Rotordynamic evaluation of a roughened-land hybrid bearing

Abstract

Hybrid bearings (combinations of hydrostatic and hydrodynamic bearings) represent an attractive alternative to ball bearings for use in high-speed cryogenic turbopumps. However, the internally-developed cross-coupled forces can generate instabilitiesand are responsible for a speed limitation of the machine. To reduce the cross-coupledforces and raise the onset speed of instability, the use of deliberately-roughened stators has been proposed, and already successfully tested for liquid "damper" seals. This thesis presents experimental as well as theoretical static and dynamic results for a five-pocket orifice-compensated hole-pattern-land hybrid bearing. Experimental data show a significant improvement in stability compared to a smooth hybrid bearing, resulting in an elevation of the onset speed of instability. Poor correlation is found with a code developed by San Andres (I 994), especially for the direct and cross-coupled stiffness predictions. The use of the Moody friction-factor model is thought to be mainly responsible for these mediocre predictions, since it does not correctly account for the clearance influence on the friction factor.