Effect of recess pressure ratio on the characteristics of a hybrid bearing

Abstract

Hybrid (Combination Hydrostatic and Hydrodynamic) bearings have shown good properties in testing and in consideration for applications such as the Space Shuttle Main Engine High Pressure Oxygen Turbopump. However, properties have not been examined for a variation in the design parameters of radial clearance, recess pressure ratio, and recess to land area ratio while holding the other parameters constant. This thesis presents the theoretical and experimental characteristics for an orificecompensated, annulus-fed hybrid water journal bearing for variation in recess pressure ratio. Recess pressure ratio Pr is defined as [ ] where Pr is the recess pressure, P, is the supply pressure, and Pa is the discharge pressure. Rowe (1983) showed that the bearing load capacity can be maximized by a Pr value of 0.58 at the concentric position for hydrostatic bearings. Experimental results showed the maximum load capacity to bear near 0.58 with slight variation as rotor speed and supply pressure are varied. Test results show that maximum stiffness occurs over a range of Pr from 0.4 to 0.7 with variation in operating speed and supply pressure. The direct damping increases as recess pressure ratio is decreased. Whirl frequency ratio and torque show little variation with recess pressure ratio. Predictions are made using HYDROBEARC developed by San Andres (1992). Accuracy of prediction is analyzed by comparison with experimental test results and found to be adequate, with decreasing accuracy as supply pressure and especially rotor speed are increased. Previous work found the accuracy of prediction by HYDROBEARC to increase as the rotor speed is increased.