## 4 The Simulation Comparison of the Oval Discharge Port  
In the spatial dimension, a three-dimensional cartesian coordinate system is established with the center of the discharge port as the origin, the flow direction of the environmental fluid as the negative direction of the X-Axis, the discharge direction of the thermal jet as the positive direction of the Y-Axis, and the gravity direction as the negative direction of the Z-Axis. The radius of the oval discharge port is distributed along the X-Axis and Z-Axis. The radius ratio is defined as the ratio of the oval discharge port radius in the Z-Axis to the oval discharge port radius in the X-Axis. Table 1 shows the structural parameters of the oval discharge port with different radius ratios. The structure of the oval discharge port is shown in Figure 3.  
Figure 3: Structure diagram of different radius ratios of oval discharge ports. Figure 2: Grid independence test. Figure 4 shows the flow track of a thermal jet discharging from a circle discharge port. Under the influence of environmental water movement, the cooling water displays the flow separation phenomenon after discharging from the discharge port and forms two thermal jets. One thermal jet floats faster in the Z-Axis direction but has a smaller movement distance in the Y-Axis direction. The other thermal jets have a lower buoyant height but a longer discharge distance. Figure 5 shows the fluid movement near the discharge port. When the inflow is mixed with the cooling water, a vortex movement is formed behind the discharge port. Due to the high temperature and fast speed of the thermal jet, there is a pressure difference between the thermal jet and the environmental water behind the discharge port. Thus, fluid movement is formed behind the discharge port, and it is completely opposite to the inflow direction. Therefore, the cooling water forms two thermal jets with different motion states after discharging. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Discharge Port** & **X-Axis Radius/m** & **Z-Axis Radius/m** & **Radius Ratio** \\ \hline Str 1 & 0.004 & 0.025 & 4:25 \\ Str 2 & 0.005 & 0.02 & 1:4 \\ Str 3 & 0.008 & 0.0125 & 16:25 \\ Str 4 & 0.01 & 0.01 & 1:1 \\ Str 5 & 0.0125 & 0.008 & 25:16 \\ Str 6 & 0.02 & 0.005 & 4:1 \\ Str 7 & 0.025 & 0.004 & 25:4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Structure parameters of different radius ratios of oval discharge ports. Figure 4: Flow streamline of the thermal jet from the circle discharge port. Figure 5: Local velocity vector diagram of the thermal jet from the circle discharge port. The dimensionless temperature difference \(\theta\) is defined as \(\theta=(T-T_{0})/(T_{1}-T_{0})\), where \(T\) is the maximum temperature at the center of the thermal jet, \(T_{1}\) is the initial temperature of the thermal jet and \(T_{0}\) is the temperature of the environmental water. Figure 6 shows the variation trend of \(\theta\) of the thermal jet at the circle discharge port along the X-Axis and Z-Axis. The thermal jet diffuses in the negative direction along the X-Axis under the influence of the motion of environmental water. In the X-Axis direction, the temperature of the thermal jet decreases the fastest, especially in the initial section. Within 0.06 m from the center of the discharge port, the temperature of the thermal jet decreases 22 K, and the total temperature attenuation distance of the thermal jet in the X-Axis is 2.855 m. The temperature  
Figure 6: Temperature attenuation indicatrix of the thermal jet from the circle discharge port: (a) X-Axis; (b) Z-Axis. attenuation distance increases by 0.12 m for every 1 K of temperature attenuation in the middle section of the thermal jet and by 0.71 m for every 1 K of temperature attenuation in the rear section of the thermal jet. With the increase in the thermal jet temperature attenuation distance along the X-Axis, \(\theta\) gradually tends towards 0.