# Thermal Characteristics Study of the Bump Foil Thrust Gas Bearing
## 1 Introduction
It was pointed out that the bearing load capacity decreased with the increase in rotating speed when the speed increased to a certain value. This trend was due to the bending deformation of thrust disc caused by the high gas film temperature, which leads to the decrease in gas film thickness and the final thermal runaway [9]. [PERSON] established conduction and convection heat transfer models for the bearing sleeve and rotor of the journal bump foil gas bearing, which coupled the non-isothermal Reynolds equations, gas film energy transfer equations, and foil deformation equations. The simulation results compared the THD model with the isothermal model, analyzed the static characteristics and dynamic characteristics of the gas foil bearing [10]. [PERSON] applied the commercial software to simulate the temperature field of thrust bearing, and studied the influences of different boundary conditions, rotor speeds, inlet pressure, and temperature on bearing thermal characteristics [11]. [PERSON] and [PERSON] simplified the foil structure as a line spring model, considered the forced convection cooling outside the flat foil, calculated the multi-dimensional distribution of gas film temperature, but ignored the heat transfer from temperature to rotor and sleeve [12]. [PERSON]'s research results show that the maximum temperature of the film increases with the grow of load and rotational speed, in which the influence of the rotational speed is greater. At the same time, it is found that the temperature gradient along the axial direction of the rotor can easily cause structural and thermal instability [13]. [PERSON] and [PERSON] found that the viscosity of the gas film increased with the temperature rises, which enhanced the effect of dynamic pressure. The influence of the temperature of the gas film on the structure stiffness of the foil is small. The closer to the shaft end, the greater the gas film temperature gradient, and the axial temperature gradient grew with the increase in the rotational speed [14]. [PERSON] and [PERSON] found that the axial temperature gradient will cause the flat foil warping in the end region of the bearing, resulting in uneven axial distribution of the film gap, which makes the flat foil easy to grind with the rotor [15]. [PERSON] and [PERSON] studied the complete heat transfer in a 50 KW turbine. It was found that the dynamic stiffness and damping coefficient of the bearing would decrease due to the decrease in the elastic modulus of the foil structure at high temperature [16]. [PERSON] and [PERSON] et al. heated the rotor without cooling gas flow, and the bearing failure occurred when the rotor temperature reached 251 \({}^{\circ}\)C [17]. Therefore, the heat control and temperature control strategies, such as injectingcooling gas flow in high temperature environment are very necessary. In this study, a detailed 3D thermal model of bump foil thrust gas bearing is considered. The temperature field distribution of the thrust bearing is solved by coupling the three-dimensional energy equation, non-isothermal Reynolds equation and gas film thickness equation. The cooling models of foil structure and thrust plate, as well as the influence of temperature on the thermal expansion of bearing structure are considered. The thermal characteristics of the bearing under different working conditions are analyzed. Finally, the test rig of the foil thrust gas bearing is built to measure the bearing temperature distributions of bearing under different working conditions.