Synergy in the organization of near-wall and bulk turbulence structures in viscoelastic turbulent channel flow in the high drag reduction regime

Structures in polymer drag-reduced turbulence have been examined by using a direct numerical simulation of viscoelastic turbulent channel flow for a high drag reduction (HDR) rate of ∼60%. In drag-reduced flow, the length scale of turbulence structures significantly increases, especially in the streamwise direction. Moreover, the outer turbulence structures in the viscoelastic flow differ from those in Newtonian flow. Two-point correlations and conditionally averaged flow fields suggest that in HDR flow, near-wall structures for both upper and lower walls can be organized by an outer-region co-supporting cycle whose wall-normal extent is approximately equal to the height of the whole channel.