Vortex-Induced Vibrations of Tapered cylinder

We have performed the three-dimensional numerical simulations employing the open-source Finite Volume-based solver of OpenFOAM. In the simulations, the 2-DOF VIV system (modelled as the spring-damper equations) allows the movement of the tapered cylinder in both the inline and cross-flow directions. The cylinder is 9.6 times the averaged cylinder diameter (D=(d₁+d₂)/2, where d₁ and d₂ are the largest and smallest diameter of the tapered cylinder) in length (l) and corresponds to a low mass ratio of m* = 10. The simulations are performed over taper ratios (defined as τ=l/(d₂-d₁) : 10, 20, and 40) for a range of reduced velocities (3≥U_r≥12). The findings indicate that increasing the taper ratio leads to delayed branch change between the initial to lower branch. Additionally, the peak amplitude of the oscillations is lower compared to the uniform cylinder, and this occurs at a significantly higher reduced velocity. The vorticity contours display the presence of oblique vortex shedding downstream of the tapered cylinder, contributing to the formation of cellular vortex shedding when higher taper ratios are employed.