A synergistic vortex generator, composed of upstream double plates and a downstream cylinder with small spacing, is investigated through numerical simulations to enhance wake effects and, subsequently, the power output of a piezoelectric energy harvesting system in a flowing water environment.

The simulations illustrate the synergistic mechanisms, demonstrating that adjusting the angle of the double plates allows the synergistic vortex generator to produce distinct wake patterns compared to the configurations with double plates or a cylinder alone, significantly impacting the dynamic behavior and power output of the harvester. Notably, when the double plate angles are set at -15 • and 30 • , the asymmetric double-plate wake type generates high-frequency, large-amplitude vibrations in the flexible piezoelectric flag, resulting in stable power output, which cannot be achieved by classical cylinder-based and double-plate-based harvesters. In particular, at the angle of -15 • , the synergistic harvester exhibits a 190% increase in amplitude, a 127% increase in vibration frequency, a 1000% increase in power output, and a 280% improvement in energy harvesting efficiency compared to cylinder-based harvesters. At larger double-plate angles (-90 • to -45 • and 60 • to 90 • ), the reduced blockage from the plates weakens the vortex strength they generate, leaving the flexible piezoelectric flag predominantly influenced by the vortices shed from the cylinder. However, the flag's vibrations remain significantly enhanced compared to cylinder-based systems due to the merging of wakes from both the double plates and the cylinder.

Overall, the larger the angle of the plates, the weaker the synergistic enhancement effect. Additionally, different angles lead to varying wake center velocity profiles, with the centerline velocity of the double-plate wake type generally lower than that of the cylinder wake type. Thus, future optimizations of energy harvester arrays could benefit from adjusting the plate angles to maximize collective power output.