# Performance Characteristics of an Orthopter-Type Vertical Axis Wind Turbine in Shear Flows
## 4 Results and Discussion
### Flow Characteristics  
Figures 14a, 15a and 16a show the temporal sequence of the horizontal distributions of normalized horizontal velocity vectors, normalized pressure and normalized vorticity, respectively, at the mid-height of the O-VAWT at \(\lambda\) = 0.4 in the case of the uniform flow. At \(\varphi\) = 180\({}^{\circ}\) to 270\({}^{\circ}\), the approaching flow to the blade has a large velocity component perpendicular to the blade, and the pressure on the upwind side of the blade is high. Due to this high pressure, \(C_{TB\_rev}\) is significantly high in the range of \(\varphi\) = 180\({}^{\circ}\) to 270\({}^{\circ}\) in Figure 9. In addition, at \(\varphi\) = 210\({}^{\circ}\) to 270\({}^{\circ}\), due to the strong large vortex formed near the outer edge of the downwind side of the blade, the pressure is low near the  
Figure 13: The variation of blade torque coefficient (\(C_{TB\_rot}\)), its rotor-revolution component (\(C_{TB\_rev}\)) and its blade-rotation component (\(C_{TB\_rot}\)) in the cases of the RSF-SF computed by the CFD simulations; (**a**) for \(\lambda\) = 0.4 and (**b**) for \(\lambda\) = 0.6. Noted that \(C_{TB}\), \(C_{TB\_rev}\) and \(C_{TB\_rot}\) are coefficients of one blade. vortex. This low pressure positively contributes to \(C_{TB\_rev}\) (see Figure 9 at \(\varphi=210^{\circ}\) to \(270^{\circ}\)). By contrast, this low pressure negatively contributes to \(C_{TB\_rot}\) (see Figure 9 at \(\varphi=210^{\circ}\) to \(270^{\circ}\)). At \(\varphi=300^{\circ}\) and \(330^{\circ}\), the approaching flow to the blade has a small velocity component perpendicular to the blade and the pressure on the upwind side of the blade is not high. Therefore, \(C_{TB\_rev}\) is lower as compared to the upwind region of the advancing side of the rotor (see Figure 9 at \(\varphi=180^{\circ}\) to \(270^{\circ}\)). At \(\varphi=0^{\circ}\) to \(120^{\circ}\), the attack angle of the blade is positive (here, the counterclockwise direction is defined as positive) and the flow separates over the outer side of the blade. Therefore, on the upwind edge of the blade and on the inner side of the blade near its upwind edge, the pressure is relatively high. In contrast, on the outer side of the blade near its upwind edge, the pressure is relatively lower. This pressure distribution contributes negatively to \(C_{TB\_rev}\) and positively to \(C_{TB\_rot}\). Figure 14: The temporal sequence of the horizontal distributions of normalized horizontal velocity vectors of the O-VAWT for \(\lambda=0.4\) in the case of; (**a**) the uniform flow, (**b**) the ASF-SF with \(\Gamma=0.51\) and (**c**) the RSF-SF with \(\Gamma=0.51\). Figures 14b and 15b and Figure 16b show the temporal sequence of the horizontal distributions of normalized horizontal velocity vectors, normalized pressure and normalized vorticity, respectively, at the mid-height of the O-VAWT at \(\lambda=0.4\) in the case of the ASF-SF with \(\Gamma=0.51\). At \(\varphi=210^{\circ}\) to \(330^{\circ}\), the approaching flow to the blade has a larger velocity component perpendicular to the blade, and the pressure on the upwind side of the blade is higher as compared to the uniform flow case. Due to this higher pressure, \(C_{TB\_rev}\), is higher than the uniform flow case (see Figure 12 at \(\varphi=210^{\circ}\) to \(330^{\circ}\)). In addition, at \(\varphi=210^{\circ}\) to \(240^{\circ}\), wind speed is significantly increased at the outer edge of the blade and a significantly stronger and larger vortex is formed near the outer edge on the downwind side of the blade. Near the vortex, the pressure is lower as compared to the uniform flow case. This low pressure contributes to higher \(C_{TB\_rev}\) and lower \(C_{TB\_rot}\) as compared to the uniform flow case (see Figure 12 at \(\varphi=210^{\circ}\) to \(240^{\circ}\)). At \(\varphi=120^{\circ}\) and \(150^{\circ}\), the pressure on the outer side of the blade is lower due to the lower speed approaching flow to the blade.