*4.1. Operational Cases and Boundary Conditions*

The turbine is designed to operate in the wind speed range varying from 6 to 12 m/s. However, the numerical tests were also performed for velocities above this range, in extreme cases, for the structural strength evaluation. Four particular wind cases were investigated: the maximum thrust operation at normal operation, overload condition (twice the normal wind speed), and extreme loads (*V* = 42 m/s) for two rotor modes: working and stopped. Extreme working load corresponds to the point just before stopping the turbine, while static corresponds to when the turbine has stopped. Overload conditions correspond to the case between the upper limit of operational condition (max thrust) and extreme loads. Each of these cases corresponds to different flow parameters given in Table 3.


**Extreme static load** 42 - 0 0

The blade of the wind turbine is subjected to two types of loads: pressure from flowing fluid and centrifugal forces. Therefore, in the case of the analyzed blade, following loads and boundaries are assumed (see Figure 7): fixed support at the beginning of the blade – in the place where the blade is in contact with the hub (A); the rotational velocity of the blade enabling to calculate deformations due to centrifugal forces (B); pressure fields imported from fluid flow simulation (C, see exemplary imported pressure in Figure 8).

**Figure 7.** Applied loads and boundary conditions.

**Figure 8.** Map of imported pressure on the pressure and suction sides of the blade (results in [Pa]).
