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

在许多流体-结构相互作用的例子中，例如流过海上浮式风力涡轮机和平台上的水下隔水管和系泊线的水流，高速水流的湍流效应会引起振荡，从而破坏结构。最小化这些振荡可以降低制造和维护成本，并增加这种结构的使用寿命。虽然先前的研究已经对牛顿流体（即具有恒定粘度的流体）进行了研究，但本项目将研究非牛顿流体性质（如剪切变薄、剪切增稠和粘弹性）对流固相互作用的影响。研究人员将测试这样一个假设，即增加流体的粘弹性可以导致柔性结构的振荡幅度减小。本研究的结果将通过将拟议的研究整合到K-12学生和教师的外展计划中，通过将本研究纳入研究者教授的本科和研究生课程中，以及通过增加本科生和研究生的研究机会，在不同层次上传播。本研究将通过详细的实验和全面的数值模拟来研究非牛顿流体性质对高雷诺数（Re）下流固相互作用（FSI）的影响。最近对无限小Re，但高Weissenberg （Wi）数的FSI现象的观察表明，粘弹性流体与柔性或柔性安装结构接触时，这种低Re，高Wi空间的FSI现象与高Re，低Wi空间的FSI现象不同。其中一个主要的区别是，在低re、高wi的情况下，并不总是观察到一些高re FSI现象的主要原因涡的脱落。接下来的问题是，流体弹性的增加将如何影响高re FSI系统的涡流脱落（从而影响观察到的振荡）。本研究将通过系统地增加初始牛顿流体的弹性并观察柔性安装结构在横流中的响应来研究这个基本问题。首先通过实验和模拟研究了柔性安装结构对剪切减薄和剪切增稠流体交叉流动的响应，然后在牛顿流体中加入高分子量聚合物以使流体具有弹性。通过分别研究剪切变薄、剪切变厚和弹性，研究将独立确定它们对FSI系统响应的影响。最后，从本工作的第一部分中获得的基本知识将用于开发利用流体粘弹性来完全抑制涡激振动的技术。这将通过将粘弹性流体直接局部注入振动结构周围的边界层来实现。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.