Bulk Turbulence in Polymer Solutions: Beyond Friction Drag Reduction

Yale University, New Haven CT

Investigators

Abstract

PI: Ouellette, Nicholas Proposal Number: 1436423 The goal of the proposed research is to explore the effects of adding polymers in the bulk of turbulent flows. When small amounts of additives, including long-chain polymers, surfactants, or microbubbles, are added to a turbulent flow, the structure and dynamics of the flow can change dramatically. The most celebrated effect of additives is skin-friction drag reduction: tiny amounts of polymers or surfactants can reduce the drag in a turbulent wall-bounded flow by up to 80%. After years of research, the scientific community is beginning to reach consensus on the fundamental physics of this drag reduction. Skin friction, however, is only a part of the total fluid drag experienced by ships or other objects immersed in a fluid. Separation of the boundary layer and the dynamics of turbulent wakes lead to energy losses that frequently dominate the frictional losses over the object. Understanding how additives affect these other types of drag requires the study of the modification of bulk turbulence, far from any walls, in the presence of additives. Although it is known that bulk turbulence does change with additives, current models cannot explain the experimental observations. The research proposed here will address this gap via detailed experimental measurements of bulk turbulence in polymer solutions. In terms of education and outreach, a new module for an undergraduate laboratory class based on non-Newtonian turbulence, will be developed. In addition, the PI will develop movies about the research results that will be displayed in an on-campus coffee shop and on YouTube, and will participate in K-12 outreach via a local science-fair program. The primary goal of the project is to understand what aspects of the modification of the turbulent dynamics by polymers is dependent on the presence of a wall, and what aspects are more universal. To address this question, the rates of energy injection, scale-to-scale transfer, and dissipation will be measured as a function of polymer concentration, and modification to the decay of turbulence will be studied. In addition, measurements will be made of the spatial structure of the flow, in order to test the common hypothesis that polymers interact with and suppress small-scale vorticity. The experimental measurements will be made in the Lagrangian framework, using Lagrangian particle tracking, where a multicamera stereoimaging setup is used to follow the motion of small tracer particles in three dimensions and in time as they are advected by the flow.