(590d) Type B Drag Reduction Fundamentals

Virk, P. S., Massachusetts Institute of Technology
Turbulent drag reduction is bounded by the Newtonian Prandtl-Karman law (PK) and an additive-independent asymptote of Maximum Drag Reduction (MDR). In the “polymeric regime” between PK and MDR, additives exhibit two distinct friction factor trajectories; namely (i) Type A, characteristic of initially randomly-coiling macromolecules, such as polyethyleneoxide PEO in water, and (ii) Type B, characteristic of extended macromolecules, such as partially hydrolysed polyacrylamide PAMH in deionized water, as well as a host of other polyelectrolytes in solvents of low ionic strength and many relatively rigid additives, including fibres, of paper, nylon and asbestos, clays and crystal sols. The present talk will examine some classic and current aspects of Type B drag reduction; namely (a) additive equivalence among A and B type trajectories, (b) drag reduction fall-off due to degradation, (c) an insensitivity to turbulence micro- and macro-scales, and (d) a two-state view of the drag reduction mechanism.