Suppression of Flow-Induced Oscillations through the Addition of Viscoelasticity to the Fluid Flow

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In many examples of fluid-structure interactions, such as flow past underwater risers and mooring lines on offshore floating wind turbines and platforms, the turbulent effects of high-speed flow can cause oscillations that damage the structures. Minimizing these oscillations can reduce manufacturing and maintenance costs and increase the lifetime of such structures. While prior studies have examined this problem for Newtonian fluids (i.e., fluids with constant viscosity), this project will examine the effect non-Newtonian fluid properties, such as shear-thinning, shear-thickening, and viscoelasticity, on fluid-structure interactions. The investigators will test the hypothesis that increasing the viscoelasticity of the fluid can result in a reduction in the oscillation amplitude of a flexible structure. The findings of this research will be disseminated at different levels by integrating the proposed research into the outreach programs for K-12 students and teachers, by incorporating this research into undergraduate and graduate classes that the investigators teach, and by increasing research opportunities for both undergraduate and graduate students.This research will investigate through both detailed experiments and comprehensive numerical simulations the impact that non-Newtonian fluid properties have on fluid-structure interaction (FSI) at high Reynolds number (Re). Recent observations of FSI phenomena at infinitesimal Re, but high Weissenberg (Wi) numbers, where a viscoelastic fluid is in contact with a flexible or flexibly-mounted structure have shown that FSI phenomena at this low-Re, high-Wi space are different from those observed at high-Re, low-Wi space. One of the main differences is that the shedding of vortices that is the main cause of several high-Re FSI phenomena is not always observed in low-Re, high-Wi cases. The question arises then on how the increase in fluid elasticity will influence the shedding of vortices (and therefore the observed oscillations) of a high-Re FSI system. This research will investigate this fundamental question by systematically increasing the elasticity of an initially Newtonian fluid and observing the response of a flexibly-mounted structure in cross flow. Experiments and simulations are used to first study the response of a flexibly-mounted structure to the cross flow of shear-thinning and shear-thickening fluids followed by the addition of a high molecular weight polymer to a Newtonian fluid to make the fluid elastic. By investigating shear thinning, shear thickening, and elasticity separately, the research will independently determine the effect of each of them on the response of FSI systems. Finally, the fundamental knowledge gained from the first part of this work will be used to develop techniques that utilize the fluid viscoelasticity to fully suppress vortex induced vibrations. This will be accomplished through the localized injection of viscoelastic fluid directly into the boundary layer surrounding an oscillating structure.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.