The effects of the span length of the prism, and the gap between the splitter plate and the prism on the performance of the vibrational power generator by the flow induced vibration and the magnetostrictive material were investigated with the w ind tunnel experiment. The splitter plate was added to improve the performance of a vibrational power generator with a cantilevered rectangular prism and a side ratio D H of 0.4 (where D is the depth of the prism in the flow direction and H is the height o f the prism). The span length L of the rectangular prism was 200 mm and 300 mm. The high speed galloping vibration occurs in cases with a small gap. The vibration onset flow velocity and power generation are affected by the span length of the prism. As t he long span rectangular prism (i.e., L = 300mm) has a low characteristic frequency and starts to vibrate at a low wind velocity, this prism has a wide range of wind velocity for power generation as compared with the short span prism (i.e., L = 200 mm).

A vibration energy harvester was developed using a magnetostrictive material as a power generator and a prism as a wind receiver to harvest energy from low-speed wind by exploiting flow-induced vibration. The present cantilevered vibration power generator has originality for the structure which consists of a U-shaped unimorph beam of Galfenol (iron-gallium alloy). Wind tunnel experiments were conducted for prisms having circular, rectangular, filleted triangular, and V-shaped cross-sections. We focused on transverse vortex-induced vibration for a circular cylinder and low-speed galloping vibration for a rectangular prism with a depth-to-height ratio of 0.2, a filleted triangular prism, and a V-shaped prism. The effect of the width of prisms having a span length of L 200 mm on the transverse vibration characteristics and the power extracted from the vibration generator was investigated. The maximum power generated by cylindrical, rectangular, filleted triangular, and V-shaped prisms with heights of 50, 50, 60, and 50 mm was 1.28, 3.5, 7.83, and 5.02 mW, respectively. These maximum power levels are enough to run a wireless sensor. Moreover, the angle of the V-shaped prism having a width of 50 mm was varied (i.e., B= 60°, 90°, 120°, and 150°) and tested in wind tunnel experiments. The V-shaped prism with B= 120° was best from several viewpoints, including low excitation wind speed, safe operation at high wind speed, efficient operation in environmental conditions, and sustainability.

Small wind turbines are efficient for solving power supply problems in remote off-grid regions. A crossflow wind turbine is a drag-based small vertical axis wind turbine, which is suitable for small-scale power generation in the built environment because of its low aerodynamic noise. However, the power performance of a crossflow wind turbine is generally lower than that of a Savonius wind turbine. Aiming at improving the performance of a crossflow wind turbine, this study develops a wind concentrator by adding two parallel plates with flanges, which is based on the “wind lens” concept, to an arc-shaped windshield, which is based on an existing concept of a flow deflection device for a crossflow wind turbine. The effects of adding two parallel plates with flanges to the windshield (i.e., the effects of the wind concentrator) on the performance of the crossflow wind turbine are quantified with wind tunnel experiments and analyzed based on the flow field characteristics obtained by computational fluid dynamics simulations. The experimental results show that the wind concentrator enhances the maximum power coefficient of the crossflow wind turbine by 108% from 0.12 (without wind concentrator/windshield) to 0.25 (with the wind concentrator), whereas the arc-shaped windshield improves it by 48% from 0.12 to 0.17 (with the windshield). The numerical simulations reveal that the main cause for the power performance enhancement is a downward deflection of the approaching flow to the upper part of the rotor because of a significant increase in the pressure level on the upwind side of the upper flange and an overall decrease in the pressure level in the wake of the wind concentrator. In conclusion, adding two parallel plates with flanges to an arc-shaped windshield is effective for significantly enhancing the power performance of a crossflow wind turbine.