Control of vortex-induced vibration of a circular cylinder using a pair of air jets at low Reynolds number

A numerical investigation was conducted to assess the effectiveness of an active control method using a pair of air jets positioned at the two shoulders of a circular cylinder for vortex-induced vibration (VIV) suppression at a low Reynolds number of 100. Unlike the same-phase jet-control technique, air injection leads to gas-liquid two-phase flow in the wake of cylinder. The ejected air is wrapped by the shear layer, and an air vortex is generated after the curled jet flow attains a certain length, corresponding to the consumption of ejecting energy. Then, air bubbles are formed and convected downstream with the shed vortices. The air vortices and bubbles interrupt the development of boundary layer and naturally shedding vortices, effectively delaying the vortex formation and hence the VIV suppression. The migration of air bubbles in the flow wake are categorized into two modes. One is bubbles coinciding with vortices and convecting downstream with them. The other is bubbles deviating from the center of vortices but continually interrupting the vortices by drawing the ambient vorticity-carrying fluid. The vibration control becomes more effective with the increase of momentum coefficient. After implementing air-jet control at Ujet/Uin = 2, more than 60% reduction in transverse amplitude is achieved.