Numerical study into the impact of fixed upstream cylinder diameter ratios on vibration of leeward tandem cylinders

Multiple-cylinder fluid flows present challenges due to the strong interference between wakes, shear layers, and Kármán vortex streets, resulting in high-amplitude vibration responses. Despite these challenges, recent research has explored the potential for extracting hydrokinetic energy from such phenomena. In the present study, high-fidelity simulations are performed for flow-induced vibrations (FIV) of large spacing tandem cylinders, located leeward of a fixed cylinder with a small spacing ratio. The objective is to investigate the effect of diameter ratios of the upstream fixed cylinder on the energy conversion of its leeward tandem cylinders. Vibration responses of the midstream and downstream cylinders are identified by analyzing their amplitudes, frequencies and force coefficients, as well as vorticity contours. Results show that the presence of a large fixed upstream cylinder generates large vortices capable of synchronizing the vibrations of leeward cylinders, resulting in regular, larger amplitudes, and higher power harnessing efficiency compared to a fixed upstream cylinder with smaller diameters. Overall, this study contributes to a better understanding of fluid–structure interactions and their potential for energy conversion in multiple-cylinder systems. •Fluid-induced vibrations of multiple cylinders are numerical studies with a focus on their potential for energy harvesting.•Impact of varying diameter ratios of a fixed upstream cylinder on its leeward cylinders with unequal spacing ratios is investigated.•Vibration responses, force coefficients, vorticity contours, and synchronization of the cylinders are analyzed.•Results demonstrate the potential of utilizing configurations with varying upstream cylinder diameters to improve power generation.