## 6 Conclusions  
The research in this paper conducts measurement experiments on the relevant features of the physical field of underwater thermal jets using PIV and PLIF techniques. Additionally, this paper performs numerical calculations using simulation software to compare the effects of different factors on the temperature diffusion of the jet. From the analysis of various influencing factors, this paper has drawn the following conclusions:  
1. When the velocity of the jet increases, the diffusion of the jet temperature is primarily driven by horizontal movement. Initially, there is minimal upward floating at the onset of the jet discharge. However, as time progresses and the jet flow decays, the jet temperature begins to diffuse upwards. Overall, the horizontal temperature diffusion  
Figure 19: Simulation calculated results of the thermal jet temperature field.  
is predominantly influenced by the jet velocity. Ultimately, the jet temperature is unable to diffuse all the way to the water surface. Furthermore, an increase in jet velocity hinders upward diffusion of its temperature while a decrease in floating height slows down the decay rate of its temperature.
2. As the temperature difference of the jet increases, upward levitation dominates the jet temperature diffusion, resulting in a 40-50% enhancement in the levitation rate. However, there is no significant change in the temperature decay rate. Prior to the diffusion of the jet temperature to the water surface, the temperature difference between the main body of the jet and the surrounding water decreases to within 2-4 \({}^{\circ}\)C. Once the jet temperature spreads to the water surface, a lateral temperature diffusion region forms near the water surface, leading to more noticeable temperature dissipation.
3. The impact of background environmental stratification on the diffusion of the jet temperature is significant. When the jet temperature diffuses to the stratification interface, it stops floating due to density differences and cannot diffuse to the water surface. As a result, the lateral diffusion area near the stratification interface experiences an increase in the jet temperature. The environmental stratification status inhibits the floating diffusion of the jet temperature, thereby reducing its rate of diffusion.  
In fact, this paper simplifies the problem of submarine cooling water discharge into a static thermal jet problem for research and analyzes the differences of jet floating diffusion in a strongly stratified environment. Based on the changes in jet velocity and depth, relevant suggestions can be given on whether there is a risk of infrared exposure on the surface of the water, and it is necessary to pay attention to the characteristics of the stratified state of the marine environment during the actual voyage of the submarine to ensure that the temperature signature of its discharged jet is not detected. The simplification of this study has brought about some problems, one is that the jet discharge process under the motion state is not simulated, the other is that the submarine model or the actual submarine is not studied. In the follow-up work, it can be further discussed.  
Conceptualization, C.G. and Y.D.; methodology, C.G. and F.L.; software, C.G.; validation, C.G. and B.W.; formal analysis, C.G.; investigation, C.S.; resources, C.S.; data curation, C.G.; writing--original draft preparation, C.G.; writing--review and editing, C.G.; visualization, C.G.; supervision, C.S.; project administration, C.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Approved for publication after confidential review (2024-2639).  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.