On the Performance of Hydrostatic Journal Bearings in Air, Water, and Liquid Nitrogen: Measurements and Predictions

Abstract

Turbopumps in reusable and low-cost liquid rocket engines require compact and simple hydrostatic (i.e., externally pressurized) bearings to support large static and dynamic loads at high shaft speeds with no bearing DN (diameter in millimeters times rpm) life limitation. Hydrostatic bearings are one of the key mechanical components for cryogenic turbopumps to improve their reliability and reusability. Hydrostatic bearings offer significantly enhanced durability with very low friction and wear while providing accurate rotor positioning as well as large load and static stiffness characteristics even working with low-viscosity liquids. This work measures static load characteristics of hydrostatic journal bearings in air (25 degrees C), water (from 25 degrees C to 70 degrees C), and liquid nitrogen (-197 degrees C). Air, water, and liquid nitrogen are used as test fluids for the test bearing to evaluate the effects of fluid properties and temperatures on the bearing performance. A complete set of applied static load, bearing eccentricity, and bearing supply pressure for each test fluid (i.e., air, water, and liquid nitrogen) is presented for the test hydrostatic bearing. Measurements show that the applied static load on the test bearing significantly affects the recorded journal eccentricity ratio, bearing flow rate, and bearing static stiffnesses. Predictions are in good agreement with measurements. The predictable performance of hydrostatic journal bearings in air, water, and liquid nitrogen can further their application in various cryogenic turbopumps for liquid rocket engines.