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).
