Performance enhancement of wind energy harvester utilizing wake flow induced by double upstream flat-plates

Small-scale wind energy harvesting system is being considered to provide green long-term electric power to unattended sensor network nodes which are widely used in urban and natural environments. This paper proposes that placing a double-plate structure upstream of the bluff body in the wind energy harvesting system can significantly improve the output performance. At a certain wind speed, two wake flow zones with low-pressure are formed behind two upstream side-by-side plates, which induced the bluff body at the downstream intermediate position to deviate to both sides. Even at a low wind speed, the vibration of bluff body can still occur because the pressure fluctuation of the wake zone disturb the static equilibrium. Placing the double plates upstream of a wind energy harvester with a cylinder can change the vibration response from VIV (vortex-induced vibration) to galloping. Moreover, when the ratios of the horizontal and vertical distances to the windward width of the cylinder are 1 and 0.5, respectively, the cut-in wind speed is as low as 1.5 m/s. For the galloping-based wind energy harvester with a square prism, after the double plates are placed upstream, the cut-in wind speed decreases from 3.5 m/s to 1 m/s and the output voltage increases from 1 V to 12 V at 1.5 m/s. The increase of voltage caused by the addition of double plates to the upstream of six different bluff bodies indicates the good adaptability of this structure. The higher voltage output capability by this method at low wind speed significantly expands the application scope of wind energy harvesters.