Piezoelectric energy harvesting

Rectangular bluff bodies of uniform area cross-section and attached to two piezoelectric cantilevers are subjected to a uniform flow. Flow induced vortices cause the piezoelectric cantilevers to vibrate (VIV) in a suction-type wind tunnel that we study to understand influence of different flow and structural parameters. The cantilevered-rectangular bluff body had cross-section length and height ratios B-by-D (B/D) in the range 0.25 < B/D < 0.95. B values between the different B/D ratios are 6.35 mm, 12.7 mm, and 19.05 mm to avoid 5% blockage of the wind tunnel. The thinner (6.35mm) bluff bodies are then susceptible to deformation at higher wind speeds. Between the different combinations of B/D and incident wind speeds, voltage generated ranged from 0.36 V (noise) to 20 V. Images of the vibrating bluff bodies were captured using high speed video and compared with the voltage levels generated as a function of incident wind speed (1.8-4 m/s). The ratio of natural frequency to vibration frequency proved to be an indicator of operating efficiency. The operating limit for each bluff body of a given B/D ratio was established in terms of non-dimensional parameters such as Reynolds number (Re)(1000-5300), Strouhal number (St) estimates from the literature, dimensionless mass ratio (1.2-2.6).