Polymer-dominant drag reduction in turbulent channel flow over a superhydrophobic surface

Abstract

In this study, we focused on the integration of a flexible polymer (polyacrylamide) and a (randomly patterned) superhydrophobic surface in a large-scale turbulent channel flow rig to investigate their combined drag reduction effectiveness. Experimental results indicate that, prior to degradation, polyacrylamide (at a 100-ppm concentration) and superhydrophobic surfaces individually manifest drag reductions of 35% and 7%, respectively. However, when combined, the influence of polymer additives remained consistent, with the introduction of superhydrophobic surfaces yielding negligible differences. A clear predominance was evidenced in our facility looking at realistic pressure for applications, with polymer additives overshadowing the impact of superhydrophobic surfaces.