Influence of viscoelasticity in the flow on 1DOF and 2DOF vortex-induced vibrations of a cylinder*

We perform CFD simulations to study vortex-induced vibrations (VIV) of a cylinder in the inertial-elastic flow at a Reynolds number of Re = 100 and for a range of Weissenberg numbers of 0 < Wi < 10. In this range of Reynolds and Weissenberg numbers, both inertia and elasticity of the flow must be considered when it interacts with a flexibly-mounted cylinder. We use the FENE-P model to describe the viscoelastic fluid and investigate the effects of the Weissenberg number and the maximum polymer extensibility on the response of a flexibly-mounted cylinder with one or two degrees of freedom placed in flow. In addition to the primary vortices, we observe secondary vortices in the wake that are formed due to viscoelasticity in the flow. For increased elasticity in the fluid, we observe significant polymer deformation in the upstream stagnation region resulting in a region of large elastic stress that acts as a wall around the cylinder. As a result, the stagnation point moves upstream of the cylinder creating a finite gap between the shear layers and the cylinder surface. The region of flow separation is both widened and extended further downstream. With increased elasticity, VIV is suppressed in both one- and two-degree-of-freedom cases. We show that higher harmonic forces that are typically observed for the two-degree-of-freedom VIV responses in a Newtonian flow and cause increased fatigue damage in the structure, are suppressed by adding elasticity to the flow.