Experimental versus theoretical characteristics of a high-speed hybrid (combination hydrostatic and hydrodynamic) bearing

The high-speed test facility designed and installed at Texas A&M to study water lubricated journal bearings has been successfully used to test statically an orifice compensated five-recess-hybrid (combination hydrostatic and hydrodynamic) bearing for two radial clearance configurations. Measurements of relative-bearing position, torque, recess pressure, flow rate, and temperature were made at speeds from 10,000 to 25,000 rpm and supply pressures of 6.89 MPa (1,000 psi), 5.52 MPa (800 psi), and 4.14 MPa (600 psi). For speeds of 10,000 and 17,500 rpm, the bearing load capacity was also investigated. A pitching instability of the bearing limited the number of test cases. A 2-dimensional, bulk-flow, Navier-Stokes numerical analysis program was used for all theoretical performance predictions. Orifice discharge coefficients used in the program were calculated from measured flow and pressure data. Reynolds numbers for flow within the bearing lands due to shaft rotation and recess pressurization ranged from 6700 to 16,500. Predictions sensitivity to ±10 percent changes in the input parameters was investigated. Results showed that performance prediction sensitivities are high for changes in discharge coefficients and negligible for changes in relative roughness. The numerical predictions of relative bearing position, recess pressure, flowrate, and torque are very accurate, provided the selected orifice discharge coefficients are correct.