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Description:
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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 . |