# Effect of Thermal Boundary Condition on Tilting Pad Journal Bearing Behavior
###### Abstract  
This research presents the effect of the thermal boundary condition on the tilting pad journal bearing characteristics. The thermal boundary condition includes the temperature around the bearing pad, spinning journal, and lubricant supply temperature. Change in bearing performance according to the temperature around each element constituting the bearing was analyzed without paying attention to how the actual thermal boundary conditions around the bearing are configured. High fidelity numerical model of tilting pad journal bearing is presented for (1) the analysis of heat generation in the thin film, (2) heat transfer in the lubricant, (3) heat flux flowing into the journal and pad, (4) temperature change in the journal and bearing, (5) the resultant thermal deformation, (6) change in the lubricant film thickness arising from the thermal deformation of journal and bearing pads, and (7) the resulting change in the heat generation in the thin film. To reach the steady state of the bearing-journal system, the Runge-Kutta scheme with adaptive time step is adopted where the dynamic and thermal system are solved simultaneously in multi-physics model. Performance change of the bearing according to three changes: (a) boundary temperature around shaft, (b) boundary temperature around bearing pads, and (c) lubricant supply temperature were investigated. title: 10.390.0001/0001/0001/0001/0001/0001/0001/0001/0001/001/0001/001/0001/001/001/001/0001/001/0001/001/001/001/001/001/001/001/001/001/001/001/00  
The varying viscosity Reynolds equation and energy equation were coupled via temperature-dependent viscosity relation. [PERSON] et al. [5] presented a TEHD-lubrication-approach-based TPJB numerical model with modal reduction technique. [PERSON] and [PERSON] [6] presented a transient response of TPJB considering thermal effects and the resultant thermal deformation of bearing structure. [PERSON] et al. [7] presented 3D FE pad model to perform a time transient analysis of journal bearing system with the pad elastic deformation. [PERSON] et al. [8] presented effects of the thermal-elastic deformation of bearing pads on the TPJB dynamic behavior. [PERSON] et al. [9] presented the bearing thermal effects on the dynamic response under the sudden unbalance status such as blade loss. [PERSON] and [PERSON] [10] calculated a transient response of TPJB with TEHD lubrication model with a dynamic loading condition. [PERSON] and [PERSON] [11] performed a computational fluid dynamic (CFD) analysis of an axially grooved journal bearing with a thermo-hydrodynamic lubrication model. 3D Navier-Stokes equation coupled via the energy equation is adopted to solve for the bearing pressure and fluid film temperature. [PERSON] [12] discussed a TPJB design to reduce the system temperature. [PERSON] et al. [13] presented a TEHD lubrication model for the analysis of journal bearings under the time varying loading condition. The finite element (FE) model was used for solving the Reynolds equation, thermal deformation, and elastic deformation of the bearing pads. [PERSON] et al. [14] presented the experimental results of the effects of oil supply temperature and pressure on the journal bearing performance. [PERSON] et al. [15] developed the direct solution method of the varying viscosity Reynolds equation. Fluid film pressure and the cavitation boundary could be determined without iteration scheme. They developed a simplified one-dimensional (1D) thermal approach based on the 2D numerical model. [PERSON] et al. [16] performed an experimental work to compare leading edge groove TPJB with conventional journal bearings under different running conditions. [PERSON] et al. [17] measured the bearing metal temperatures of TPJB with the configuration of five-pad and load-between-pad (LBP). Temperature was measured at the two loaded bottom pads and thermal behavior was predicted by TEHD lubrication model. [PERSON] and [PERSON] [18] measured a hot and cold clearance at test rig.