A Model for Oil Flow and Fluid Temperature Inlet Mixing in Hydrodynamic Journal Bearings

The quality of predictions for the operating behavior of high-speed journal bearings strongly depends on realistic boundary conditions within the inlet region supplying a mixture of hot oil from the upstream pad and fresh lubricant from the inlet device to the downstream located pad. Therefore, an appropriate modeling of fundamental phenomena within the inlet region is essential for a reliable simulation of fluid and heat flow in the entire bearing. A theoretical model including hydraulic, mechanical, and energetic effects and the procedure of its numerical implementation in typical bearing codes for thermo-hydrodynamic lubrication is described and validated. Convective and conductive heat transfer as well as dissipation due to internal friction in the lubricant is considered for the space between pads or the pocket where the inlet is located. In contrast to most other models, the region between the physical inlet and the lubricant film is part of the solution domain and not only represented by boundary conditions. The model provides flow rate and temperature boundary conditions for extended Reynolds equation and a three-dimensional (3D) energy equation of film and inlet region, respectively. The impact of backflow from the inlet region to the outer supply channel possibly occurring in sealed pockets is taken into account. Moreover, the model considers the influence of turbulent flow in the inlet region.