471492 Why Fibers Are Better Turbulent Drag Reducing Agents Than Polymers
In this study , using hybrid Direct Numerical Simulation with Langevin dynamics, a comparison is performed between polymer and fiber stress tensors in turbulent flow. The stress tensors are found to be similar, suggesting a common drag reducing mechanism in the onset regime for both flexible polymers and rigid fibers. Since fibers do not have an elastic backbone, this must be a viscous effect. Analysis of the viscosity tensor reveals that all terms are negligible, except the off-diagonal shear viscosity associated with rotation. Based on this analysis, we are able to explain why polyelectrolytes in distilled water (i.e fibers) are better drag reducing agents than polyelectrolytes in salt water (polymer coils). Additionally, we identify the rotational orientation time as the unifying time scale setting a new time criterion for drag reduction by both flexible polymers and rigid fibers.
 P.S. Virk (1975), "Drag reduction by collapsed and extended polyelectrolytes", Nature, 253, 109-110
 A.M.P. Boelens, M. Muthukumar (Forthcoming) "Rotational relaxation time as unifying time scale for polymer and fiber drag reduction", PRE