Effect of Shaft Whirl and Bearing Base Excitation on Stability of Oil Laminar Flow

It is well known that the shaft whirl and bearibng base excitation are closely related to the oil film stability of a journal bearing. However, the correlation among them is yet not well understood. It was traditionally widely practiced to analyze the stability of a fluid film hydrodynamic journal bearing by means of linearized bearing analysis, which assumed that the equilibrium position of the bearing was the starting point. Accordingly, the critical mass and whirl ration could be determined by perturbing the journal center at a small pace, and hence the stability of the system determined from the journal locus. It should be noted that in the presence of shaft whirl and bearing base excitation, the bearing is usually characterized by nonlinear characteristics. This will lead to considerable effect on the performance of the bearing. Therefore, the effect of the periodical whirl of bearing journal and the displacement excitation of the bearing base on the instability of oil film laminar flow was examined on a specifically designed bearing test rig. The results show that the laminar flow instability of the oil film is accelerated with the increase of the journal eccentricity. At a relatively smaller shaft whirl, the instability of the oil film laminar flow was dominated by the vibration intensity and the low frequency vibration of the bearing. At a relatively larger shaft whirl, the stability of the oil film laminar flow was almost independent of the intensity and frequency of the excitation vibration.