that the higher skin-friction values are associated with stre amwise vortices located closer to the wall. Visual studies of the time evolution of near-wall streamwise vortices and skin-friction on the w all also indicate that the high skin-friction footprints on the wall c an be attributed to streamwise vortices.