Suppression of vortex-induced vibration of an elastically mounted sphere by electromagnetic force.

In this paper, electromagnetic force on two degrees of freedom vortex-induced vibration (VIV) of an elastically mounted sphere for vibration suppression is numerically achieved at Re = 300. The relations between the wake structures, velocity and pressure distributions, force coefficients, and sphere displacement are investigated by varying the interaction parameter (N) of electromagnetic force. With the increase in N, the momentum of the fluid near the sphere is enhanced to control the flow separation. Therefore, both the rotation radii of the rear stagnation point (RSP) and the separation line (SL) decrease, causing the spiral vortices to become thinner. This leads to a reduction in the fluctuation amplitude of the lift coefficient and mitigates the VIV. As N exceeds 0.5, the periodic spiral vortices transform into a steady double-thread wake due to the stopping of RSP and SL rotation. Therefore, a constant lift is generated in the z-direction due to the asymmetric flow field in the x–z plane, which is accompanied by the VIV fully suppressed. Moreover, the effect of electromagnetic locations (θ_m) on vibration suppression is examined. With the increase of θ_m, the vibration suppression efficiency increases first and then decreases, which achieves the maximum vibration suppression efficiency at θ_m = 125°. The reason is that the electromagnetic force covers the location of the half-circle-shaped SL, which has a significant effect on the control of the flow separation. [ABSTRACT FROM AUTHOR]