## 3 Results and Discussions
### Analysis of Velocity, Pressure and Torque Fields
Figure 8: _Cont._  
Figure 8: Pressure distribution contour for all combinations considered: (**a**) D = 1.5 m; (**b**) D = 2.25 m; (**c**) D = 3 m; (**d**) D = 3.75 m; (**e**) D = 4 m.  
Figure 9: Change in average torque coefficient Cm depending on rotation angle \(\theta\) for D = 1.5 m. (**a**) D = 1.5 m; c = 0.2 m, (**b**) D = 1.5 m; c = 0.4 m, (**c**) D = 1.5 m; c = 0.6 m, (**d**) D = 1.5 m; c = 0.8 m.  
Figure 11: Change in average torque coefficient Cm depending on rotation angle \(\theta\) for D = 3 m. (a) D = 3 m; c = 0.2 m, (b) D = 3 m; c = 0.4 m, (c) D = 3 m; c = 0.6 m, (d) D = 3 m; c = 0.8 m.  
Figure 9 shows the change in the torque coefficient Cm depending on the rotor rotation angle \(\theta\) for a diameter D = 1.5 m and different blade chord lengths. In Figure 9a, at c = 0.2 m, sharp torque fluctuations with peaks and dips are observed, which indicates unstable turbine operation and a significant influence of turbulent effects. In Figure 9b, at c = 0.4 m, the Cm curve takes an almost sinusoidal shape with a high amplitude and stable periodicity, which indicates a more efficient and balanced rotor operation. In Figure 9c, at c = 0.6 m, it demonstrates an even smoother and more stable torque distribution while maintaining a high average value, which may indicate approaching the optimal operating mode. In Figure 9d, at c = 0.8 m, the average torque level decreases, and the oscillations become less symmetrical, which indicates a drop in efficiency due to increased resistance. Thus, the most favorable conditions for torque generation are achieved with a chord length of 0.4-0.6 m.  
Figure 10 shows the graphs of the change in the torque coefficient Cm depending on the rotor rotation angle \(\theta\) for a rotor diameter D = 2.25 m and different chord lengths. In Figure 10a, at c = 0.2 m, the curve has a low amplitude, and Cm remains positive over the entire range, but the values are low, which indicates a weak torque. In Figure 10b, at c = 0.4 m, deep oscillations with high positive and negative peaks are observed, which indicates a strong influence of unstable aerodynamic effects and uneven load distribution. In Figure 10c, at c = 0.6 m, it shows a stabilized sinusoidal shape with high positive torque values and minimal negative surges, which can be interpreted as an efficient and balanced rotor operating mode. In Figure 10d, at c = 0.8 m, a moderate decrease in amplitude is observed, although the torque remains predominantly positive. Thus, with a diameter D = 2.25 m, the most effective in terms of value and stability of the moment is a chord  
Figure 12: Change in average torque coefficient Cm depending on rotation angle \(\theta\) for D = 3.75 m. (a) D = 3.75 m; c = 0.2 m, (b) D = 3.75 m; c = 0.4 m, (e) D = 3.75 m; c = 0.6 m, (d) D = 3.75 m; c = 0.8 m.  
length of 0.6 m, while at 0.4 m, undesirable instability with a possible reverse moment is observed. Figure 11 shows the change in the torque coefficient Cm depending on the rotor rotation angle \(\theta\) for a diameter D = 3 m and different blade chord lengths. For c = 0.2 m (Figure 11a), the curve has a clear sinusoidal shape with fairly high amplitudes, but there are sections where the torque becomes negative, which may indicate instability in certain phases of rotation. For c = 0.4 m (Figure 11b), the graph remains positive over the entire range, and the oscillations are moderate and smooth, which indicates stable and efficient operation of the rotor. On the graph with c = 0.6 m (Figure 11c), the Cm values become extremely high, but also fluctuate strongly, including significant negative sections, which indicates unstable operation and sudden overloads. For c = 0.8 m (Figure 11d), the curve again takes a regular shape, remaining in the positive region, but the amplitude decreases. In general, the most balanced result in terms of stability and efficiency is observed at c = 0.4 m, while at c = 0.6 m overloads and instability occur.