The high temperature cooling water generated by the power system of underwater vehicle is discharged through the discharge port and mixed with seawater to form a thermal wake, whose thermal characteristics can be easily detected by infrared submersible technology. In order to explore the characteristics of the thermal wake of the underwater vehicle when it rotates in fresh water, this paper uses the finite volume method to establish a three-dimensional scaled SUBOFF mathematical model, and then combines the overlapping grid technology to numerically simulate the rotation of the underwater vehicle in the background waters. The thermal wake experimental platform is established to verify the reliability of the numerical simulation method by comparing the direct flight experiment with the simulation results. The near-field cooling water trajectory and far-field wake spatial evolution behind the rotary body are analyzed, and the abnormal characteristics of water surface temperature are obtained. The results show that the thermal wakes on the turning side and the deviation side are greatly affected by the vortex caused by the body, and have great differences in morphology, motion trajectory and temperature characteristics. When the thermal wakes on both sides rise to the water surface, an arc-shaped water surface temperature anomaly area composed of two high-temperature hot spots is formed.

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In order to explore the rising and diffusing path of an underwater thermal jet and the temperature variation of each water layer in the typical ocean thermohaline stratified environment, a three-dimensional mass-heat transport model of the thermal jet in a weak stratified environment was built by using the Detached-Eddy Simulation method and Volume of Fluid model to simulate the whole life evolution process of the thermal jet in different depths, temperature difference, and flow rate. A series of characteristic parameters were constructed to quantitatively evaluate the temperature change of the water layer caused by the thermal jet. The results show that the disturbance of the thermal jet on the environmental water body will lead to a change in the distribution of the isothermal layer. Under the combined influence of thermal conduction, thermal convection, and entrainment, thermal signals, cold–thermal mixing signals, or cold signals may appear in different water layers, and the boundary distribution and range of the water layer are decided by the jet parameters and the relative position between the jet and water surface.

The heat and mass transfer process of the laminar falling liquid film along a vertical heated plate with constant heat flux is studied. Through thermal equilibrium analysis, the energy conservation equation is established and solved by the parametric variation method. The analytical solution considering evaporation is in good agreement with the experimental results. Based on the model, the temperature distribution of liquid film with or without evaporation is obtained. It is demonstrated that the thickness and average temperature of liquid film show decreasing and increasing trends linearly in the flow direction. Along with the increase in the evaporation rate, the average temperature decreases and the share of evaporative heat dissipation in the total heat flux increases, which demonstrates that evaporation is an important physical factor for heat dissipation when the falling liquid film flows on a hot plate.