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的结构与非牛顿粘弹性流体流过该结构可能导致的弹性不稳定性之间的相互作用。人们已经对牛顿流体进行了大量的流体-结构相互作用(FSI)研究；然而，以前还没有对非牛顿流体进行粘弹性诱导的FSI研究。因此，从基础科学的角度全面了解这些粘弹性FSI现象，对于许多生物和工业应用都是非常重要的，可能会对FSI领域产生重大影响。对粘弹性流体和柔性结构之间的FSI有一个基本的了解，这对于改进碳纤维增强聚合物复合材料的制造技术具有很大的潜力，在碳纤维增强聚合物复合材料中，聚合物树脂通常是通过碳纤维簇驱动的。这项研究的结果将通过将建议的研究整合到K12学生和教师的扩展计划中并通过增加学生的研究机会来在不同的层面上传播。当柔性安装的钝体(如圆柱体)被放置在牛顿流动中时，在高雷诺数下分离的旋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)，并得到了广泛的研究。然而，如果将相同的柔性安装的圆柱体置于非牛顿流动中，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限小的雷诺数时可能变得不稳定。对于固定圆柱体周围的非牛顿流动，观察到了纯弹性流动不稳定性。研究将集中在柔性或柔性安装的结构对来自非牛顿流动的力的响应。这项研究将使用两种液体。对于蠕虫状胶束溶液，流动不稳定性发生在圆柱体的下游，而对于聚合物溶液，流动不稳定性发生在圆柱体的上游。为了将这些发现与几个重要的应用相联系，FSI测试将在微尺度上进行，通过考虑柔性水凝胶梁和聚合物溶液的力之间的相互作用来进行。在每一次试验中，将覆盖大范围的水流速度，在流动不稳定之前和之后，并将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，将采用测速仪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.