# Simulation Study on Thermal Wake Characteristics of Underwater Vehicle under Rotary Motion
## 1 Introduction  
As an important strategic weapon, the underwater vehicle has the advantage of good concealment and plays an extremely important role in spatial three-dimensional warfare [1]. When the underwater vehicle is sailing, most of the heat generated by the nuclear reactor will be released into the seawater, resulting in a thermal wake behind the body that is difficult to disappear, and the thermal wake will rise to the ocean surface to form hot spots of high temperature [2]. With the development of infrared submarine exploration technology in the military field, the temperature difference of 0.001 \({}^{\circ}\)C on the ocean surface can be detected, which undoubtedly greatly reduces the concealability of underwater vehicles [3]. A lot of theoretical and experimental research has been carried out on the thermal wake of underwater vehicles. In [4], the author took the cooling water as a floating jet with momentum and studied the motion track and attenuation characteristics of the hot jet in uniform and stratified flow. In [5], the author adopted particle tracking technology to realize flow field visualization and observed the motion trajectory of underwater vehicle wake. In [6; 7; 8; 9], the author studied the turbulent wake generated by underwater momentum disturbance, underwater sphere, surface ship and submarine, and systematically revealed the formation process of thermal wake and the change law of wake velocity and temperature. In [10], the author analyzed the interaction between turbulent vortex and water surface caused by wake evolution and obtained the changes of velocity field and turbulent kinetic energy field on free surface. Domestic scholar [PERSON] [11] took the lead in establishing the thermal wake measurement platform. Then, under the conditions of geometric similarity,similar heat flow and similar temperature field, [PERSON] [12], [PERSON] [13] and [PERSON] [14] successively conducted thermal wake infrared detection experiments of underwater vehicles under direct navigation conditions. The floating process of thermal wake is divided into near wake section, transition section and far wake section. Domestic and foreign scholars on the numerical simulation of underwater vehicle thermal wake mainly focus on the numerical simulation method, wake formation mechanism, floating diffusion and temperature attenuation law, surface infrared characteristics of influencing factors and so on. In [15], the author obtained the distribution of wake velocity field of underwater vehicle under rotating condition by numerical calculation. In [16], the author used the LES numerical simulation method to observe the vortex structure of wake evolution. Domestic scholars [PERSON] [17], [PERSON] [18] and [PERSON] [19] conducted two-dimensional simulation on the thermal wake emission of underwater vehicles under direct navigation condition. [PERSON] [20], [PERSON] [21] and [PERSON] [22] conducted three-dimensional simulation on the thermal wake emission of underwater vehicle under direct navigation condition to simulate the three-dimensional vortex structure of wake. The floating diffusion process and surface temperature characteristics of thermal wake are analyzed. [PERSON] [23] adopted the inflow method, [PERSON] [24] adopted the overlapping grid method, and [PERSON] [25] used four numerical methods to simulate the floating of underwater vehicle's thermal wake. Through qualitative and quantitative analysis, the following results were obtained: drainage method and slip grid method strengthened the energy and mass transfer process. The overlap grid technology and moving grid technology strengthen the temperature characteristics of wake flow. In [26], the author numerically simulated the rotation condition of the underwater vehicle and obtained the velocity distribution and vortex morphology of the flow field. In [27; 28; 29], the boundary conditions and water environment also had certain influences on jet entraining.