The curves corresponding to the single blade are shown in Figure 10b, respectively for the Straight and Helical configurations. Sin. 2001, 19, 427–433. [Google Scholar]Howell, R.; Qin, N.; Edwards, J.; Durrani, N. Wind tunnel and numerical study of a small vertical axis wind turbine. Figure 10a instead shows the three-blade curve trend. It can be seen that the curve of the Helical blade is smoother than that of the Straight blade. Furthermore, it has been shown, by comparing three-dimensional with two-dimensional results, that the generation of the tip vortices greatly reduces the aerodynamic performance. This phenomenon is more evident in the Straight blade geometry (Figure 14), where vortices accumulate mainly at blade tips. On the contrary, in the Helical blade geometry, vortices are evenly distributed along the blade trailing edges. Four distinct wind turbine configuration are taken into account, namely the Straight blades VAWT and three Helical blades VAWT with different twist angles.
Static and dynamic results are then reported for different values of rotational speed. Among the renewable energy sources, onshore wind power is one of the most attractive because of its low cost of maintenance of installed systems. The sliding mesh model  is used to model the turbine blade rotation. A multiple reference frame solution  is used to compute a flow field as an initial condition for the transient sliding mesh calculation. Renew. Energy. 2010, 35, 412–422. [Google Scholar]Zhang, L.; Liang, Y.; Liu, X.; Jiao, Q.; Guo, J. Aerodynamic performance prediction of straight-bladed vertical axis wind turbine based on CFD. Adv. Sci. 1998, 33, 759–846. [Google Scholar]Qian, W.; Fu, S.; Cai, J. Numerical study of airfoil dynamic stall.
Subsequently, three-dimensional static analyses of four different configurations, ψ = 0°, 30°, 60°, 90°, have been performed. Carrigan et al. , fixing the tip speed ratio (TSR) of the wind turbine, developed an iterative design system to maximize the torque for different airfoil cross-sections and solidities in two-dimensional CFD simulations. Static results for Blade 2 and Blade 3 differ from Blade 1 data for a phase shift of +120° and −120°, respectively. Strickland  extends Templin’s approach into a multiple single streamtube model by considering a number of adjacent smaller streamtube, applying the conservation of momentum and blade element theory to each streamtube.