Suppression of vortex-induced vibration of a circular cylinder using a pair of jets near the free surface

In practical engineering applications, Vortex-Induced Vibration (VIV) poses significant hazards to objects. Objects located near the free surface, such as those on a water platform, will also be affected by VIV. Therefore, the suppression of cylindrical vibration near the free surface should be paid more attention. In this paper, the effect of a pair of jets on cylinder vibration suppression near free surface is studied on the basis of two-dimensional model. To investigate the suppression effect of jet flows on the vibration of cylinders at different submerged depths near the free surface, four different submerged depth ratios (H^* = 1, 2, 3, and 10) were studied, and a group of bare cylinders with submerged depth ratio H^* = 2 was used for comparative analysis. The control effect of a couple of the jets on the cylinder increases as the submergence depth ratio decreases in the upper branch and lower branch. The motion response has changed from VIV to galloping in the lower branch. The flow is influenced by the narrow gap between the controlled cylinder and the free surface when it is close to the free surface, and a high-pressure area will be generated above the cylinder to suppress the vibration. Simultaneously, the presence of the jet disrupts the vortices forming on the rear side of the cylinder, thereby achieving the purpose of suppressing cylinder vibration. Furthermore, near the free surface, the presence of the jet alters the vortex structure, which also contributes to suppressing cylinder vibration.