Lift-off performance in flexure pivot pad and hybrid bearings
Mertz, David Hunter
MetadataShow full item record
Three flexure pivot pad bearings (FPBs) with different preloads are evaluated for use in high performance applications by comparing them to a hybrid hydrostatic bearing (HHB). One application of these bearings is in turbopumps for liquid rocket engines. To evaluate bearing performance, the lift-off speed of the shaft from the bearing surface is experimentally determined. Experimental data of lift-off are collected using a circuit running through the shaft and the designed bearing. Other methods for measuring liftoff speeds were attempted but did not yield consistent results. Water is used as a lubricant to simulate a low viscosity medium. In comparison to load-capacity-based predictions for FPBs, the experimental results showed lower lift-off speeds, higher load capacities, higher eccentricity ratios, and lower attitude angles. The bearings? predicted load capacity determined lift-off speed predictions, but the experimental results show no clear trend relating lift-off speed to load capacity. This was for a range of running speeds, with the design speed defined as the final speed in a particular test case. At 0.689 bar supply pressure and for a design speed of 3000 rpm, the HHB showed greater load capacities and lower eccentricities than the FPBs, but the FPBs had lower lift-off speeds and attitude angles. In fact, the FPBs in the load-between-pad orientation outperformed the HHB in the load-on-pocket orientation with lower lift-off speeds for the shaft weight-only case. An increased supply pressure lowered the lift-off speeds in the HHB tests. If the load in the bearing application remains relatively small, a FPB could be substituted for an HHB.