In modern turbo-machinery gas journal bearings have been increasingly adopted, because they can operate at higher speed than most bearing designs. The main disadvantage of gas bearings is their low dynamic stability range. One solution to improve this and their performance is to combine the aerodynamic effect with the addition of external pressurization in a hybrid gas bearing. This study uses a mathematical model for hybrid lubrication of a compressible fluid film journal bearing with adjustable control of the external pressure, developed previously in . The model is based on a compressible form of Reynolds Equation. To include the effect of the injection, an extra term is added to the Reynolds Equation, considering the fully developed Hagen-Poeiseuille flow in the injection pipeline. In order to verify this assumption, a Computational Fluid Dynamics (CFD) model is developed and the pressure and velocity fields in the injection nozzle are compared. The simplified theoretical model has been validated against the CFD results and experimentally using a test rig. The test rig consists of a flexible rotor supported by a ball bearing and a controllable hybrid gas bearing. The results show that the level of pressure has a strong influence in the dynamic behavior of the system, and with the correct level of pressure and different pressurization strategies it is possible to improve the dynamic performance of the system.
12th Edf - Pprime Workshop: “solutions for Performance Improvement and Friction Reduction of Journal and Thrust Bearings”, 2013
Gas bearings; Dynamic performance; Damping factor; Pressure adjustment; Modal analysis