Effect of varying fluid rheology on viscoelastic fluid-structure interactions between a flexible cylinder and wormlike micelle solution

It is well known that when a flexible or flexibly-mounted structure is placed perpendicular to a Newtonian fluid flow, it can oscillate due to the shedding of vortices at high Reynolds numbers. Unlike Newtonian fluids, viscoelastic fluid flow can become unstable even at infinitesimal Re due to a purely elastic flow instability occurring at large Weissenberg numbers. We have recently shown that elastic flow instabilities can drive the motion of different flexible structures including sheets and cylinders. The fluctuating fluid forces exerted on the structures from the elastic flow instabilities can grow large enough to result in significant motion of the flexible structure, characterized into periodic 1D and 2D oscillations. In this talk, we present an investigation into the effects of varying fluid viscosity and relaxation time on the oscillatory response of the flexible structure, in terms of the elastic Mach number, in order to distinguish the complex flow instabilities observed during the 1D and 2D oscillations. The occurrence of the oscillations of a flexibly mounted, rigid cylinder at a frequency comparable to the structural natural frequency will be studied to further investigate the possibility of a window of lock-in behavior for viscoelastic fluid-structure interactions.