Influence of fluid elasticity on the flow-induced vibrations of a flexibly-mounted square prism

We numerically investigate how adding fluid elasticity affects the response of a flexibly mounted rigid square prism, with one degree-of-freedom, placed in fluid flow. The FENE-P (Finitely-Extensible Nonlinear Elastic) constitutive model is utilized to calculate the polymeric stress field. A two-way coupling scheme is implemented to simulate the interaction between the fluid flow and the mass-spring system. We test square prisms with two different mass ratios m^* = 2 and 20 under various reduced velocities between 3<U^*<45 and at a fixed Reynolds number of Re = 200. We set the fluid to have a viscosity ratio of β = 0.9, and a Weissenberg number of Wi = 2, which then yields an elastic number of El = 0.01. We show that even a small amount of fluid elasticity can affect the flow-induced instabilities significantly. Through the simulations, we observe an enhancement of galloping response on the prism as elasticity is added to the fluid compared with its response in Newtonian fluid, especially for the small mass ratio case, where the critical reduced velocity for galloping decreases dramatically and the oscillation amplitude increases significantly. Our results also show the suppression of vortex-induced vibrations by adding elasticity to the fluid. We discuss the mechanisms that lead to these phenomena based on visualizations of the flow field and analysis of flow forces.