## 3 Results and Discussions
### Performance of New Omni-Directional Wind-Funnel Design
The boundary of the bluff splitter body model was fixed. The surfaces of the PVEH plate model were set as fluid-structure interfaces, which allow the data exchange of fluid and structure models. FSI simulation results were used to simulate the electrical performance in terms of open-circuit voltage and short-circuit optimal power output under the electromechanical-coupling condition. The CFD module setup is shown in Figure 9 for input wind speeds of 5 m/s, 7.4 m/s 10 m/s, 15 m/s, 20 m/s, 25 m/s, and 30 m/s at the inlet, when the outlet is set with the reference pressure of 1 atm. In this study, the SSG Reynolds stress turbulence model was applied. The total time steps set for the simulation were 600 or 0.3 s, with the time step at 5 \(\times\) 10\({}^{-4}\) s used. For each time step, a maximum of 5 iterations were used for the CFD solver and a maximum of 10 iterations were used for the FSI coupling solution, respectively. Figure 8: Resonant frequency and corresponding mode shape of PVEH plate under cantilevered boundary condition. As shown in Figure 10, a bell-curve trend of vibration amplitude against wind speed is observed, in which the amplitude increases when the wind speed increases, until it reaches the peak maximum amplitude at 20 m/s wind speed, before it starts the downward trend. It could be related to the structural resonance phenomenon, in which a higher vibration amplitude is produced when the vortex frequency is close to or coincides with the resonant frequency of the model. Meanwhile, Figure 11 shows that the vortex frequency increases proportionally with wind-speed magnitude. When the vortex frequency lies near or coincides with the PVEH plate's resonant frequency, it causes structural resonance lock-in and leads to a high vortex-induced vibration amplitude of the PVEH plate. A vortex frequency of 80.1 Hz created at 20 m/s coincides with the model's resonant frequency of 80 Hz, and, thus, resonance happens and produces the highest VIV amplitude of 1.167 mm and a voltage output of 20.99 V. At wind speeds below 20 m/s, it is noted that the VIV amplitudes produced are low, as the vortex frequencies created are not close to the model's resonant frequency. It is also noted that at higher wind speeds, i.e., 25 m/s and 30 m/s, which create the vortex frequencies of 93.5 Hz and 103.5 Hz, respectively, are also far away from the resonant frequency of the model, and, thus, the resonant mode contributes less to the overall vibration. Due to this, the PVEH plate is vibrating at a relatively lower VIV amplitude, i.e., 0.438 mm and 0.264 mm, as well as an open circuit voltage output, i.e., 7.99 V and 4.85 V, respectively, at these two wind speeds, despite having a higher fluctuating lift force. Figure 10: Vibration amplitude and voltage output of the PVEH plate under different wind speeds. Figure 9: The 3D fluid domain simulation setup of coupled model of bluff splitter body and PVEH plate. Figure 11 shows that when wind speed increases, the fluctuating lift force acting on the surface of the PVEH plate also increases. It is noted that higher flow speed could induce lower pressure surrounding the region of vortex and produce higher force, which acts on the opposite of the plate's surface. The vortex is unstable by nature and, when it achieves steady condition, it usually produces a periodical fluctuating lift force with a certain frequency. It is noted that a larger wind speed creates a higher vortex frequency because the alternating lift force is created at higher rate and acts on the PVEH plate. Figure 11 shows that higher wind speeds of 25 m/s and 30 m/s produce a larger lift force, acting on the surface of the PVEH plate. However, the vibration amplitude produced is lower compared with the vibration amplitude produced at an input wind speed of 20 m/s, because there is a mismatch between the vortex frequency created and the resonant frequency of the model. In summary, vortex-induced vibration amplitude is affected more by the vortex frequency than the fluctuating lift force.