Static and dynamic behavior of cryogenically cooled hydrostatic journal bearings for space applications

Externally pressurized cryogenically cooled (using LOX or LH2 as coolant) hydrostatic bearings are being considered as an alternative to the conventional ball bearing system of a cryogenic rocket engine turbopump. Comparing with ball bearing system, hydrostatic journal bearings (HJBs) offer several advantages like, higher load capacity, higher stiffness with low coefficient of friction, good damping characteristic and vibration stability. Because of very low viscosity of cryogenic liquids, compared with oil (as lubricant), modeling of cryogenic HJBs, is complicated by factors like: turbulent fluid film, inertia effect, compressibility and variation of cryogenic liquid properties. In this paper a finite difference based numerical model is presented for prediction of static and dynamic performances of LOX/LH2 lubricated hydrostatic journal bearings. Pressure distribution in the fluid film is obtained by solving relevant Reynolds equation. Dynamic behavior is studied through the determination of stiffness and damping coefficients by using finite disturbance method. Sample results have been presented both for static and dynamic conditions.