# Effect of Thermal Boundary Condition on Tilting Pad Journal Bearing Behavior
###### Abstract
From 16% to 25%, decreased bearing clearance was measured at a hot temperature condition compared to room temperature. Thermal expansion of journal and bearing were measured and predicted. [PERSON] and [PERSON] [19; 20] presented a high-fidelity TPJB numerical model with a TEHD lubrication model. Both elastic and thermal deformation of bearing pad were predicted by 3D FE model adopting nonlinear transient dynamic analysis. Hertzian contact theory was used to predict the pivot elastic deformation. [PERSON] [21] predicted the journal bearing performance with the consideration of thermal and cavitation effect using CFD approach with fluid structure interaction (FSI) model, and the predictions were compared with the published results of other researchers. [PERSON] et al. [22] predicted a journal bearing temperature using ANSYS Fluent. [PERSON] et al. [23] studied the effects of supply flow rate of lubricant on bearing static and dynamics characteristics at steady state condition. [PERSON] et al. [24] studied the effects of geometrical defects of a two-lobe journal bearing on system temperature. [PERSON] and [PERSON] [25] performed an experimental test to study the misalignment effect on plain journal bearing performance. Pressure, oil temperature, oil flow rate, and minimum film thickness were measured at various misalignment conditions. [PERSON] and [PERSON] [26] studied the performance of a misaligned TPJB under unsteady loading condition, adopting a TEHD lubrication model. Both elastic and thermal deformations of bearing pads were considered, and a film thickness equation was newly developed to take the misaligned condition into account. [PERSON] and [PERSON] [27] developed a 3D FE model of TPJB to study the angular misalignment effect. FE node-based film thickness equation was developed. Minimum film thickness, pad thermal deformation, bearing performance, and lubricant peak temperature were simulated with varying amount of misalignment. [PERSON] et al. [28] performed an experimental test and studied the effect of high-temperature inlet oil on the TPJB characteristics. Oil film thickness, temperature rise, and the rotor dynamic behavior under different inlet temperature were tested and compared. [PERSON] and [PERSON] [29] studied bearing side leakage flow and utilized an empirical coefficient to provide the efficient bearing oil feeding configuration. [PERSON] and [PERSON] [30; 31] presented a full 3D computation numerical model of TPJB with the consideration of multiphase flow, turbulence effects, and thermal expansion of the spinning journal and bearing pads using a two-way FSI model. Detailed comparisons between the CFD and the Reynolds approach were performed. They accurately analyzed the phenomenon of lubricant mixing between pads and entering the pads using 3D CFD technique, but it is limited in application to the actual bearing design due to excessive analysis resources. [PERSON] et al. [32] presented a 3D TPJB model based on the commercial multi-physics software COMSOL. Their research was oriented to the rotordynamic behavior of the bearing-rotor system. On the other hand, there have been other approaches to overcome the bearing performance adopting the active control unit in the journal bearing system [33; 34]. In addition to the references mentioned above, a number of numerical analysis models for bearings have been developed so far. However, there have been no in-depth studies related to the performance change according to the change of the thermal boundary conditions of the bearing-journal system. This is due to the difficulty in modeling the heat transfer of bearing pads and journals and predicting the resulting thermal deformation. The axial thermal boundary condition of the journal cannot be taken into account with the 2D bearing model that has been presented in the earliest studies. In addition, it is difficult to predict the exact performance of bearings with the simplified bearing model suggested by most researchers.