Polymer drag reduction is investigated using the Particle Image Velocimetry (PIV) technique in fully developed turbulent flow through a horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The polymer used was a commercially available partially hydrolyzed polyacrylamide (PHPA). The polymer concentration was varied from 0.07 to 0.12% V/V. The drag reduction is enhanced by increasing polymer concentration until the concentration reaches an optimum value. After that, the drag reduction is decreased with the increasing polymer concentration. Optimum concentration value of PHPA was found to be around 0.1% V/V. Experiments were conducted at solvent Reynolds numbers of 38700, 46700 and 56400. The percent drag reduction was found to be increasing with the increasing Reynolds number.
The study was also focused on analyzing the mean flow and turbulence statistics for fully-turbulent flow using the velocity measurements acquired by PIV. Axial mean velocity profile was found to be following the universal wall law close to the wall (i.e., y+ <10), but it deviated from log law results with an increased slope in the logarithmic zone (i.e., y+ >30). In all cases of polymer application, the viscous sublayer (i.e., y+ <10) thickness was found to be higher than that of the water flow. Reynolds shear stress in the core flow region was found to be decreasing with the increase in polymer concentration.
A particle image velocimetry study of dual-rotor counter-rotating wind turbine near wake
