## 4 Discussion of Simulation Results
### Self-Propulsion Simulation
#### 4.1.2 Evaluation of Propeller Performance in Self-Propulsion Point  
Because the propeller was installed in the stern of the underwater glider, the actual flow field under the self-propulsion condition is different from that under the open water condition. Without considering the non-uniformity of the flow field, the average inflow  
Figure 19: Self-propulsion point calculation of series Kappel propeller with diamond wing underwater glider, speed of 6 kn (**a**), speed of 5 kn (**b**), speed of 4 kn (**c**), speed of 3 kn (**d**). Figure 20: Relationship between self-propulsion point speed and series Kappel propeller models. velocity in front of the propeller disk under the self-propulsion condition is different from that of the hybrid-driven underwater glider, so it is necessary to obtain the actual inflow velocity of the propeller. In the self-propulsion simulation example, the velocity distribution in a circular section with an outer diameter of 0.25 m, an inner diameter of 0.05 m, and an area of 0.04712 m\({}^{2}\) at 0.16D upstream of the propeller disk is intercepted, as shown in Figure 21. The axial flow through this section is monitored so as to obtain the average inflow velocity through this section. The average inflow velocity of this section is defined as the actual advance velocity \(V_{A}\) of the propeller [32], and the actual advance velocity \(V_{A}\), the advance coefficient \(J\), the thrust coefficient \(K_{T}\), the torque coefficient \(K_{Q}\), and the propulsion efficiency \(\eta\) of the propeller in the self-homing point state of the hybrid-driven underwater glider at four working conditions of 6 kn, 5 kn, 4 kn, and 3 kn are calculated, as shown in Figure 22.  
As can be seen from Figure 22, the actual advance speed \(V_{A}\), advance speed coefficient \(J\), thrust coefficient \(K_{T}\), and propulsive efficiency \(\eta\) of the propellers of each hybrid-driven underwater glider show a trend of first decreasing and then increasing with the increase in the bending degree of the end plate of the Kappel propellers. However, the propeller torque coefficient \(K_{Q}\) of the hybrid-driven underwater glider shows a monotonically increasing trend with the increase in the bending degree of the propeller end plate. From the analysis of Figure 22a,b, it can be seen that, for the same type of Kappel propeller, the actual advance speed \(V_{A}\) and the advance coefficient \(J\) of the propeller change in the same direction as the speed of the hybrid-driven glider, which is the same as the actual trend of the project. At the same speed, except for the conventional propeller Kap00, the actual advance velocity \(V_{A}\) and the advance coefficient \(J\) of the propeller gradually increase with the increase in the bending degree of the end plate of the series Kappel propeller. The actual advance velocity \(V_{A}\) and the advance coefficient \(J\) corresponding to the propeller Kap05 are the largest, indicating that the increase in the bending degree of the end plate of the Kappel propeller can effectively improve the utilization of the kinetic energy of the convective field of the hybrid-driven underwater glider, and at the same time can reduce the resistance of the hybrid-driven underwater glider in the process of self-propulsion to improve energy efficiency. From the analysis of Figure 22c, it can be seen that, at the same speed, except for the conventional propeller Kap00, the thrust coefficient \(K_{T}\) gradually increases with the increase in the bending degree of the end plate of the series Kappel propeller, indicating that the increase in the bending degree of the end plate of the Kappel propeller can effectively improve the output thrust. For Kappel propellers of the same model, the thrust coefficient \(K_{T}\) is reversed from the speed of the hybrid-driven glider.