Fluid-structure interactions between non-Newtonian viscoelastic fluids and flexible cylinders

拟议研究的目标是研究柔性或柔性安装结构与非牛顿粘弹性流体流过该结构时可能产生的弹性不稳定性之间发生的相互作用。许多流体-结构相互作用（FSI）研究都是用牛顿流体进行的；然而，之前还没有对非牛顿流体进行粘弹性诱导的FSI研究。因此，从基础科学的角度来看，对这些微弹性FSI现象的全面理解不仅是有趣的，而且对于许多生物和工业应用都是必不可少的，具有改变FSI领域的潜力。对粘弹性流体和柔性结构之间的FSI的基本理解，对于改进碳纤维增强聚合物复合材料的制造技术具有巨大的潜力，这种复合材料通常是通过碳纤维簇驱动聚合物树脂。本研究的结果将通过将建议的研究整合到K12学生和教师的外展计划中，并通过增加学生的研究机会，在不同层次上传播。当柔性钝体（如圆柱）置于牛顿流中时，高雷诺数下分离涡的脱落可以驱动结构的运动。这种现象被称为涡激振动（VIV），已经得到了广泛的研究。然而，如果将相同的柔性圆柱体置于非牛顿流中，则结构的响应是未知的。与牛顿流体不同，粘弹性流体的流动在无穷小的雷诺数下会变得不稳定。对于绕固定圆柱的非牛顿流动，已经观察到纯弹性流动的不稳定性。该研究将集中于柔性或柔性安装结构对非牛顿流力的响应。研究中将使用两类液体。对于蠕虫状胶束溶液，流动不稳定发生在圆柱体的下游，而对于聚合物溶液，流动不稳定发生在圆柱体的上游。为了将这些发现与几个重要的应用联系起来，FSI测试将在微观尺度上进行，考虑柔性水凝胶梁和聚合物溶液的力之间的相互作用。在每次试验中，在流动失稳前和失稳后，将覆盖一个很宽的流速范围，并在每一步测量结构的位移。为了量化结构振荡对流动不稳定性的影响，将采用速度测量和流动诱导双折射测量。

The goal of the proposed research is to study the interactions that occur between a flexible or flexibly-mounted structure and the elastic instabilities that can result from the flow of a non-Newtonian viscoelastic fluid past that structure. A host of Fluid-Structure Interactions (FSI) studies have been performed with Newtonian fluids; however, no viscoelasticity-induced FSI studies of non-Newtonian fluids have been performed previously. As a result, a comprehensive understanding of these vicoelastic FSI phenomena is both intriguing from a fundamental scientific point of view and essential for a number of biological and industrial applications, with potentials of being transformative to the field of FSI. A fundamental understanding of FSI between viscoelastic fluids and flexible structures has great potentials for improving manufacturing techniques used for carbon fiber reinforced polymer composites where often a polymer resin is driven through a cluster of carbon fibers. The findings of this research will be disseminated at different levels by integrating the proposed research into the outreach programs for K12 students and teachers, and by increasing research opportunities for students.When a flexibly-mounted bluff body (such as a circular cylinder) is placed in Newtonian flows, the shedding of separated vortices at high Reynolds numbers can drive the motion of the structure. This phenomenon is known as Vortex-Induced Vibration (VIV) and has been studied extensively. If the same flexibly-mounted circular cylinder is placed in non-Newtonian flows, however, the structure's response is unknown. Unlike Newtonian fluids, the flow of viscoelastic fluids can become unstable at infinitesimal Reynolds numbers. For non-Newtonian flows around a fixed circular cylinder, purely elastic flow instabilities have been observed. The research will focus on the response of flexible or flexibly-mounted structures to forces from non-Newtonian flows. Two classes of fluids will be used in the study. For wormlike micelle solutions, the flow instabilities occur downstream of the cylinder, and for polymer solutions the flow instabilities occur upstream of the cylinder. To relate the findings to several important applications, FSI tests will be conducted at a micro scale by considering the interactions between flexible hydrogel beams and the forces of polymer solutions. In each test, a wide range of flow velocities will be covered, before and after the flow instability, and the structure's displacement will be measured at each step. Velocimetry and flow-induced birefringence measurements will be taken in order to quantify the influence of the structural oscillations on the flow instabilities.