The enhancement of flow induced vibration of a circular cylinder using a rotating control rod

The enhancement of flow induced vibration of a circular cylinder by a rotating control rod is investigated through two-dimensional numerical simulations. The Reynolds number, diameter ratio, and gap ratio are 150, 0.2, and 0.2, respectively. Simulations are conducted for two rod position angles of β = 90° and 135°, rotation rates ranging from 0 to 6, and reduced velocities ranging between 1 and 20. The response of the cylinder–rod system at the rotation rates 0 and 1 has a lock-in regime where the vibration amplitude is high and the vibration frequency stops increasing with the increase in reduced velocity linearly. For rotation rates exceeding 2, the response amplitude increases with the increase in reduced velocity and enters the lock-in regime at the lower boundary reduced velocity. It remains high until the largest studied reduced velocity of 20; as a result, the higher boundary reduced velocity of the lock-in regime cannot be determined. The vibration with large amplitudes and large rotation rates repeats cyclically after every two or more vibration periods. As a result, two combined wake modes are found: 2S/P + S and 2P/P + S. In a combined mode, the vibration changes from one mode to another within each cycle. The cylinder receives power from the fluid, and the rotating rod gives power to the fluid although the net power exchange between the whole system and the fluid is zero.