Active turbulence from polymer additives: Theory, modeling and high fidelity simulations

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Complex fluids define a wide variety of fluids encountered in pharmaceutical, food, petroleum, biological industries. The manner in which many of these fluids flow challenges the predictive models currently used by engineers and scientists for the design and optimization of engineering applications and understanding of physical phenomena. For instance, the addition of polymers in a liquid, the complex fluid of interest here, can reduce drag when transporting water or oil in pipes, but also increase heat transfer and mixing in microfluidics. It can promote formation of emulsion between two immiscible solutions under conditions at which an emulsion is not otherwise possible, or it can control droplet sizes in spray to improve agricultural irrigation or combustion in liquid fuel injection engines. Polymer additives offer, and in some of the applications mentioned above, deliver large returns on investment, however the modeling or predictability of these phenomena remains poor owing to the absence of sound theoretical understanding. The main objective of this project is to develop high-fidelity predictive computational models that will benefit a large range of industries dealing with complex fluids. The project will also have an education component, encompassing training of a graduate student in complex fluid dynamics and numerical simulation, and the development of open-source tools used in turbulence and computational fluid dynamics courses.Polymer additives offer a unique window of investigation into complex energy transfers involving direct and inverse energy cascades between large and small scales, between turbulence and polymer molecules. Polymer additives have been identified as responsible for elastic turbulence in inertialess flows, elasto-inertial turbulence in subcritical wall-bounded flows and drag reduction in supercritical wall-bounded flows up to an asymptotic, non-laminar state called maximum drag reduction. None of these states are well understood. The objectives of the proposed research effort are to fully characterize the statistical properties of the above mentioned turbulent states, to investigate the energy transfer between polymers and flows in all turbulent states in search for universal properties and to leverage the cumulative sum of knowledge acquired within this project into high fidelity computational models of non-Newtonian turbulent flows at very low to large Reynolds numbers. The numerical simulations used to support this project are state-of-the-art viscoelastic direct numerical simulations developed to capture the targeted dynamics. This project will create a unique and extensive database of elastic and elasto-inertial turbulent flows which will be made available to the scientific community.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.