Structure and mechanism of elastoinertial turbulence in polymer and surfactant solutions

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Adding large polymer molecules to a liquid can lead to a substantial reduction of energy losses in the turbulent flow regime, which is characteristic of many flows in nature and technology. A similar effect arises in solutions containing certain surfactant (detergent-like) molecules. These additives give a liquid an elastic character that is absent in simple liquids like water. The phenomenon is used to improve energy efficiency in flow processes ranging from oil pipelines to geothermal district heating operations, but the mechanisms underlying it remain poorly understood. This project will reveal universal features of the flow structures underlying this drag reduction effect by using computational fluid dynamics simulations in multiple geometries. The outcome will advance the understanding of turbulence in viscoelastic fluids encompassing both polymer and surfactant solutions, enabling the design of fluids and flow processes that decrease energy consumption. The research team will partner with the UW-Madison Institute for Chemical Education to provide educational opportunities. Undergraduate engineering students will develop project-based lessons in fluid mechanics and present them at 4H, Wisconsin Science Festival, Engineering Expo (UW-Madison College of Engineering outreach event), and local science nights at schools. Recent studies have revealed two regimes of near-wall turbulence in viscoelastic polymer solutions. In the first, turbulence is sustained by quasi-streamwise vortices. As viscoelasticity becomes more important, the second regime emerges, where these vortices are suppressed and a new type of flow, denoted elasto-inertial turbulence, emerges. This project tests the hypothesis that elasto-inertial turbulence has universal structural and mechanistic features across parameter space and flow geometry. Direct simulations of turbulent dynamics in polymer solutions will be analyzed using an extension of Spectral Proper Orthogonal Decomposition appropriate to complex fluids. This work will be complemented by linear and weak-nonlinear analyses to reveal the mechanisms behind the nonlinear self-sustaining nature of elasto-inertial turbulence. Direct simulations and analysis will also be performed with a new model of viscoelastic surfactant solutions developed by the principal investigator’s group to understand whether universality in elasto-inertial turbulence extends to other complex fluids. This work will set the stage for studies of heat and mass transfer and whether elast-oinertial turbulence can be suppressed, leading to even further reductions in turbulent drag. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.