*4.3. Stresses and Deformations—Discussion*

The structural assessment of the wind turbine has been performed on structural mesh no. III as the mesh with the smallest number of elements and fulfilling all convergence criteria. For all considered cases, tip deflection, maximal equivalent stresses and deformation twist have been calculated using one-way coupling FSI. The data are presented in Table 6. Moreover, tip deflections and maximal equivalent stresses appearing in the structure as the function of wind speed and TSR are presented in Table 6, respectively.

**Table 6.** Tip deflection, maximal equivalent stresses, and deformation twist for all considered cases (mesh III).


From the point of view of this study, a very significant parameter is the deformation twist of the blade. The value of this parameter strongly affects the efficiency of the turbine, as it results in operation of the airfoil in adverse, out-of-design conditions. If Δβ is too high, a stall may occur and provoke efficiency drop. In this case, however, the study proves that the angular deformation of the blade should not have a significant influence on the rotor efficiency. Numerical tests had shown that considered structure is not twisting more than 0.05◦, which is a very good result, indicating that the consecutive blade sections are well in their operation regions. The total deflection of the blade is not playing a significant role because the total area of the blade is almost constant. Summing up, according to these results, it can be stated that deformations of the blade will not affect its operation.

The last parameters to be analyzed are equivalent stresses (Von Mises). In the case of the blades, the highest stresses are appearing in the middle of the length of the blade and near connection with the hub. The flexural strength of Polyamide PA66 MO is equal to 109 MPa. This value is not exceeded for any of the considered cases, meaning that the turbine is structurally safe.
