Numerical study on vortex-induced vibration responses of a circular cylinder attached by a free-to-rotate dartlike overlay

• VIV response of a cylinder with a free-to-rotate dartlike overlay is numerical studied.
• The overlay rotates counterclockwise under the drive of fluid flow.
• Effect of rotating overlay on VIV response is discussed.
• Overlay enhances VIV at large flow velocity.
• The critical velocity of VIV enhancement is obtained.

In the present paper, the two-degree-of-freedom vibration responses of a circular cylinder attached by a free-to-rotate dartlike overlay with Reynolds number ranging from 1715.9 to 6851.6 are modeled in two dimensions by using the commercial CFD code “Fluent”. The rotation of the dartlike overlay can disturb the flow around the cylinder and simultaneously convert hydrokinetic energy to mechanical energy. The URANS equations and SST k-ω turbulence model are employed to calculate the flow field, while a fourth-order Runge–Kutta method is applied to evaluate the motion of the system. It is found that the overlay rotates counterclockwise under the drive of fluid flow, resulting in 2S wake mode throughout the reduced velocity range. The boundary layer separation points move to the four tips of the overlay. Due to the shearing action of rotating overlay, small vortices are cut off from the vortices shedding from overlay tips. The rotation of overlay speeds up the migration of the vortices to the downstream. However, as the reduced velocity is larger than 6.7, the vibration of the system is enhanced. So this free-to-rate overlay can be used as power generation device at high reduced velocity.