The flow-induced vibration (FIV) of multiple cylinders is a common phenomenon in industry and nature. The FIV and energy harvesting of three circular cylinders in tandem are numerically studied by 2D-URANS simulations in Reynolds number range of 30,000 < Re < 105,000. Simulation results match well with experiments in the tested cases. Four branches of FIV are clearly captured in the amplitude and frequency ratio curves of the three cylinders with roughness, including initial branch of vortex-induced vibration (VIV), VIV upper branch, transition from VIV to galloping, and galloping. It is shown that the vortices from downstream cylinder are strongly disrupted and modified by vortices of upstream cylinder. The third cylinder is almost suppressed in VIV initial branch. The 2P vortex pattern is observed for the first cylinder in the VIV upper branch. For Re = 90,000 in the transition regime, the vortex patterns of the first and second cylinders are 2P + 4S and 2P + 2S, respectively. In the galloping branch, the shear layer motion is in synchronization with the motion of the cylinder, and the maximum amplitude of 2.8D is reached by the first cylinder. The total converted power of the three cylinders increases with U^*_water both in the simulation and experiment. For the three cylinders, the maximum power reaches up to 85.26 W with the increase of Reynolds number. The energy conversion efficiency is stable and higher than 35% in the starting region of VIV upper branch, and the maximum value of 40.41% is obtained when Re = 40,000.

The influence of fin-shaped rod (FSR) with different installation positions on wind-induced vibration and energy harvesting of a cylinder-based aeroelastic energy harvester are studied by experiments and simulations. Two FSRs are installed symmetrically on the surface of a circular cylinder, and the coverage angle of each FSR is 20°. The installation position of FSRs on the cylinder is represented by the placement angle, θ , which varies in the range of ±160°. And the tested wind speed range is 0–6.8 m s ⁻¹ . The results show that FSRs change the position of the separation point of the boundary shear layers, further affect the formation and shedding of vortices. Then the force on the cylinder changes, which causes the energy harvester to produce different vibration responses and energy outputs. When 0° < θ < 70°, back-to-back vortex-induced vibration (VIV) and galloping can be observed for FSR-cylinder, and the output power increases with the increase of wind speed, the maximum output voltage and power reach 18.1 V and 1.645 mW. For 70° ⩽ θ < 120°, the vibration of FSR-cylinder is suppressed, which is not conducive for energy harvesting. When 120° < θ ⩽ 160°, the vibration of FSR-cylinder firstly experiences VIV and then galloping occurs after reaching the critical wind speed.

The effect of cross thermal buoyancy on the characteristic of flow-induced vibration and mixed convection of three circular cylinders is numerically studied. Two-dimensional simulations were conducted for a Reynolds number (Re) of 100 and five Richardson numbers (Ri) of 0-1.00. The range of reduced velocity is 3{less than or equal to}U^*{less than or equal to}15. The three circular cylinders C1, C2, and C3 are arranged in an equilateral triangle with C1 in upstream. The results show that the maximum amplitude of the C1 increases by up to 21% with considering cross thermal buoyancy in comparison to the case of Ri=0. The galloping-like response is observed on the C1 at Ri=1.00. The lift coefficient of three circular cylinders increases with the increase of Ri at U^*{greater than or equal to}6. When U^* exceeds a critical value, the vibrations of the C2 and C3 are in-phase, the "2S" pattern is observed in the near-wake of three circular cylinders. The near-wake becomes wider and the vortex shedding frequency increases at U^*=6, Ri=0.25 and 0.50. The higher the reduced velocity, the more significant the effect of cross thermal buoyancy in enhancing heat transfer. The maximum space time-averaged Nusselt number increases by 10.42% in comparison to the case of fixed cylinders.

The effect of tandem spacing on the flow-induced motions (FIM) of two circular cylinders with passive turbulence control is investigated using two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model. Results are compared to experiments in the range of Reynolds number of 30,000 < Re < 100,000. The center-to-center spacing between the two cylinders is varied from 2 to 6 diameters. Simulation results predict well all the ranges of FIM including vortex-induced vibrations (VIV) and galloping and match well with experimental measurements. For the upstream cylinder, the amplitude and frequency responses are not considerably influenced by the downstream cylinder when the spacing is greater than 2D. For the downstream cylinder, a rising amplitude trend in the VIV upper-branch can be observed in all the cases as is typical of flows in the TrSL3 flow regime (transition in shear layer 3; 2 × 10⁴< Re < 3 × 10⁵). The galloping branch merges with the VIV upper-branch for spacing greater than three-dimensional (3D). Vortex structures show significant variation in different flow regimes in accordance with experimental observations. High-resolution postprocessing shows that the interaction between the wakes of cylinders results in various types of FIM.

Wind-induced vibration (WIV) and power extraction performances of a circular cylinder with symmetrically installed fin-shaped rods (FSR) were experimentally and numerically investigated under different coverages. The FSR coverage which is expressed as an angle ( α ) is measured from the upstream edge to the downstream edge of the rod. The effect of FSR installation angle ( θ ) which is the angle from the stagnation point of cylinder to the upstream edge of the rod was also considered in this work. The FSR cylinder is exposed in uniform wind and allowed to vibrate in cross-flow direction. The output electric power is realized by piezoelectric patch. It is found that, for most cases, the output power of FSR cylinder increases monotonously with the rise of α for a given wind velocity ( U ). In addition, the tendency of output voltage varies with the wind velocity is highly similar to that of output power. The maximum values of output voltage and power are 19.70 V and 1.90 mW can be obtained when α = 20° ( θ = 60°). The WIV responses of FSR cylinder show that the amplitudes of FSR cylinder increase with the rise of α for low installation angle ( θ = 0°, 30°) and the maximum amplitudes exceed 2 D ( D : diameter of circular cylinder) can be observed for α = 40°/50° ( θ = 30°) and α = 20° ( θ = 60°). The reduced frequency of cylinder for θ = 0° and 30° does not sensitive to the coverage ( α ). It is worth noting that multiple frequencies can be captured for high coverage. Due to the boundary layer separating point moves in downstream direction with the increase of U and α , the vortex pattern switches from 2S to 2P.