A Theory of Drag Reduction in Pipe Flows by Polymer Additives
Abstract
Addition of modest amounts of polymer solution has long been known to reduce drag in turbulent pipe flows. The observations that a critical polymer relaxation rate is required for drag reduction, and that drag reduction is accompanied by decorrelation of cross-stream and along-stream velocities but not by drastic reductions in turbulence levels suggest that the polymer drag reduction phenomenon may be interpreted as one of formation of a momentum transport barrier adjacent to the viscous sub-layer. This scenario closely resembles that of the L arrow H transition in tokamaks. A coupled set of equations for the fluid dynamics (including polymer-induced back-reaction) and for the (tensor) polymer extension field has been derived. This system closely resembles the familiar equations of MHD. Drag reduction occurs due to the cancellation of fluid Reynolds and polymer elastic stresses in the region where the polymer is ``activated'' by eddy strain.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- November 1997
- Bibcode:
- 1997APS..DPPpTP126L