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

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

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.