Presently, researchers globally are suited and booted with a single aim of developing alternative renewable energy technologies. This conquest has been highly motivated by the increasing carbon footprint traceable everywhere in present economic activities coupled by the inevitable depletion of non-renewable energy resources. Such endeavors have led to the proposition of various technologies; of concern here being the development of flow-induced vibration (FIV) energy harvesters. In literature, there are two different categories related to energy harvesting through FIV, namely: Vortex excitation (VE) like vortex-induced vibrations (VIV) and fluid-elastic vibrations like galloping and flutter. Previously, due to the large strains and geometric deformations, these types of induced vibrations have been in the past classified as destructive phenomena. However, common and accessible flow-induced vibration could be considered as a way to extract energy. As such, various types of flow-induced vibration have been investigated as an external source for energy generation.
Reports have it that vortex-induced vibrations energy harvesting is the most promising, nonetheless, it suffers from some critical drawbacks thereby restricting efficient energy harvesting from vortex-induced vibrations to some extent. Specifically, interaction between the gap flow force and the drag force has triggered considerable research attention.
To this end, Yokohama National University researchers Hamid Arionfard and Professor Yoshiki Nishi studied the performance of a double cylinder flow-induced vibration energy converter. They goal was to take advantage of drag force and gap flow to enhance the vibration. Their work is currently published in the research journal, Renewable Energy.
Generally, cylinders free to rotate around a pivot and located in different configurations including both cylinders on the downstream, both on the upstream, a cylinder on each side and one cylinder on the pivot. The same setup was adopted for this study where each configuration was represented by the gap ratio between the two cylinders (G=gap/cylinder diameter) and center of gravity ratio (CG = gravity center/cylinder diameter). By combining the most popular approaches, i.e. a drag assisted vibration (for rotational oscillations) and two circular cylinders in proximity range (the most basic method of generating GSIV), the two researchers were able to investigate a range of vibration mechanisms like vortex-induced vibrations, WIV and galloping as well as GSIV and drag-assisted vortex-induced vibrations.
The authors recorded that the highest displacement amplitude was observed for CG = -0:25; G = 0:4 where the drag force assist the vibration because CG < 0. In addition, the VEfN was seen to be the second most efficient mechanism. Moreover, the third most efficient mechanism was the drag-assisted configurations (CG < 0).
In summary, a novel device for generating clean and renewable energy from fluid-induced vibration has been introduced by Arionfard and Nishi. The approach presented employed two mechanically coupled cylinders used as harvesters, with the two being free to rotate around a pivot point. Remarkably, the setup made it possible to activate and use different types vibration mechanisms other than vortex induced vibration and wake-induced vibration that have been the main focus of the previous researches.
Hamid Arionfard, Yoshiki Nishi. Experimental investigation on the performance of a double-cylinder flow-induced vibration (FIV) energy converter. Renewable Energy, volume 134 (2019) page 267-275.Go To Renewable Energy