Abstract
This numerical study investigates the flow-induced vibration responses and energy harvesting characteristics of a low-mass square oscillator. We first test three typical incidence angles of α = 0°, 22.5°, and 45° with reduced velocities Ur ranging from 3.8 to 26. The most interesting phenomenon is that large-amplitude vibrations can be generated at high reduced velocities, regardless of the angle α. We show that this is because of the following mechanisms: (i) For α = 0°, galloping occurs, resulting in high-amplitude and low-frequency vibrations; (ii) for α = 45°, the cylinder undergoes vortex-induced vibrations (VIVs) without the high-amplitude galloping instability. The unsteady vortex shedding effects are enhanced by a very low mass ratio, leading to “VIV forever” in the tested range of Ur with high-level amplitudes; and (iii) for α = 22.5°, the oscillations in the high-Ur range include both VIV and galloping components. Thus, the large amplitude is caused by the galloping instability and enhanced vortex-shedding effects. Due to the existence of large-amplitude vibrations, the low-mass square cylinder demonstrates the potential and necessary robustness for energy harvesting applications. Overall, α = 45° is the most suitable arrangement for the conversion of power. To further improve the efficiency, we test a 45° cylinder under damping ratios ζ ranging from 0.01 to 0.7. The results indicate that the energy harvesting characteristics are sensitive to the damping ratio when ζ < 0.3. Of all the tested cases, ζ = 0.7 provides the highest average efficiency.
Highlights
The exhaustion of environmental resources is in sharp contrast to the increasing energy demands of our society
The results indicate that the energy harvesting characteristics are sensitive to the damping ratio when ζ < 0.3
For the circular cylinder under scitation.org/journal/adv flow, a low mass ratio may lead to the vortex-induced vibrations (VIVs) forever phenomenon, that is, the amplitude exists at the high-reduced-velocity range even though the oscillation frequency is desynchronized from the natural frequency f s
Summary
The exhaustion of environmental resources is in sharp contrast to the increasing energy demands of our society. For a low-mass square cylinder, the QST model fails to predict the efficiency because of the enhanced unsteady vortex shedding effects.[37,43,44] energy harvesting by a low-mass cylinder is of interest due to the strong interactions that may occur between the VIVs and galloping. Because of the possible galloping instability, the low-mass-ratio behavior of a square cylinder has not yet been clarified ( for high Reynolds numbers) and its mechanism cannot be inferred from the circular cylinder cases For this reason, it is necessary to investigate whether a low-mass square cylinder can exhibit VIV forever and, more importantly, to analyze whether the lowmass effects can be effectively applied for energy harvesting. To address the above aspects, we use CFD simulations to investigate the FIV responses and energy harvesting characteristics of a low-mass square cylinder with different incidence angles and damping ratios at high Reynolds numbers.
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