Fundamental Physics of Polymer-Turbulence Interactions underlying Drag Reduction, from Homogeneous Shear Flow DNS with the FENE-P Model

James G. Brasseur
Professor of Mechanical Engineering, Bioengineering and Mathematics
Department of Mechanical Engineering
Pennsylvania State University

Polymers injected at low concentrations into boundary layers dramatically reduce skin friction independently of whether the wall is smooth or rough, indicating that the essential mechanisms that suppress momentum flux, and therefore drag, originate outside the viscous surface layer. We propose that, although other effects modulate drag reduction, the essential mechanisms that suppress momentum flux arise from the modulation of polymer-turbulence interactions by mean shear, and therefore that the primary drag-reducing interactions take place in the lower inertial wall layer where shear Weissenberg number maximizes. To validate this hypothesis and to study the more fundamental polymer-turbulence dynamics that lead to drag reduction, I will discuss a wide range of well-resolved simulations of polymer-laden shear-driven homogenous turbulence with the FENE-P model over a wide range of Weissenberg numbers and concentration parameters. We apply a specialized algorithm that overcomes the need for numerical dissipation to maintain stability. I shall present in-depth analyses relevant to fundamental mechanisms in the initial and equilibrium states and in the “maximum drag reduction” (MDR) limit.