Polymers and Plastrons in Parallel Yield Enhanced Turbulent Drag Reduction

Anoop Rajappan,Gareth H. McKinley

doi:10.3390/fluids5040197

Anoop Rajappan, Gareth H. McKinley

Open Access

https://doi.org/10.3390/fluids5040197

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Abstract

Despite polymer additives and superhydrophobic walls being well known as stand-alone methods for frictional drag reduction in turbulent flows, the possibility of employing them simultaneously in an additive fashion has remained essentially unexplored. Through experimental friction measurements in turbulent Taylor–Couette flow, we show that the two techniques may indeed be combined favorably to generate enhanced levels of frictional drag reduction in wall-bounded turbulence. We further propose an additive expression in Prandtl–von Kármán variables that enables us to quantitatively estimate the magnitude of this cooperative drag reduction effect for small concentrations of dissolved polymer.

Highlights

Wall-bounded turbulent flows play a ubiquitous role in modern engineering and industry, in applications ranging from the internal flow of liquids in pipelines, to the external boundary layer flow around the hulls of ships and submarines [1,2]
The addition of soluble, high molar mass polymers has long been known to be an effective strategy for reducing frictional drag in turbulent flows [14,15,16]
Results are organized into four sections based on the working fluid inside the gap, and the flow boundary condition at the rotor surface

Summary

Introduction

Wall-bounded turbulent flows play a ubiquitous role in modern engineering and industry, in applications ranging from the internal flow of liquids in pipelines, to the external boundary layer flow around the hulls of ships and submarines [1,2]. The systematic modification of turbulence dynamics through the introduction of either dissolved polymer chains [3,4,5,6,7] or boundary slip [8,9,10], leading to drag reduction, remains an active area of research and has witnessed resurgent interest in recent years [11,12,13]. The addition of soluble, high molar mass polymers has long been known to be an effective strategy for reducing frictional drag in turbulent flows [14,15,16]. A wide range of synthetic as well as naturally occurring high polymers have been successfully employed as drag reducing agents in a variety of turbulent flow configurations [17,18]

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Results

Conclusion