In order to understand the gap flow between two cylinders, the characteristics of flow around two stationary cylinders and the flow-induced vibration of two staggered cylinders with roughness strips are numerically studied. The lift-drag responses, Strouhal number (St) and wake structure of two stationary cylinders in tandem, as well as the vibration response and vortex pattern of two oscillating staggered cylinders are analyzed. The results indicate that the spacing d c of two stationary cylinders at which the gap flow can be observed is different for different Re, and d c is 3D when Re = 2000 and d c = 2.5D at Re = 6000~14,000. When the distance d = d c , the force coefficient and St of two cylinders increase sharply. For the two oscillating staggered cylinders, there is a critical reduced velocity U c * = 7, which makes the amplitude magnitude relationship of the two cylinders change. With the change of the reduced velocity, the vibration frequencies of the two cylinders are consistent. When the staggered distance increases, the frequency difference of the two cylinders decreases. At the same inflow velocity, with the increase of staggered distance, a gap flow is formed between the two cylinders. When T > 0.6D and U* < 8, the gap flow becomes the main factor affecting the vibration of the two cylinders, which can be divided into the dominant region of gap flow.The FIV of a bluff body is a very complicated fluid-solid coupling process. Many studies have been done in this field, mainly focusing on the FIV characteristics and vibration control of the bluff body. The representative reviews of FIV of cylinders are by Williamson [5] and Bearman [6]. The control of FIV is embodied in two aspects. On the one hand, it is the suppression of vibration. Canpolat [7] found that rectangular grooves on a cylinder can effectively control flow through PIV experiments. Feng [8] used a water tunnel experimentation study and found that a synthetic jet can significantly change the scale of eddy current and wake mode. Lam [9] discussed the flow around a corrugated cylinder by large eddy simulation and experiment, and they controlled the vibration of the tube bundle in a heat exchanger by adding a corrugated cylinder to the tube bundle array. Zhu [10] and Song [11] studied the inhibition effect of small control rods on vortex-induced vibration (VIV). The former compared the VIV characteristics under different rod numbers, diameter ratios and gap ratios. It was found that when the attachment had nine control rods, the diameter ratio was 0.15, and the clearance ratio was 0.6, the inhibition effect of VIV was the best. The latter simulated the VIV characteristics of a cylinder with three small control rods at different angles of attack and clearance ratios. It was found that the inhibition effect was the best when the angle of attack was 45 and the clearance ratio was 0.9. Wu et al. [12] found a new method to control VIV: A twisted cylinder, which was applied to a semi-submersible offshore platform. Compared with a square cylinder, the...

Flow-induced motions (FIM) of an elastically mounted circular cylinder with roughness strips at different angles of attack are investigated by 2-D URANS simulations based on the open source CFD tool OpenFOAM. The cylinder is constrained to one degree of freedom motion in the transverse direction. Two selectively distributed roughness strips on cylinder surface are used to enhance the FIM of the cylinder. Simulations are conducted at Re = 60,000 and Re = 100,000 with the angle of attack, αattack, varies from 0° to 90°. Amplitude response, frequency response, and near-wake structures of the cylinder are discussed in numerical results. The simulation results indicate that both suppression and enhancement of FIM are observed for the cylinder as the angle of attack rises from 0° to 90°. For αattack≥ 55°, the near-wake region becomes quite slender and vortex shedding is suppressed. The FIM of the cylinder is greatly inhibited when αattack ≥55°. In addition, a complex vortex reattachment observed in the near-wake region intensifies the fluid-structure interactions and causes obviously higher amplitude.