Mr. Zhicheng Kai Profile

Zhicheng Kai

at Rose-Hulman

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Proceedings Article | 20 April 2022 Presentation + Paper

Quantifying aerodynamic coupling for side-by-side piezoelectric harvesters in fractal-grid-generated turbulent flow

Zhicheng Kai, Amir Danesh-Yazdi

Proceedings Volume 12043, 120430O (2022) https://doi.org/10.1117/12.2610953

KEYWORDS: Turbulence, Energy harvesting, Energy efficiency

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The power harvested by non-tunable fluidic energy harvesters such as piezoelectric cantilever beams in turbulent flow is significantly smaller than that of tunable harvesters whose natural frequency can be tuned to match the dominant flow frequency. Incorporating a tandem of beams allows the power output per beam to be improved in such cases due to the additional contribution of aerodynamic coupling. In this paper, we explore the effect of beam configuration and length, gap-to-width ratio, mean flow velocity and distance from the grid on the aerodynamic coupling-to-input ratio and electromechanical efficiency for two side-by-side beams subjected to turbulence generated by a fractal I, fractal square and a fractal cross grid patterns. We introduced the aerodynamic coupling-to-input ratio in an earlier paper as a means to measure the influence of the aerodynamic coupling on the energy conversion process. Our results show that the electromechanical efficiency and coupling-to-input ratio are larger for a shorter, stiffer beam tandem than longer, more flexible beams irrespective of the fractal grid used to generate the turbulence. Furthermore, we have found the aerodynamic coupling force to be a much larger percentage of the force applied to the beams for the fractal turbulence grid cases, especially the fractal I pattern, compared to a conventional rectangular grid.

Proceedings Article | 22 March 2021 Presentation + Paper

Evaluation of aerodynamic coupling in side-by-side piezoelectric beams in quiescent and grid-generated turbulent flow

Zhicheng Kai, Amir Danesh-Yazdi

Proceedings Volume 11588, 1158817 (2021) https://doi.org/10.1117/12.2582699

KEYWORDS: Stochastic processes, Turbulence, Aerodynamics

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Non-resonant harvesters such as piezoelectric cantilever beams that extract energy from turbulence-induced vibration are often nonviable alternatives to their resonant counterparts. In the quest for enhanced viability, such fluidic harvesters can be positioned side-by-side and incorporate the aerodynamic coupling between them to improve power output. In this paper, we derive the power budget and electromechanical efficiency of two side-by- side beams subjected to an impact load in quiescent flow and grid-generated turbulence. We also introduce the aerodynamic coupling-to-input ratio and aerodynamic coupling effectiveness as ways to measure the influence of the aerodynamic coupling on the energy conversion process. The theoretical derivations are used to evaluate the aforementioned terms for two cases: (i) one beam subjected to a ringdown test in quiescent flow and (ii) both beams exposed to grid-generated turbulence. The influence of gap-to-width ratio, mean flow velocity and distance from the grid on each term has also been considered in this analysis. Our results show that while the aerodynamic coupling-to-input ratio exponentially decays with respect to the gap-to-width ratio for the ringdown test case, it remains relatively constant and non-zero with increasing gap-to-width ratio for the turbulence cases considered.

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