Experimental Investigation of Energy Harvesting in the Wake of Circular Cylinder using Cantilever Pivoted Piezoelectric (Eel)

Abstract

Set of experiments are designed and executed in a water tunnel to study the impacts of pivoted mounting mechanism on piezoelectric flag and to observe improvement in the parameters associated with energy harvesting. For this purpose, we performed experiments using circular cylinder and two identical cylinders in tandem arrangement which are placed in a uniform fluid flow. Modes depicting parameters of energy harvesting are extracted by motion capturing of tail evolution of the flexible flapping flag over the period of 120 seconds by postprocessing in MATLAB. Different flapping modes, such as those with weak and ideal coupling to the wake flow, were demonstrated by experimental data. We noticed the two mechanisms that help push the flag in either direction. The first process involves the impingement of induced flow caused by passing vortices on one side of the flag, while the second involves the presence of the low-pressure core regions of the vortices on the opposite sides of the flag which relates to the finding of Akaydin H. et al. (2010). The sequence of these two effects combined with the free pivoted head of the flag generated maximum values for dominant flapping frequency and normalized amplitude (A/L). And also experiments showed that the streamwise gap (Gx) and flow speed (U m/s) have a significant impact on the amplitude and flapping frequency. The results indicate that with the use of pivot mounting, the flapping amplitude (A/L) is increase by a margin of 51.18% while dominant flapping frequency increases for about 22.79% as compared to U. Latif et al. (2021) results for stationary head mounted flag behind circular cylinder. For further improvement of parameters, we placed an identical cylinder at upstream of current cylinder. This tandem arrangement proved to have adverse effects on the vortex shedding and hence less efficient results obtained due to less net energy & poor coupling of flag with the wake flow. Particle Image Velocimetry (PIV) of cylinder wake also endorses the results of J.Wu et al. as wake dynamics and vortex shedding under for gd/D=1.0, 1.5 and 2.0, are in good agreement with the flag behavior. The present study contributes effectively to harvesting energy from impinging vortices by tuning the streamwise gap, flow velocity, and mounting mechanism for the flexible flag (EEL).