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The growing demand for sustainable energy solutions for autonomous IoT sensors and
remote monitoring devices has driven interest in piezoelectric energy harvesting from
ambient fluid flows. This study investigates wake-induced vibrations from PVDF
piezoelectric flags positioned behind dimpled circular cylinders compared to smooth
baseline configurations. Comprehensive water tunnel experiments tested a 25 mm
diameter cylinder at flow velocities of 0.15-0.30 m/s (Reynolds numbers 3500-11500).
Nine dimpled configurations were evaluated, featuring three dimple diameters (9, 11, and
13mm) arranged in 3, 4, and 5 columns. Flag was positioned at streamwise gaps of 1D3D downstream. Data acquisition included real-time measurements of voltage, high
velocity analysis of video, and Particle Image Velocimetry (PIV) for wake
characterization. Smooth circular cylinders significantly outperformed all dimpled
configurations and achieved peak power output of 15.2 μW at 2D spacing and 0.30 m/s,
maintaining optimal wake width. Performance degraded systematically among dimpled
configurations: 3-column arrangements outperformed 4-column designs, which exceeded
5-column configurations, while smaller dimples consistently outperformed larger ones.
The best dimpled cylinder (3-column, 9mm dimples) achieved only 91.45% of smooth
cylinder performance, while the worst configuration (5-column, 13mm dimples)
delivered merely 59.41% of baseline output. PIV analysis revealed dimple-induced
boundary layer energization promotes premature flow reattachment, reducing wake width
and vortex formation length, thus diminishing downstream energy availability. Optimal
energy harvesting occurs at 1.5D-2.5D spacing, peaking at 2D regardless of
configuration. These findings provide critical design guidance for marine sensors,
structural health monitoring, and autonomous underwater vehicles, demonstrating that
smooth cylinders optimize VIV energy harvesting. This research advances understanding
of fluid-structure interactions in energy harvesting and provides practical guidelines for
sustainable micro-power generation systems.