This study proposes a cross-coupled dual-beam structure for energy harvesting from vortexinduced vibrations (VIV) induced by wind flows in different directions. A series of wind tunnel tests are conducted to investigate the performance of the proposed energy harvester subjected to the wind load with various speeds and directions. The upper and bottom piezoelectric beams can generate a maximum power output of 6.77 μW and 56.64 μW, respectively. The dominant operation frequencies in different directions are different which indicates a potential broadband capability. A parametric study is performed to reveal the effect of the dimension of the bluff body on the performance of the proposed energy harvester.
This study evaluated the performance of twin adjacent galloping-based piezoelectric wind energy harvesters based on mutual interference. The relative position between the twin harvesters is crucial to their energy generation efficiency. A series of wind tunnel tests were conducted to test energy generation of the two harvesters in tandem or staggered arrangements. The optimal relative position, a streamwise center to center spacing of 1.2B (B is the width of the harvester's square prism) and a transverse center to center spacing of 1.0B, was identified. The total output power of the two harvesters placed in the optimal relative position is up to 2.2 times that of two isolated harvesters. The output power is also much larger than that of the harvesters in tandem arrangements that have been widely tested in previous studies. Therefore, it is recommended to position two adjacent harvesters in optimal relative position(s) to deliver an optimal power output.
Schools of fish can provide individuals with hydrodynamic advantages, thereby improving the swimming efficiency. Fish schools in nature are mostly spatial configurations, not just limited to the horizontal plane. Through three-dimensional numerical simulations, this paper discusses the hydrodynamic characteristics and flow field structure of fish schools in various vertical patterns. The results show that a school of fish arranged vertically can improve the thrust and swimming efficiency of individuals as well as those arranged horizontally. There are two ways to significantly enhance hydrodynamic advantages. One is to maximize the channeling effect in multiple planes. In a vertical circular pattern, the fish school forms multiple coupled channels, which hinder the free expansion of flow in both vertical and horizontal planes, thereby obtaining higher energy-saving benefits. The other is the combined exploitation of the channeling effect and wake energy, which is illustrated in the vertical rectangular pattern. The following fish can use the channeling effect to increase the thrust due to the presence of parallel companion. Meanwhile, the high speed region of the following fish can merge with the jet flows of the preceding fish, thereby capturing the wake energy and further improving swimming efficiency.
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