# Design and Optimization of Vertical Axis Wind Turbines Using QBlade
## 5 Results and Discussions  
In order to obtain the model of the rotor and the design for different VAWT types, the NACA4418 for the blade was selected as shown in Figure 3. Each blade divided to a finite number of blade sections. For each blade section, the design parameters of circumferential position, vertical position, radial position, length of the chord, and type of airfoil was introduced. All airfoil sections of straight blades have the same radius and circumferential position. In order to enhance the design of the blade of the vertical axis wind turbine and decrease the time consumption to find the results, scaling and optimization functionalities are used as illustrated in Figure 4. These parameters are height scaling, height shifting, chord scaling, radius scaling, and twist scaling to speed up the rotor modification. The analyses were performed on the blade of the turbine within range (1 to 10 of tip speed ratio \(\lambda\)). In this analysis, a constant velocity of 7 m/s was used, while the rotation of the rotor was varied concerning \(\lambda\). As a result, the power coefficient and torque values vs. various tip speed ratios can be seen in Figures 5 and 6, respectively. At low \(\lambda\), the rotor does not spin and therefore, under such conditions, it cannot obtain power from the wind. There  
Figure 2: Flowchart of the developed approach to analyze and optimize the vertical axial wind turbine. would be an acceptable value at the maximum power which is derived between \(\lambda=1\) and \(\lambda=10\). This would be the situation within the average speed of the rotor which is \(2/3\) of the wind speed in compliance with the Betz law. At the high value of \(\lambda\), the rotor runs faster, and the chance to extract energy from the wind will decrease because the mass transports (wind) through the rotor will be reduced. The optimum values of the design parameters were selected as inputs in the algorithm used in the software (DMS algorithm). During the computation process, it was assumed that the velocity of a free stream would be unified and it was used for the normalized dimensions of the rotor (height and radius). Figure 4: The details of the blade optimization process. Figure 3: Design of 3 blades of VAWT. Furthermore, the graph type of DMS simulation is available to determine the multi-parameters as shown in Figure 7. Power is not only dependent on the tip speed ratio but also on the rotational speed and pitch angle. For the range that started from 200 to 500 rpm with an increment of 100 of tip speed ratio TSR, four groups of results were obtained. It can be noticed that when power increased, the TSR increased, too. The power versus the wind speed was presented for 3 blades of VAWT using the simulation operation as shown in Figure 8.  
A rotor blade should be presented in the runtime database and parameters (rotor blade, cut-in and out wind speed, turbine offset, fixed and variable losses) of the wind that is to be specified to define the wind turbine. Comparisons between 3, 4, and 5 blades of VAWT rotor simulation were made as shown in Figure 9. It was noticed that the coefficient of performance \(Cp\) increased when the number of blades increased, too. The maximum values of \(Cp\) were observed at TSR = 5 for the 3 blades (VAWT), and at TSR = 4.5 for the 4 blades (VAWT), while the maximum \(Cp\) recorded for the 5 blades of VAWT was at TSR = 4. Additionally, it can be noticed that when using 5 blades, the values of \(Cp\) (after maximum value) are decreased until TSR = 6 and then increased. While for the other cases (3 and 4 blades), the values of \(Cp\) decreased gradually. Figure 5: Coefficient of performance (\(Cp\)) vs. tip speed ratio (TSR) for 3 blades of VAWT. Figure 6: Torque vs. tip speed ratio (TSR) for 3 blades of VAWT. Figure 10 shows the change of lift coefficient with drag coefficient for 3 blades of VAWT using XFOIL direct analysis in QBlade. Figure 4.0 Power (\(W\)) vs. wind speed (m/s) for 3 blades of VAWT.