NUMERICAL INVESTIGATIONS OF ADAPTIVE VORTEX-INDUCED VIBRATION SUPPRESSION OF A WAVY CYLINDER

By employing large eddy simulation (LES) and overset mesh, the vortex-induced vibration (VIV) mechanism of a wavy cylinder, with the suction control at the azimuthal angles of 90°/270° and 120°/240°, has been numerically investigated for the reduced velocities U_r from 2.4 to 13.2. In addition, to suppress the vibration by an adaptive suction control, the velocity information is monitored in real-time and serves as feedback in the reinforcement learning (RL) framework. With the optimization goals of reducing the amplitude of VIV and minimizing energy input, the proximal policy optimization (PPO) algorithm is employed to adjust the momentum coefficient of suction. The result indicates that the lock-in range narrows significantly with the suction control, but the threshold wind speed at which the cylinder begins to vibrate advances. Under the suction control, the shear layer is extended in the streamwise direction, and the vortex shedding mode is transformed into a parallel shedding mode characterized by elongated tail vortices. These changes reduce the negative pressure on the leeward side of the cylinder and suppress the pulsating excitation of the vortex-induced vibration. The vibration suppression effect is better when the suction control is applied at the azimuthal angles of 120°/240°. The amplitude ratio at the peak is reduced by about 73.17% compared to the uncontrolled condition. The adaptive control process shows that the higher momentum inflow than the open-loop control is taken firstly to quickly decrease the vibration amplitude, and then a lower momentum inflow is utilized to maintain the low amplitude state. Compared to the uncontrolled condition, the amplitude ratio is reduced by approximately 96.9% with a lower momentum inflow than the open-loop control. The research result has achieved adaptive closed-loop vibration suppression control of the wavy cylinder, providing new insights and approaches for the adaptive active control of flow around bluff bodies.