Numerical investigation of enhanced vortex induced vibration energy harvesting of a circular cylinder using a rotating control rod

This study investigates the influence of an upstream rotating control rod on the vortex-induced vibration energy harvesting of a circular cylinder at Reynolds number 10 000, using a combination of a modified direct forcing immersed boundary and a large eddy simulation technique. Specifically, we analyze the effects of the control rod rotation rate, the gap ratio, and the damping ratio on cylinder response, hydrodynamic forces, wake dynamics, and energy harvesting efficiency. The results show that the rotating control rod significantly modifies wake and enhances the vibration response in a wide range of reduced velocity. The optimum energy extraction efficiency occurs at a control rod rotation rate of 1 and a gap ratio of 0.2, achieving a harvesting efficiency of 43%, an improvement of approximately 15% over the passive case, and double the efficiency of a bare cylinder. Moderate control rod rotation promotes coherent vortex shedding and maximizes oscillation amplitude and fluid to structure energy transfer, while higher rotation rates destabilize the wake and reduce energy harvesting performance. Although very low damping produces the highest oscillation amplitudes, the highest harvesting efficiency is obtained at a moderate damping ratio of 0.025–0.05, indicating an optimal balance between vibration response and energy extraction. In general, the upstream rotating control rod greatly enhances vibration response and energy harvesting by manipulating wake interaction and broadening the lock-in region.