On two distinct types of drag-reducing fluids, diameter scaling, and turbulent profiles

Two distinct scaling procedures were found to predict the diameter effect f or different types of drag-reducing fluids. The first one, which correlates the relative drag reduction (DR) with flow bulk velocity (V), appears appl icable to fluids that comply with the 3-layers velocity profile model. This model has been applied to many polymer solutions: but the drag reduction v ersus V scaling procedure was successfully tested here for some surfactant solutions as well. This feature, together with our temperature profile meas urements, suggest that these surfactant solutions may also show this type o f 3-layers velocity profiles (3L-type fluids). The second scaling procedure is based on a correlation of tau (w) versus V, which is found to be applicable to some surfactant solutions but appears t o be applicable to some polymer solutions as well. The distinction between the two procedures is therefore not simply one between polymer and surfacta nts. It was also seen that the tau (w) versus V correlation applies to flui ds which show a stronger diameter effect than those scaling with the other procedure. Moreover, for fluids that scale according to the tau (w) versus V procedure, the drag-reducing effects extend throughout the whole pipe cro ss section even at conditions close to the onset of drag reduction, in cont rast to the behavior of 3L fluids. This was shown by our measurements of te mperature profiles which exhibit a fan-type pattern for the tau (w) versus V fluids (F-type), unlike the 3-layers profile for the fluids well correlat ed by drag reduction versus V. Finally, mechanically-degraded polymer solut ions appeared to behave in a manner intermediate between the 3L and F fluid s. Furthermore, we also showed that a given fluid in a given pipe may transiti on from a Type A drag reduction at low Reynolds number to a Type B at high Reynolds number, the two types apparently being more representative of diff erent levels of fluid/flow interactions than of fundamentally different phe nomena of drag reduction. After transition to the non-asymptotic Type B reg ime, our results suggest that, without degradation, the friction becomes in dependent of pipe diameter and that the drag reduction level becomes also a pproximately independent of the Reynolds number, in a strong analogy to New tonian flow. (C) 2001 Elsevier Science B.V. All rights reserved.