Energy harvesting efficiency from fluid flow by vortex-induced vibrations:reduced-order modeling
[Objective]Vortex-induced vibration(VIV)is a well-known fluid-structure interaction phenomenon that holds promising potential for harnessing energy from fluid flows.The pursuit of optimizing energy conversion efficiency from VIV has garnered significant interest.However,considerable challenges,such as the costs of experiments and computational fluid dynamics(CFD)simulations,pose significant hurdles in conducting comprehensive global optimization studies on efficiency.[Methods]In response to these challenges,this study employs a reduced-order model(ROM)based on a wake oscillator.The ROM is used to compute and optimize the energy harvesting efficiency from the VIV of a circular cylinder.The rapid computational capabilities of the ROM allow the creation of high-resolution efficiency maps across various mass ratios and Reynolds numbers.These maps encompass a broad spectrum of incoming velocities and damping ratios.They not only provide valuable insights into achieving maximum efficiency but also detailed information on the optimal damping ratio and velocity.To validate the predictions of the ROM,comparisons are drawn against experiments and CFD simulations.For cases with high Reynolds numbers(high-Re),the ROM is validated using published experimental data.Conversely,for low-Re cases where experimental data is sparse,a computational fluid-structure interaction solver,named CFD-FSI,is utilized.This tool relies on direct simulations to verify the ROM results.Despite some differences observed between the ROM,experimental outcomes,and CFD data,this study demonstrates that the maximum efficiency and its occurrence conditions predicted by the ROM are acceptable.With its cost-effectiveness,the ROM emerges as a valuable tool for investigating optimal energy harvesting efficiency and providing insights into related engineering aspects.[Results]Overall,the main findings of this study can be summarized as follows:1)This study contributes high-resolution global optimization maps for energy harvesting efficiency from VIV,focusing on the optimization parameters of reduced velocities and damping ratios.Additionally,it offers a cost-effective approach and solution through the use of ROM.This method seeks to achieve a high efficiency from VIV across a large number of tested cases.2)The maximum efficiency point is found to be influenced by the incoming velocity and the product of the mass ratio and damping ratio.This implies that if fluid flow conditions,such as the Reynolds number,remain constant,the global maximum efficiency remains consistent across different VIV energy converters despite having various structural configurations.Additionally,for different VIV energy converters,the product of the mass and the optimal damping ratio,where the global maximum efficiency occurs,tends to be similar.3)Efficiency at a high Reynolds number is shown to surpass that at Re=150 in laminar flows.This is primarily attributed to differences in lift coefficients and Strouhal numbers between high-and low-Reynolds flows.From the perspective of the ROM,a high lift coefficient might contribute to a higher converted efficiency.[Conclusions]Considering the definition of the mass ratio,the study suggests that the energy harvesting efficiency of a lighter system is more robust than that of a system with a high mass ratio.This indicates potential advantages for ocean VIV energy converters over wind VIV energy converters.Furthermore,the present work provides an effective tool to predict,analyze and optimize the energy harvesting efficiency from VIV,which would be helpful for related engineering design and future studies on this topic.
fluid-structure interactionvortex-induced vibration(VIV)energy harvestingreduced-order model
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