On the link between experimentally-measured turbulence quantities and polymer-induced drag reduction in pipe flows

In this study, we investigate the hydrodynamics of polymer-induced drag reduction (DR) in horizontal turbulent pipe flows. We provide spatiotemporally resolved information of velocity and its gradients obtained with particle image velocimetry measurements in solutions of water with dissolved polyethylene oxide of three different molecular weights (MWs), at various dilute concentrations and with flow Reynolds numbers from 35,000 to 210,000. We find that the local magnitudes of important turbulent flow variables correlate with the measured levels of DR irrespective of the flow Reynolds number, polymer weight, and concentration. Contour maps illustrate the spatial characteristics of this correlation. A relationship between the DR and the turbulent flow variables is found. The effects of the polymer MW, its concentration, and the Reynolds number on the flow are further examined through joint probability distributions of the fluctuations of the streamwise and spanwise velocity components.