Professors Yahya Modarres-Sadeghi (Principal Investigator) and Jonathan Rothstein (Co-Principal Investigator) have been awarded a $461,774 grant from the National Science Foundation’s Division of Chemistry, Bioengineering, Environmental and Transport Systems (CBET). The proposal, titled “Fluid-structure interactions between non-Newtonian viscoelastic fluids and flexible cylinders,” plans 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.
The research has the potential for numerous practical applications involving Fluid-Structure Interactions (FSI), including improving manufacturing techniques used for certain carbon-fiber reinforced polymer composites.
Many FSI studies have been performed with Newtonian fluids; however, no viscoelasticity-induced FSI studies of non-Newtonian fluids have been performed previously.
As the proposal’s abstract explains, “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.”
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,” as the researchers note. “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 researchers also note that 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,” the abstract explains, “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.” (November 2017)