Direct numerical simulation on drag-reducing flow by polymer additives using a spring-dumbbell model

A discrete-element model (spring-dumbbell model) is used to investigate the mechanism of drag-reduction by adding polymer in a turbulent channel flow of Newtonian fluid by Direct Numerical Simulations (DNSs). By using this model, the spatial concentration of the polymer can be obtained numerically. In this paper, the effect of the spring coefficient on the drag-reduction is studied in detail. The quantitative relations between the drag-reduction rate and viscoelastic and Reynolds shear stress, etc., are obtained. Discussions are performed to clarify the relation between the turbulent structure of the polymer drag-reducing flow and the spring coefficient of the discrete-element model.