Aerostatic and Aerodynamic Performance of an Out-Pump Spirally Grooved Thrust Bearing: Analysis and Comparisons to Static Load Experiments

The combined effects of external pressurization and out-pump spiral grooves are studied according to the incompressible fluid Whipple analysis on spirally grooved gas bearings. The results are examined in terms of non-dimensional parameters that bring out the interaction between the action of spiral groove self-pressurization and external pressurization through orifices. It is found that interaction is beneficial when the supply pressure level to the orifices is near the peak pressure that can be reached by the spiral grooves alone. An optimized interacting design can improve the bearing stiffness and load carrying capacity. However, when the action of spiral groove self-pressurization dominates, the orifices are merely a resistance of inlet because of the strong out-pump action of spiral grooves. On the other hand, when the action of external pressurization dominates, the spiral grooves still add to the bearing stiffness and load-carrying capacity even though the action of the spiral groove self-pressurization is at a low level. The orifice flow tends to be saturated ahead because of the spiral grooves in stationary state and their out-pump self-pressurization in steady state. Out-pump spiral grooving is found to be the preferred configuration to combine aerostatic and aerodynamic actions. These predicted trends are qualitatively substantiated by static load tests without rotation.