Remarkable drag reduction in non-affine viscoelastic turbulent flows

We carry out a direct numerical simulation (DNS) study which aims to reveal the mechanism of turbulence drag reduction (DR) in polymer diluted flows. The polymer chains are modeled as elastic dumbbells. This paper focuses on elucidation of effect of introduction of non-affinity to describe the motions of the dumbbells on DR. We consider the cases in which the motions do not precisely correspond to macroscopically-imposed deformation. The Johnson-Segalman (JS) model is adopted to express the polymer stress. Assessment is done in forced homogeneous isotropic turbulence and pipe flow. In both flows, DR exhibits non-monotonous dependence on the strength of non-affinity. DR is maximal when non-affinity is either minimum (slip parameter α = 0.0) or maximum (α = 1.0) and almost no DR is obtained when α = 0.5. Remarkable enhancement of DR is achieved when α = 1.0 in both flows. In pipe flow, the mean velocity profile surpasses the Virk's maximum DR limit and nearly complete relaminarization occurs. This marked DR...