## 6 Simulation Analysis of Discharge Multiport  
According to the simulation and experimental results, when the radius ratio of the oval discharge port is 4:25, the perimeter of the discharge port is the largest, the radius in Z-Axis is the smallest, the width of the thermal jet is the smallest and the mixing effect of the thermal jet and the environmental fluid is the best. Therefore, on the basis of the oval discharge port of Str 1, the total area of the discharge port is kept unchanged, the number of the discharge ports is increased, the distribution position of the discharge port is adjusted and the radius ratio of each discharge port should be kept unchanged. The specific structure of the discharge port is shown in Figure 18.  
As can be seen from Figure 19, when the discharge port is located on the side of the underwater vehicle, the coiling and mixing phenomenon occur between the discharge ports, which is not conducive to the rapid decline of the thermal jet temperature. When the two discharge ports are distributed up and down, the momentum loss of the thermal jet is rapid, the velocity loss is large and the mixing effect with the environmental water is poor. The gap between the Str A discharge port is long and narrow, and the thermal jet entrainment phenomenon between the two ports is obvious. Therefore, the  
Figure 19: Flow streamline of the thermal jet from the discharge multiport. Figure 18: Structure of discharge multiport. environmental water cannot enter the gap of the discharge port well and mix with the thermal jet for heat exchange, and it can only contact the thermal jet at the edge. The actual perimeter of the interface for the mixing heat transfer between the thermal jet at the Str A discharge port and the environmental water is 188.268 mm, which is smaller than the perimeter of 241.080 mm at the Str 1 discharge port. The interface between the thermal jet and the environmental water is reduced, and the mixing effect of heat transfer is weakened. When the two discharge ports are distributed in the front and the back, the distance of the thermal jet increases in the initial motion direction, the temperature drops rapidly and the mixing effect with the environmental water is better. The gap between the Str B discharge port is small, and the heat transfer is sufficient when the thermal jet is mixed with the environmental water. The perimeter of the interface for the mixing heat transfer between the thermal jet and the environmental water from the Str B discharge port is 340.973 mm, which is much larger than the perimeter of the interface from the Str A and Str 1 discharge ports. The discharge port area is the same, the discharge velocity is the same and the flow rate is the same, but the perimeter of the discharge port is greatly increased, which improves the mixing heat transfer effect of the thermal jet and the environmental water. The temperature of the thermal jet drops the fastest when the two discharge ports are located on either side of the underwater vehicle. There is no coiling and mixing phenomenon between the discharge ports, which is beneficial for improving the heat transfer effect of mixing the thermal jet with environmental water. The perimeter of the interface for the mixing heat transfer between the thermal jet and the environmental water from the Str C discharge port is the same as that of the interface from the Str B discharge port, and the perimeter of the discharge port increases significantly. In this structure, the entrainment phenomenon of the thermal jet disappears, and only the shunt phenomenon exists. The mixing heat transfer effect is the best, and the thermal jet temperature decays the fastest. However, as the Str C discharge port is distributed on both sides of the vehicle, the thermal jet temperature diffusion region increases, and there are temperature diffusion regions on both sides of the vehicle. Figure 20 shows the variation curves of the thermal jet floating height at each discharge multiport.