## 4 Numerical Results
### Cavitation Shape with Cavitator Angle of Attack  
Factors that determine the maximum diameter and length of the cavitation are Fn at ambient speed and Cq and \(\sigma_{\rm C}\) at the injection rate. In addition, there are angles of attack of the cavitator that can have a very large impact in real environments. In this study, we studied how the shape of cavitation changes when the cavitator has an angle of attack. Figure 12 shows the cavitation shape change according to the angle of attack of the cavitator in the injection cavitation computational analysis with the injection characteristic of Cq = 0.15. When the angle of attack (AoA) is 0\({}^{\circ}\), the cavitation asymmetry due to the rise of the cavitation tail due to the gravity and buoyancy effect occurs as shown in Figure 6. If the angle of attack is 10 degrees, the cavitation generated from the cavitator is generated below the body, thereby canceling the asymmetry of the cavitation trailing edge caused by buoyancy. When the angle of attack is 15\({}^{\circ}\), the cavitation shape becomes more prominent, and it can be seen that the cavitation covers more area under the body. Figure 13 shows the height (h) from the body surface to the maximum cavitation diameter with the cavitator angle. The maximum cavitation diameter means the largest point formed on the upper and lower, respectively. As the cavitator angle increases, the asymmetry of the cavity is formed with a larger distance from the lower surface to the cavitation maximum diameter. In the case of the upper surface, when the angle is 15 degrees, the distance to the maximum diameter of the cavitation is greatly reduced. Figure 14 shows the length of the shape of the cavity according to the angle of attack. The solid line indicates the distance to the point where the maximum cavitation occurs. As the cavitator angle increases, it can be seen that it increases slightly without significant difference. The dotted line represents the cavitation debtatching length. When there was no angle of attack, the upper length was longer. However, as the angle of attack increased, the upper length and lower length became the same and eventually reversed. Being able to predict the length of the cavitation according to the angle of attack is important information in maintaining the super cavitation. Asymmetric formation of cavitation with changes in cavitator angle is related to body shape characteristics. In the case of the analyses of Figures 12-14, the diameter of the cavitator is similar to that of the body, so the cavitation generated from the cavitator propagates well backward. As shown in Figure 15, in real scale the diameter of the body is larger than the diameter of the cavitator. In this geometry, the change in cavitation size caused by the angle of attack of the cavitator can have a significant effect on the body's motility. Figure 15 shows the result of changing the angle of attack to \(-10^{\circ}\), \(+10^{\circ}\), and \(+20^{\circ}\) for the case of the super cavitation formed around the high-speed underwater vehicle. At 0\({}^{\circ}\), there is no wetted surface where water and body come in contact with anything other than the front of the cavitator. In addition, it can be confirmed that the cavitation asymmetry does not occur due to the buoyancy effect as shown in Figure 12 even though the angle of cavitation is 0\({}^{\circ}\) due to the high-speed condition. In this case, when the angle of attack has a value of 10\({}^{\circ}\) in the upward direction, the generation of the cavitation to the lower surface is limited. Therefore, the receiving surface, where the cavitation is destroyed and the water and the body come into contact, occurs at 14d\({}_{\rm c}\) from the front. The destroyed cavitation will recover and cover the body again, but one can see that the receiving surface occurs once again at 48 d\({}_{\rm c}\).