Saturation of turbulent drag reduction in dilute polymer solutionsR. Benzi1, V. S. L'vov2, I. Procaccia2 and V. Tiberkevich2
1 Dipartimento di Fisica and INFM, Università "Tor Vergata" Via della Ricerca Scientifica 1, I-00133 Roma, Italy
2 Department of Chemical Physics, The Weizmann Institute of Science Rehovot, 76100 Israel
received 15 June 2004; accepted in final form 15 October 2004
published online 17 November 2004
Drag reduction by polymers in turbulent wall-bounded flows exhibits universal and non-universal aspects. The universal maximal mean-velocity profile was explained in a recent theory. The saturation of this profile and the crossover back to the Newtonian plug are non-universal, depending on Reynolds number , concentration of polymer and the degree of polymerization . We explain the mechanism of saturation stemming from the finiteness of extensibility of the polymers, predict its dependence on and N in the limit of small and large , and present the excellent comparison of our predictions to experiments on drag reduction by DNA.
47.27.-i - Turbulent flows, convection, and heat transfer.
47.27.Ak - Fundamentals.
47.27.Nz - Boundary layer and shear turbulence.
© EDP Sciences 2004