## 4 Results and Discussion  
### Icing Blade Airfoil Thickness Change  
In order to obtain the iced blade airfoil shape under different icing conditions, the airfoil shapes in a 0.2R section of nine icing blades are taken for comparison. Figure 6 shows the location of the taken airfoil sections; Figure 7 shows the comparison of each section of the airfoil. Figure 5: The 3D scanning site and model building. (**a**) The 3D scanning site; (**b**) Model building. Figure 6: Selected Sections. As can be seen in Figure 7, there is an obvious difference in airfoil shape before and after blade icing. During icing on the windward side and the leeward side, the water droplets will flow lower when they hit the blade at the moment of impact. Thus, windward is a greater effect on the trailing edge, while leeward icing has a greater effect on the leading edge. When the leading edge is iced, the thickness at the trailing edge is basically unchanged, while the thickness at the edge of the airfoil changes very significantly. With the increase in the angle of attack, the position of the ice accumulation from the windward side gradually moved to the leading edge, and the thickness of the ice accumulation at the trailing edge gradually decreased. The ice thickness change on the trailing edge is extremely obvious and the influence on the leading edge is small. In order to accurately describe the effect of icing on the geometrical parameters of the airfoil, the chord length was divided into four equal parts at 0.2R, 0.4R, 0.6R, 0.8R, and 0.95R of the un-iced blade, respectively, with five points distributed at chord length ratios 0, 1/4, 2/4, 3%, and 1, as shown in Figure 8. For the windward side icing, the thickness at five points of the perpendicular intersection is measured with the windward icing contour line. For the leeward side icing, the thickness at five points of the intersection is measured perpendicular to the leeward icing contour line. The trend of thickness changes is shown in Figure 9.  
Figure 7: Comparison of airfoil shapes for different icing conditions for 0.2R cross-section: (**a**) Ising on the windward side of 1.0 kg; (**b**) Ising on the leeward side of 1.0 kg; (**c**) Ising on the leading edge of 0.65 kg and the different angles of attack: (**d**) 0\({}^{\circ}\); (**e**) 15\({}^{\circ}\); (**f**) 30\({}^{\circ}\); (**g**) 45\({}^{\circ}\); (**h**) 60\({}^{\circ}\); (**i**) trailing edge. Figure 8: Airfoil icing measuring point. Figure 9: _Cont._  
From Figure 9a-e, it can be seen that in the case of icing on the windward side, the initial period of icing leads to the most significant increase in the thickness of ice accumulation near the trailing edge. This is due to the more gentle airfoil shape at the trailing edge, and the droplets at monitoring points 3 and 4 at the initial stage slipped off to form ice accumulation, which increased the thickness. As the icing mass increases, the curvature of the trailing edge airfoil increases and the thickness change stabilizes. With the increase in icing mass, the curvature of the leading edge increases, and the thickness change is more uniform. Monitoring points 2, 3, and 4 are located in the middle of the airfoil, the curvature of the airfoil decreases with the increase in icing mass, and it is easier to form ice accumulation. When the ice accumulation reaches the critical value, there is a sudden increase in thickness. From Figure 9e,f, it can be seen that the thickness of ice accumulation near the leading and trailing edges increases most significantly when icing occurs on the leeward side. This is due to the fact that the droplets at monitoring points 2, 3, and 4 slipped toward the ends and the droplets accumulated at the ends, forming ice accumulation. The amount of change in thickness at the leading and trailing edges decreases as the mass of icing increases. When monitoring points 2, 3, and 4 were in the middle of the blade and at the blade root, the thickness change was obvious with the increase in icing mass, and then the thickness change stabilized.