# Performance Characteristics of an Orthopter-Type Vertical Axis Wind Turbine in Shear Flows
## 2 Experimental Approach
### Experimental Setup for Shear Flow Cases  
To generate a horizontal shear flow, a perforated panel and a splitter plate were installed at the outlet of the wind tunnel as shown in Figure 3b,c and Figure 4. The perforated panel had a width of 1.0 m, a height of 1.5 m and a thickness of \(2\times 10^{-3}\) m, and was set so that it covered half of the wind tunnel outlet in the horizontal wind direction. Due to the existence of the perforated panel, the pressure upwind of the panel increased and the wind flow rate through the wind-tunnel-outlet area covered by the panel decreased while that through the uncovered wind-tunnel-outlet area increased. When the perforated panel covered the wind-tunnel-outlet area upwind of the retreating side of the rotor, the wind speed of the generated shear flow was higher on the advancing side of the rotor. Hereafter, this type of shear flow is referred to as \"advancing side faster shear flow\" (ASF-SF). On the other hand, when the perforated panel covered the wind-tunnel-outlet area upwind of the advancing side of the rotor, the wind speed of the generated shear flow was higher on the retreating side of the rotor. Hereafter, this type of shear flow is referred to as \"retreating side faster shear flow\" (RSF-SF). The splitter plate was set vertically, parallel to the wind tunnel wall and at the center of the wind tunnel outlet to avoid the horizontal component of the wind velocity in the generated shear flow becoming significant. The splitter plate had a width of 0.88 m, a height of 1.25 m and a thickness of \(4\times 10^{-3}\) m.  
Figure 3: The experimental apparatus and measurement devices; (**a**) in uniform flow, (**b**) in shear flows and (**c**) the porous plate position at the nozzle exit of the wind tunnel in case of shear flows.  
To investigate the effects of the strength of the shear flow on the performance of the O-VAWT, we generated three kinds of shear flows by using three perforated panels shown in Table 1. With regard to a staggered round-hole perforated panel, the shielding ratio \(\Phi\), which is the ratio of the area that shields the airflow to the whole area of the perforated panel, can be computed by:  
\[\Phi\ =\ 1-\frac{\pi\,d^{2}}{2\sqrt{3}\,L^{2}}, \tag{4}\]  
where \(d\) is a diameter of a hole and \(L\) is the distance between the centers of adjacent holes.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name** & \(d\) **[m]** & \(L\) **[m]** & \(\Phi\) **[-]** & **Enlarged View** \\ \hline Perforated panel A & \(3\times 10^{-3}\) & \(4\times 10^{-3}\) & 0.49 & \\ \hline Perforated panel B & \(3\times 10^{-3}\) & \(4.5\times 10^{-3}\) & 0.60 & \\ \hline Perforated panel C & \(3\times 10^{-3}\) & \(5\times 10^{-3}\) & 0.67 & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Perforated panels. Here, \(d\) is the diameter of a hole, \(L\) is the distance between the centers of adjacent holes and \(\Phi\) is the shielding ratio.  
Figure 4: The perforated panel and splitter plate set at the outlet of the wind tunnel.  
Except for the installation of the perforated panels and the splitter plate, the experimental setup for the measurement of the performance of the O-VAWT was the same as the uniform flow case. Prior to the measurement of the performance of the O-VAWT, we measured the horizontal profiles of the generated shear flows at 0.10 m downwind of and at the center height of the wind tunnel outlet by using an x-type hot-wire probe (Kanomax, 0252R-T5).