Nonlinear travelling waves as a framework for understanding turbulent drag reduction

Nonlinear travelling waves that are precursors to laminar–turbulent transition and capture the main structures of the turbulent buffer layer have recently been found to exist in all the canonical parallel flow geometries. We study the effect of polymer additives on these ‘exact coherent states’ (ECS) in the plane Poiseuille geometry, focusing on Reynolds numbers slightly above transition. Many key aspects of the turbulent drag reduction …