The inlet pressure build-up at the leading edge of bearings and its effects on the bearing performance are investigated both theoretically and experimentally. In order to evaluate the inlet pressure correctly, the full Navier-Stokes equations are solved numerically for the computational domain with covers the cavity region between pads as well as the bearing film. A nonuniform grid system is adopted to reduce the number of grid points, and the numerical solutions are obtained for a wide range of Reynolds number in laminar regime with various values of distance between pads. The numerical results show that the inlet pressure is significantly affected by Reynolds number and the distance between pads. An expression for the loss coefficient in terms of Reynolds number and non-dimensional distance between pads in obtained on the basis of the numerical results. It is found that the inlet pressure over the whole range of numerical solutions can be fairly accurately estimated by applying the formula for the loss coefficient to the extended Bernoulli equation.
The performance analyses of inclined slider bearings, sector-shaped thrust bearings and tilting-pad journal bearings are carried out using the inlet pressure, which is obtained by means of the formula for the loss coefficient, as a boundary condition for the oil film pressure. The results show that there can be remarkable difference in the inlet pressure depending on the method used to evaluate the inlet pressure, and that there is a significant influence of the inlet pressure on the performance of those bearings.
Experiments are conducted to verify the validity of the theoretical result. The test apparatus consists of one or two tilting pads and rotating cylinder. Oil film thickness, oil film pressure in the mid plane and the inlet pressure distribution are measured for various operating conditions. The experimental results are compared with the theoretical results which are obtained by means of several methods evaluating the inlet pressure, and it is found that the method established in this thesis can predict the inlet pressure more accurately and is useful for design purpose.
