## 6 Applications
### Large Scale DeepWind 5 MW  
The DeepWind 5 MW turbine has been simulated with the 3D BEM code considering the rotor axis tilt of 15\({}^{\circ}\), as representative of FOWT actual operation. DeepWind 5 MW concept has been developed in the framework of a European project aimed to optimize aerodynamic and structural components in a coupled approach for floating applications [57,58]. The optimised DeepWind shape led to a new concept which modified the classical Troposkein shape in order to minimize the mechanical stresses (Table 7 and Figure 14). Despite previous research studies focused on operational NACA0018, NACA0025 and DU12W264 blade shapes, herein the comparison is carried out with NACA0021 and DU06W200 profiles. For multi-MW VAWTs a control logic is required to exploit optimal TSRs, therefore a variable rotational speed is imposed. [PERSON] et al. [59] proposed several operating schedules, among which constant rated speed (5.95 rpm) was selected: before reaching the wind speed of 8 m/s (in Table 7 referred as 'Wind speed @ rated rpm'), the rotational speed varies linearly with the wind velocity. In Table 7 the relevant geometric characteristics of the rotor are listed according to [60]. A wind shear coefficient of \(\alpha_{w}=0.14\) was assigned to model the atmospheric boundary layer, which represents a typical value for offshore applications. The wind speed distribution \(V_{\infty}\) is referred to \(z_{EQ}=65.55\) m above sea level, where the DeepWind 5 MW exhibits the largest radius of 60.49 m, while blade attachment with the tower is placed at 15 m above sea level. The analysis aims at establishing proven design choice at the preliminary stage and also at estimating the effects of main parameters on VAWT aerodynamic performance. In Figure 15, results of sensitivity analyses on airfoil shape, rotor tilt and wind shear are shown. Rotor tilt evidently affects turbine efficiency below the rated wind speed of 15 m/s with a reduction of power accordingly. Wind shear, with reference to baseline condition, exceeds rated power because of higher wind speeds over the most part of the turbine height, provided that reference wind velocity is assumed to be at the equatorial plane. The overall superposition of the effects of rotor tilt and wind shear yields to a \(C_{P}\) reduction of almost 15% points from the baseline case (no wind shear, no rotor tilt). First, the predominant effect of the rotor axis tilt on the peak power coefficient, Figure 14(a), and peak power, Figure 14(d), is observed: the free stream reduction due to the inclination of the turbine tower is 10%. The introduction of a freestream wind velocity profile with \(\alpha_{w}=0.14\) originates a sensitive increase in turbine performance only because the rotor portion above the equatorial plane experiences a higher approaching velocity since the  
Figure 13: Sensitivity analysis to airfoil shapes: NACA0021 and DU06W200 of small H-shaped and Troposkein Savona rotors. reference freestream speed is considered at the equatorial section. It is therefore noted that the effects of tilt and wind shear do not linearly combine and the overall performance is lower with respect to the one with only rotor axis tilt. Such result represents an important conclusion which might benefit from a systematic comparison with high-fidelity CFD simulations, as both effects need a complex treatment and involve a high level of resolution, which demand proper assessment. As a matter of fact, it should be noted that the Reynolds number is in the order of \(10^{7}\), where no experimental data are available and polar construction is only based on XFOIL calculations. Correlated to that, DU06W200 profile overcomes NACA0021 because of enhanced aerodynamic performance of the former at high Reynolds number. The outcomes at high wind speeds shrink lowering the TSR, and the differences among the different configurations above rated speed become less relevant.