Numerical predictions of vibration responses and flow energy conversion efficiency of side-by-side cylinders at moderate Reynolds number

Vortex-induced vibration (VIV) of two circular cylinders in a side-by-side (SBS) configuration was modelled using three-dimensional numerical simulation at Reynolds number Re = 1,000. The VIV parameter values used for the study were mass ratio, m* = 10.0, damping ratio, zeta = 0.01, and a range of reduced velocities, U-R* = 2.0 to 10.0. Various VIV responses were investigated, such as amplitude, frequency, and response correlation for gap ratios 1.0 <= g* <= 3.0. Moreover, the efficiency of flow energy conversion was determined to assess the potential of this configuration for VIVACE (Vortex-Induced Vibration Aquatic Clean Energy). For comparison, the VIV responses and efficiency of the single-cylinder case were also presented with identical variables. It was found that the optimal gap ratio between the SBS cylinders was in the interval of 1.0 <= g* <= 1.2. A significant increase in efficiency occurred in the initial excitation region between 4.0 <= U-R* <= 5.0. Above this range, the efficiency was less than that of a single cylinder. In the case of SBS cylinders, the soft lock-in appeared to start early. The anti-phase correlation led to a significant increase in the vibration response as well as efficiency. The increase in maximum efficiency was more than twofold.