## 3 Results and Discussion
Point (C) in Figure 8a refers to the rotor rotation angle of 262\({}^{\circ}\). In this angular position of the rotor, blade 1 is located in the aerodynamic shadow behind blade 3, as shown in Figure 16a. As a result, an increase in wind pressure is observed only on one lower blade lobe, as presented in Figure 16b. In contrast, the upper lobe is not significantly pressurized. The aerodynamic shadow effect, which occurs only in the CFD simulation, is the reason for the discrepancy between the numerical and analytical results. Figure 17a,b show the CFD-based drag and lift forces of three rotor blades. The results are for the second to fifth rotations. It can be observed that the variation in the drag and lift forces is the same for all the blades. The drag and lift forces obtained from CFD simulation were used to calculate the driving torque. Figure 18 shows the variation in the driving torque for three rotor blades for the analytical and CFD-based approaches. The components of the driving torque were calculated considering the fourth revolution of the rotor. Table 8 summarizes the average driving torque and the average power. For CFD-based results, the fourth rotation of the rotor was considered. It can be noticed that the error between analytical and CFD approaches referring to the average torque and power values was about 1%. Figure 14: Results of CFD simulation for \(\alpha=200^{\circ}\): (**a**) velocity distribution; (**b**) pressure distribution. Figure 15: Velocity pathlines around blade 1 for \(\alpha=200^{\circ}\). Figure 16: Results of CFD simulation for \(\alpha=262^{\circ}\): (a) velocity distribution; (b) pressure distribution. Figure 17: (a) Drag force; (b) lift force for blade 1. Figure 18: Driving torque on blades for a single rotor rotation. The main limitations of vertical-axis wind turbines are self-starting difficulties at low wind speed and the low starting torque, particularly when considering lift-based Darrieus-type rotors with NACA profiles [41]. Self-starting disabilities are especially observed for common H-rotor turbines. External mechanical or electrical devices are often used to overcome these kinds of design inadequacies [23]. An additional objective of this study was to demonstrate the main advantage of the carousel wind rotor design, which has a significantly higher starting torque in comparison with the H-type Darrieus rotor. [PERSON] et al. [22] analyzed the starting conditions of H-type Darrieus rotors with three NACA0015 airfoils that were adopted for the comparison. The following parameters and assumptions were accepted by the authors: rotor radius of 1.25 m, chord length of 0.4 m, blade span of 3 m, wind speed of 10 m/s, and tip speed ratio \(\lambda=0.2\). The reported torque coefficient for the starting conditions was \(C_{m}=0.023\). The analytical model developed in this study was used to determine the torque coefficient for the self-starting conditions of the carousel wind rotor with dual-coherent blades. The geometrical scale factor of 7.8 was used to adjust the analytical model to the corresponding rotor dimensions. The obtained torque coefficient was \(C_{m}=0.31\), which was more than 13 times higher than for the considered H-type Darrieus rotor.