On the turbulent drag reduction in viscoelastic flows: effects of elasticity number and polymer characteristics

The effects of introducing small amounts of flexible long-chain polymers to a Newtonian liquid have been well-studied since the discoveries of Toms in 1948 for a pipe flow. In some cases, friction drag can be reduced up to 80%, making polymer additives a promising drag-reducing technique in industrial pipe flow systems. In practice, studying the effect of the elasticity number (El) becomes challenging since changing El (which is independent of the velocity) constitutes changing the fluid properties or flow geometry. In this study, direct numerical simulations of viscoelastic flows using the FENE-P model are performed. Dimensionless parameters such as Reynolds number (Re) and Weissenberg number (Wi), and polymer characteristics are evaluated for the effects of El = Wi/Re. The preliminary results show that for the low-El regime studied, higher drag reduction (DR) is achieved for increasing Wi at a constant Re. Furthermore, increasing polymer concentration increases DR due to a resulting increase in Wi, but the magnitude of DR increase between polymer concentrations appears to depend on Re. The effects of other polymer characteristics will be further discussed.