Static and Dynamic Characteristics for a Pressure-Dam Bearing

摘要

Measured rotordynamic force coefficients (stiffness, damping, and added mass) and static characteristics (eccentricity and attitude angle) of a pressure-dam bearing are presented and compared to predictions from a Reynolds-equation model, using an isothermal and isoviscous laminar analysis. The bearing's groove dimensions are close to the optimum predictions of Nicholas and Allaire (1980, "Analysis of Step Journal Bearings-Infinite Length and Stability," ASLE Trans., 22, pp. 197-207) and are consistent with current field applications. Test conditions include four shaft speeds (4000 rpm, 6000 rpm, 8000 rpm, and 10000 rpm) and bearing unit loads from 0 kPa to 1034 kPa (150 psi). Laminar flow was produced for all test conditions. A finite-element algorithm was used to generate solutions to the Reynolds-equation model. Excellent agreement was found between predictions and measurements for the eccentricity ratio and attitude angles. Predictions of stiffness and damping coefficients are in reasonable agreement with measurements. However, experimental results show that the bearing has significant added mass of about 60 kg at no-load conditions, versus zero mass for predictions from the Reynolds-equation model and 40 kg using Reinhardt and Lund's (1975, "The Influence of Fluid Inertia on the Dynamic Properties of Journal Bearings," ASME J. Lubr. Technol, 97, pp. 159-167) extended Reynolds-equation model for a plain journal bearing. The added mass quickly drops to zero as the load increases. Measured results also show a whirl frequency ratio near 0.36 at no-load conditions; however, a zero whirl frequency ratio was obtained at all loaded conditions, indicating an inherently stable bearing from a rotordynamics viewpoint.