The transformation mechanisms of vortex structures on vortex-induced vibration of an elastically mounted sphere by Lorentz force

Abstract

The transformation mechanisms of vortex structures on vortex-induced vibration (VIV) of an elastically mounted sphere by Lorentz force are numerically investigated at Re = 300. The relations among the sphere trajectories, wake structures, vorticity distribution, and the rotation characteristics of the rear stagnation point (RSP) and separation line (SL) are discussed before and after the application of Lorentz force . From this, the transformation mechanisms of vortex structures on sphere VIV are revealed. The sphere, when released, initially begins to vibrate along a linear path in the transverse plane and then transforms smoothly into a circular path, which leads to the transition from hairpin vortices to spiral vortices. After the application of Lorentz force , the fluid near the sphere is accelerated. The rotations of the RSP and SL are fully suppressed, which leads to the transition from the spiral vortices to the double-thread wake. Moreover, the wake structures vary with the interaction parameter N of the Lorentz force. The spiral vortices arise for small values of N , where the vibration magnitude grows for N = -0.2 and decays for N = 0.2. When N is increased to 1, the vibration of the sphere is fully suppressed. Therefore, the spiral vortices are replaced by the steady double-thread wake.