# Simulation Study on Thermal Wake Characteristics of Underwater Vehicle under Rotary Motion
## 3 Experimental Verification of Numerical Simulation Method  
The above numerical simulation method is used to simulate the exothermic wake of the underwater vehicle in direct navigation motion. The thermal wake experiment platform of underwater vehicle was built, and the experimental results were compared with the simulation results so as to verify the reliability of the numerical simulation method, and provide theoretical support for the subsequent numerical simulation of rotary motion of underwater vehicle. The experimental platform is mainly composed of a thermal wake generator and measuring device. The thermal wake generator is mainly composed of an underwater vehicle scale model, experimental tank, trailer system and cooling water discharge system. Figure 5 shows the experimental model of an underwater vehicle, the size of which is consistent with the simulation model in Table 1. Figure 6 shows the experimental pool, and Figure 7 shows the cooling water discharge device, which is fixed on the electric trailer. Thus, the experimental simulation of an underwater vehicle discharging cooling water is realized. Figure 4: Grid-independence verification. Figure 5: Experimental model of underwater vehicle. Figure 6: Experimental pool. The thermal wake measuring device is composed of an infrared water surface detection system and a wake display system. As shown in Figure 8, a Ferrier high-precision infrared thermal imager is used to conduct thermal imaging on the water surface to observe the temperature distribution of the water surface, and a magenta staining agent is used to observe the trajectory of the thermal wake for high-temperature hot water. Figure 9 shows the water surface temperature field obtained by infrared thermal imager and numerical simulation software when the underwater vehicle is at a speed of 0.1 m/s and a time of 90 s. By comparison, when the hot wake floats to the surface of the water, the surface temperature anomaly area obtained by the experiment and simulation has a high similarity in shape and size. Both of them are composed of two discontinuous high temperature hot spots. The area of the high temperature anomaly area decreases with the increase in the horizontal distance from the underwater vehicle, and there is a low temperature narrow area in the middle. In order to verify the accuracy of the simulation, the thermal characteristics of the abnormal water surface temperature area were quantified, intercept line AB at the center of the pool and the temperature distribution curve of line AB in Figure 9 was obtained. As shown in Figure 10, the temperature distribution curves of straight-line AB obtained  
Figure 8: Infrared thermal imager. Figure 7: Cooling water discharge device. Figure 9: Comparison of water surface temperature field. by experiment and simulation are all saddle-shaped, which proves the existence of a low-temperature narrow area. The width of the abnormal area of water surface temperature measured by experiment is 1.3 m, and the width obtained by simulation is 1.1 m, the deviation is 0.2 m, and the relative error is 15.4%. The peak temperature in the abnormal area of water surface temperature difference measured by experiment is 295.1 K, and the peak temperature obtained by simulation is 295.175, with a deviation value of 0.025 K.  
As shown in Figure 11, the floating trajectory of thermal wake obtained by experiment and simulation has a high consistency in floating Angle and floating form. It can be seen that the cooling water, after ejection from the outlet, has a downward velocity component, and then begins to float backward and upward under the influence of buoyancy to develop into a disorderly turbulent motion, and the farther the distance from the underwater vehicle, the greater the upper and lower width of the thermal wake.