Large tilting pad journal bearings are widely used in large and high speed applications such as large steam or gas turbines, owing to their inherent stability characteristics. However, there exist much discrepancies in the bearing performance between the theoretical prediction and measurements, mainly because of the difficulty to select the pressure and temperature boundary conditions for large tilting pad journal bearings. In this thesis, the static and dynamic performance of large tilting pad journal bearings are investigated theoretically and experimentally. The thermohydrodynamic characteristics are analyzed, taking into account the effects of three dimensional variation of lubricant viscosity, turbulence and inlet pressure. The stiffness and damping coefficients are obtained by means of small perturbation method. The effects of the temperature rise, turbulence and inlet pressure on the bearing performance are studied in comparision with the isothermal or the laminar analysis. It is observed that these effects have significant influences not only on the static characteristics such as the temperature distribution, load capacity and frictional force, but also on the stiffness and damping coefficients of the large tilting pad journal bearing. The experiments are performed in order to verify the validity of the theoretical result and, in addition, to investigate the thermohydrodynamic performance of large tilting pad journal bearings. The continuous film pressure, film thickness and shaft surface temperature, and bearing surface temperature are measured along with the shaft speed and the bearing load for various flow rates of the labricant. Considerably large inlet pressure is observed at the entrance of each pad, especially lower pads. The inlet pressure increases with the increase in shaft speed as well as bearing load, but is almost independent on the flow rate. The upper pads always keep up slight wedge film shape owing to the inlet pressure, and scraping is not observed in the upper pads. It is observed that the shaft surface temperature is uniform in the circumferential direction and increases with the increase of shaft speed in both low and high shaft speed region, however, there exists transition region where the shaft surface temperature decreases with the increase in shaft speed. The flow rate has a significant influence on the distribution of the bearing surface temperature and the critical speed at which the flow transition occurs. The experimental results are good agreement with the theoretical ones which are calculated by the three dimensional turbulent thermohydrodynamic analysis including the inlet pressure effect. In summary, it has been shown that the effects of the temperature rise, turbulence and inlet pressure have significant influences on the performance of large tilting pad journal bearings. Therefore it is suggested that all of these effects must be considered simultaneously in the theoretical analysis in order to predict the performance of the large tilting pad journal bearing more accurately. And it is suggested that the present theory should be useful to predict the performance of large tilting pad journal bearings for electric power plants more accurately.
