Vortex-induced vibration suppression of a main circular cylinder with two rotating control rods in its near wake: Effect of the rotation direction

Rotating small control rods in the near wake of a circular cylinder is a combination of both passive and active control techniques. The effect of rotation direction of control rods on vortex-induced vibration (VIV) suppression is investigated numerically by computational fluid dynamics (CFD) models coupling with a fluid-structure interaction (FSI) computational method. Two small rods with diameter ratio of 0.06 are located symmetrically at 135°right behind the main cylinder, and the gap between the main cylinder and control rods is 0.09D. The Reynolds number and the reduced velocity are 3484 and 6.0, respectively. Five different rotation modes are considered including the no-rotating case. The results indicate that the presence of control rods changes the momentum and kinetic energy distribution. Placing stationary rods in this specific position can achieve a good suppression effect, and the effect is enhanced when the control rods are inward counter rotating. Inward counter-rotating rods facilitate the momentum injection from the outer flow into the boundary layer, resulting in the delay of boundary layer separation and the shift of separation point. Therefore, the wake becomes narrower. However, control rods rotating outwardly play a counterproductive role in flow control and the vibration is enhanced. Rotating rods upwardly and downwardly have almost the same vibration responses. The cross-flow vibration is suppressed while the in-line vibration is enhanced at these two mirrored cases.