Exploring the potential benefits of using metasurface for galloping energy harvesting

Abstract

Inspired by the successful applications of metasurfaces in many other fields, this paper aims to explore the potential application of metasurfaces in designing aerodynamic systems. Bluff bodies are proposed to be wrapped in metasurfaces for improving galloping energy harvesting. Three different metasurfaces with convex cylinder, tri-prim, and wedge ornaments are designed. A general aeroelastic model for a galloping energy harvester is developed. The aerodynamic force is represented by a polynomial function with its coefficients being determined from three-dimensional CFD simulations. Subsequently, physical prototypes of the proposed galloping piezoelectric energy harvesters are fabricated, and experimental tests are conducted. The theoretical model is validated by the experimental results. The analytical method and three-dimensional CFD simulation are combined to predict the dynamic responses of the metasurface-wrapped GPEHs. Besides, the results show that the metasurface can significantly change the aerodynamic characteristics of the bluff body, and it is learned that a bluff body wrapped in convex cylinder metasurface could bring benefits for promoting galloping energy harvesting performance. Further experimental studies are conducted to reveal the effects of convex ornament parameters on the galloping energy harvesting performance. It is found that using the metasurface distributed with convex cylinder ornaments of diameter 6 mm and height 9 mm leads to the largest vibration displacement and largest voltage output. Compared to the typical GPEH, the maximum vibration displacement and maximum output voltage of the proposed galloping piezoelectric energy harvester can be increased by 26.81% and 26.14%, respectively. The vortex shedding processes around the wind flow fields near the bluff bodies wrapped in metasurfaces are simulated. The underlying aerodynamic mechanism of the influence of the metasurfaces is unveiled. Finally, based on the validated theoretical model, a parametric study is carried out to investigate the effects of the load resistance and electromechanical coupling strength on the galloping energy harvesting performance. It is concluded that increasing the coupling strength to a certain level and tuning the load resistance to the optimal value could further improve the power output. However, when the electromechanical coupling strength increases to a certain extent, the power output will reach the saturation state, and the coupling strength is extremely large. Therefore, a piezoelectric element with a moderate coupling coefficient is recommended for practical applications from the perspective of economic benefit.