Flutter Based Energy Harvesting Device

Flow around the bluff body has long been discussed before with rigid substrates.16 However, the critical velocity required for the self-sustaining fluttering mechanism is high for rigid substrates. Moreover, most of the studies used lead-based piezo ceramics which are not environmental friendly.16-17, 37-38 However, ZnO is a biocompatible material, and to the best of our knowledge, the studies of ZnO composite for such applications have not been performed yet. We have mounted the device behind a spherical ball (φ=60mm) inside an in-house made wind tunnel. The spherical ball acts as a bluff body which separates the flow thus generating repeating patterns of swirling vortices by the process called vortex shedding. Turek et al. presented a benchmark model for such fluid-solid interaction (FSI).39 However, it mainly focused on the laminar flow past the bluff body, and the research was extended for turbulent flow.40-41 The experimental setup is shown in figure 4a. The inset shows the device mounted upon the bluff body and kept outside the wind tunnel. For the initial characterization, we have taken the voltage response without wind to ascertain that no spurious voltage is produced outside the Faraday cage and the data was plotted as shown in figure 4b.6 Afterward, the wind response in terms of p-p voltage, and the current was calculated at 2.8 m/s. The device was capable of producing peak-peak (p-p) voltage of 0.8 V with 4nA of current. The swiveling frequency was around 4-5 Hz. This phenomenon is usually classified as instability induced excitations (IIE) where instability arises due to the presence of structure in the flow.41-43 The video of the measurement has been shown in the supporting datasheet. The video was also recorded in slow-motion and presented in supporting data. The video clearly shows that during the experiment only a bending mode deformation (1st swiveling mode) taking place without torsional or chaotic mode which are usually characterized as crossover and superposed modes.41 To cross-verify this statement theoretically Perez et al. defined critical flutter/rest velocity is associated with the fluid-solid mass ratio M* is present in equation (2).44
M^*=(L×ρ_f)/〖t×ρ〗_m (2)
where L is the length of the flutter device (65 mm), t is the effective thickness of the device (~50µm in our case (composite and substrate thickness)), ρf is the density of the flutter device (1420 kg/m3), and ρm (1.225 kg/m3) is the density of the medium (air). M* in our case was estimated out to be 1.12 which was in the stable range with the lowest critical velocity among the several reported results by Perez et al.44 Moreover, width to length ratio (H*) is also an essential factor for the efficient flutter phenomenon which was found to be 0.27 in our case and characterized as stable flutter regime. Here, in this experiment, we have performed the piezoelectric characterization for three different velocities as shown in figure 5 (a). As the velocity of air in the wind tunnel is increased, the amplitude of the vibrations increases thus giving a more substantial strain to the device. Larger stress in the piezoelectric devices is directly related to larger electric displacement component thus increasing the piezoelectric output.5 The obtained voltage and current data for different velocities have been shown plotted in figure 5 (b, c). The device was able to harvest approximately 1.6 V and 10 nA p-p voltage and current respectively at 3.8 m/s velocity. Interestingly the swiveling frequency was observed to be around 4-5 Hz confirming the IIE in all the regimes.41
Thus, the demonstrated phenomenon can be used to develop self-powered wind velocity sensors at a meager cost. The increase in current and voltage shows a linear relationship with the increasing air velocity. This is due to the higher induced lift on the device at a higher velocity. To probe further into the device capability, we have mounted the device at a different angle with respect to incoming flow current. Here, in this experiment, we have tested the device for four different angles viz. 0, 30, 60 and 90° as shown in figure 5 (e). The velocity of air used in this experiment was maintained at 2.8 m/s. The measured voltage and current responses of these devices have been shown in figure 5 (f, g). The device was able to harvest energy at a different angle and discern the flow directions.

Published as: Rajagopalan P., Gaurav Khandelwal, I.A. Palani, Vipul Singh, and S.-J. Kim, La-doped ZnO ultra-flexible flutter-Piezoelectric Nanogenerator for Energy Harvesting and Sensing Applications: A Novel Renewable Source of Energy, 10.1039/C9NR02560J, 2019 11, 14032-14041, Nanoscale, IF 6.97;

Part of My PhD work

pubs.rsc.org/en/content/articlelanding/2019/nr/c9nr02560j

My Website: energylabs.webs.com

Author

Ariyani

Como educador, estou profundamente engajado no desenvolvimento dos estudantes em ambiente escolar, adotando métodos pedagógicos que valorizam conexões genuínas e são movidos por inovação e fervor. É minha vocação guiar os alunos na jornada de se tornarem uma geração notável, empregando estratégias de ensino amplamente aclamadas por prestigiadas instituições acadêmicas ao redor do globo - report.dashgoo.com