75th Annual Meeting of the APS Division of Fluid Dynamics (November 20, 2022 — November 22, 2022)

V0087: Mode-A? Mode-B? Naaahh, 2-DOF VIV loves Mode-C !!

Authors

• Mayank Verma, Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, India
• Ashoke De, Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, India

DOI: https://doi.org/10.1103/APS.DFD.2022.GFM.V0087

The present video investigates the three-dimensionality of the wake behind a circular cylinder oscillating under the 2-degree-of-freedom vortex induced vibrations. The study finds that the oscillating cylinder (under 2-DOF VIV) sweeps a figure 'eight' trajectory and the motion of the cylinder alters the mode of three-dimensionality the wake follows for the transition from fully two-dimensional wake to the three-dimensional wake. The spanwise vortices have been identified using the iso-surfaces of the negative value of the second eigenvalue (λ₂) of the tensor S² + Ω², where S and Ω are the symmetric and antisymmetric parts of the velocity gradient tensor ▽u. The spanwise wavelength (λ_z) of the vortices reveals that the cylinder under 2-DOF VIV system follows mode-C instability (with λ_z = 1.92) for the transition from 2D to 3D wake instead of mode-B (with λ_z = 0.90) transition observed in the 1-DOF VIV system or the mode-A (with λ_z = 3-5) observed for the stationar cylinder.