“…The galloping vibration in Case 1 has been observed in previous studies and we note significant similarities between galloping in Case 1 and flow-induced pitching and heaving of an airfoil reported in earlier studies (Tamimi et al. 2022). However, the galloping vibrations in Case 3 are significantly different and have not been observed earlier. In Case 2, the modal amplitude ratio () can be effectively utilized to attain an undamped FIV suppression due to the self-limiting characteristics of the tandem cylinder FIV amplitudes.In Case 3, out-of-phase vibrating tandem cylinders of Case 3 indicate a higher energy harvesting potential with a single energy harvesting unit, as compared with the uncoupled tandem cylinders in Case 1 with two energy harvesting units.…”
Section: Discussionsupporting
confidence: 88%
“…Tamimi et al. (2022) reported a similar galloping response of a pitching-heaving airfoil. Figure 21.Schematic description of the mechanism of galloping for ( a ) Case 1, ( b ) Case 2 and ( c ) Case 3.…”
Section: Discussionmentioning
confidence: 79%
“…Tamimi et al. (2022) also reported suppression of the galloping vibrations for a pure heaving airfoil, i.e. if the pitching motion of the airfoil is arrested.…”
We numerically study the transverse flow-induced vibration (FIV) of elastically coupled tandem cylinders at Reynolds number
$100$
, using an in-house immersed boundary method-based solver in two-dimensional coordinates. While several previous studies considered tandem cylinders coupled through flow between them, a hitherto unexplored elastic coupling with fluid flow between them significantly influences FIV. We consider a wide range of gap ratio, reduced velocity, an equal mass ratio of both cylinders and zero damping. A systematic comparison between the classic elastically mounted tandem cylinders and elastically coupled cylinders is presented. The latter configuration exhibits two vibration modes, in-phase and out-of-phase, with corresponding natural frequencies approaching the Strouhal frequency of the system. We quantify variation of the following output variables with reduced velocity and gap ratios: cylinders’ displacement; fluid forces; amplitude spectral density of displacement and force signals; phase characteristics; energy harvesting potential; and discuss the wake characteristics using flow separation, pressure distribution, gap flow quantification, and dynamic mode decomposition characterization. The FIV response is classified into several regimes: initial desynchronization with and without gap vortices; final desynchronization; mixed mode; initial branch; lock-in; upper and lower branch; wake-induced vibration; galloping. We draw upon similarities of computed FIV characteristics with those of an isolated cylinder, in which the lower branch exhibits larger a amplitude than the upper branch. The elastically coupled cylinders show a galloping response similar to an isolated D-section cylinder. By invoking the elastic coupling, we demonstrate FIV suppression and augmentation for in-phase and out-of-phase systems. Our calculations show larger energy harvesting potential at reduced cost for elastically coupled cylinders.
“…The galloping vibration in Case 1 has been observed in previous studies and we note significant similarities between galloping in Case 1 and flow-induced pitching and heaving of an airfoil reported in earlier studies (Tamimi et al. 2022). However, the galloping vibrations in Case 3 are significantly different and have not been observed earlier. In Case 2, the modal amplitude ratio () can be effectively utilized to attain an undamped FIV suppression due to the self-limiting characteristics of the tandem cylinder FIV amplitudes.In Case 3, out-of-phase vibrating tandem cylinders of Case 3 indicate a higher energy harvesting potential with a single energy harvesting unit, as compared with the uncoupled tandem cylinders in Case 1 with two energy harvesting units.…”
Section: Discussionsupporting
confidence: 88%
“…Tamimi et al. (2022) reported a similar galloping response of a pitching-heaving airfoil. Figure 21.Schematic description of the mechanism of galloping for ( a ) Case 1, ( b ) Case 2 and ( c ) Case 3.…”
Section: Discussionmentioning
confidence: 79%
“…Tamimi et al. (2022) also reported suppression of the galloping vibrations for a pure heaving airfoil, i.e. if the pitching motion of the airfoil is arrested.…”
We numerically study the transverse flow-induced vibration (FIV) of elastically coupled tandem cylinders at Reynolds number
$100$
, using an in-house immersed boundary method-based solver in two-dimensional coordinates. While several previous studies considered tandem cylinders coupled through flow between them, a hitherto unexplored elastic coupling with fluid flow between them significantly influences FIV. We consider a wide range of gap ratio, reduced velocity, an equal mass ratio of both cylinders and zero damping. A systematic comparison between the classic elastically mounted tandem cylinders and elastically coupled cylinders is presented. The latter configuration exhibits two vibration modes, in-phase and out-of-phase, with corresponding natural frequencies approaching the Strouhal frequency of the system. We quantify variation of the following output variables with reduced velocity and gap ratios: cylinders’ displacement; fluid forces; amplitude spectral density of displacement and force signals; phase characteristics; energy harvesting potential; and discuss the wake characteristics using flow separation, pressure distribution, gap flow quantification, and dynamic mode decomposition characterization. The FIV response is classified into several regimes: initial desynchronization with and without gap vortices; final desynchronization; mixed mode; initial branch; lock-in; upper and lower branch; wake-induced vibration; galloping. We draw upon similarities of computed FIV characteristics with those of an isolated cylinder, in which the lower branch exhibits larger a amplitude than the upper branch. The elastically coupled cylinders show a galloping response similar to an isolated D-section cylinder. By invoking the elastic coupling, we demonstrate FIV suppression and augmentation for in-phase and out-of-phase systems. Our calculations show larger energy harvesting potential at reduced cost for elastically coupled cylinders.
We develop a high-fidelity multi-physics model and, by using it, study the energy conversion process of a piezohydroelastic flag. Instead of a regular flag with a clamped upstream leading edge, we use an inverted flag so as to make the best of fluid elastic instability for energy harvesting. Moreover, different from many previous studies where a resistor–capacitor (RC) circuit is usually used, we adopt a resistor–inductor–capacitor (RLC) circuit for electricity generation. The influences of several key parameters associated with fluid, structure and electric dynamics are studied. Significantly different response modes are identified, among which the symmetric- and asymmetric-flutter modes are most suitable for sustainable energy harvesting, both emerging with moderate bending stiffness. If only deploying the RC circuit, increasing the resistance makes the flag more stable. By adding an inductor to turn the RC circuit into an RLC one, we observe the occurrence of ‘lock-in’ between the flag frequency and the circuit frequency as first reported on a regular flag by Xia et al. (Phys. Rev. Appl., vol. 3, 2015, 014009). This phenomenon can significantly enhance the energy output, but it only happens when the circuit resistance is sufficiently large. From a derivation based on dynamic mode decomposition analysis, we further identify an optimal condition for maximizing the energy output, which can serve as a guideline to determine whether deploying an inductor can boost the performance, and, if yes, the required inductance. The findings from this study can better guide the design of flow-induced-vibration-based piezoelectric energy harvesters for microelectronic devices.
“…TENGs are a field that effectively converts mechanical energy into electric power, − and its working modes and material options are various. − Many researchers have demonstrated the excellent harvesting energy ability of TENGs in the water flow environment. − TENGs with different structural designs are used to harvest water flow energy, all of which require a certain flow velocity. − Thereby, it is concerning that the energy harvesting of a TENG can be limited under low-flow velocity. Flow-induced vibration exists in abundant kinetic energy, which is a self-excitation vibration at low-flow velocity. − TENG-based energy harvesting technology can convert hydrokinetic energy into electric power . The cross-sectional differences of the bluff body brings diverse vortex effects, which then have an impact on the performance output of the TENG.…”
A general problem is that the energy harvesting of lowvelocity rivers closely related to human life is difficult. Herein, a softbionic-fin structure triboelectric−electromagnetic generator (SF-TEG) with swing-rotation mechanism is proposed. It consists of a bionic fintype soft body and a power generation part including the triboelectric nanogenerator (TENG) and electromagnetic generator (EMG). Specifically, the soft body driven by the vortex effect acquires swing, which brings the TENG to obtain oscillation and then drives the EMG to realize water flow energy harvesting. The TENG and EMG attain the output voltages of 143 to 203 V and 4.6 to 7.7 V, respectively, under flow velocities from 0.34 to 0.96 m/s. The output voltages of the TENG and EMG retain about 98% and 100%, respectively, after 4 h of continuous work. Additionally, the SF-TEG can harvest water flow energy from open channels to power sensors to provide temperature, humidity, and light intensity for greenhouses.
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