## 3 Results and Discussions
### Analysis of Velocity, Pressure and Torque Fields
Figure 12 shows the graphs of the change in the torque coefficient Cm depending on the rotor rotation angle \(\theta\) with a diameter D = 3.75 m and different chord lengths. At c = 0.2 m (Figure 12a), the torque remains positive over the entire interval, but the oscillations are small and weakly expressed, which may indicate insufficient aerodynamic activity. At c = 0.4 m (Figure 12b), the curve has a clear sinusoidal shape with a high amplitude and positive torque values, which indicates stable and efficient operation. At c = 0.6 m (Figure 12c), significant negative values of Cm appear, alternating with positive ones, which indicates unstable rotor operation and possible brak  
increase in the chord length to 0.8 m (Figure 12d), the torque coefficient almost completely goes into the negative region, reaching values below -1, which indicates inefficient and even braking operation of the wind turbine. Thus, at D = 3.75 m, the best characteristics are observed at c = 0.4 m, while values c \(\geq\) 0.6 m led to a significant decrease in efficiency. Figure 13 shows the graphs of the change in the torque coefficient Cm depending on the rotor rotation angle \(\theta\) for a rotor diameter of D = 4 m and different chord lengths. For c = 0.2 m (Figure 13a), the torque remains stable and positive, but has a low amplitude, which indicates weak aerodynamic efficiency. For c = 0.4 m (Figure 13b), the graph shape becomes clear and sinusoidal, with pronounced peaks and positive Cm values, which indicates the most balanced and efficient operation of the rotor. As the chord increases to 0.6 m (Figure 13c), the torque goes into the negative region, which indicates braking and instability phases. For c = 0.8 m (Figure 13d), deep negative values down to \(-\)1.5 are observed, which indicates a critical decrease in efficiency and the predominance of the braking torque. Thus, at D = 4 m, the best rotor performance characteristics are observed at a chord length of c = 0.4 m, while values from 0.6 m and above lead to deterioration of aerodynamic properties. The analysis of the change in the torque coefficient Cm depending on the rotor rotation angle showed a clear dependence of the aerodynamic efficiency of the wind turbine on the combination of the rotor diameter and the blade chord length. At small chord lengths (c = 0.2 m), the torque values remain positive, but low and weakly expressed, indicating a limited ability of the blades to generate useful aerodynamic force. With an increase in the chord to 0.4 m, most combinations demonstrate a stable, smooth, and predominantly positive behavior of the torque with a pronounced periodicity. This indicates the most balanced operation of the turbine, especially with diameters from 1.5 to 3.75 m. At c = 0.6 m, the torque coefficient increases in amplitude, but in many cases negative sections appear, especially at large diameters, indicating flow instability and possible braking phases. With a further increase in the chord to 0.8 m, the moment becomes predominantly negative, reaching extremely low values, which indicates a decrease in the efficiency of the rotor due to excessive aerodynamic resistance. Thus, based on the results obtained, it can be concluded that the optimal ratio of geometric parameters for stable and efficient operation of the [PERSON] rotor is achieved with a chord length of about 0.4 m in a wide range of rotor diameters.