Axial Oil Film Rupture in High Speed Journal Bearings and Its Effect on the Rotordynamic Coefficients.

设计并制造了高速滑动轴承轴向膜破裂试验装置。安装在测试轴承上的电容式间隙传感器用于检测膜的破裂。利用该试验台，发现滑动轴承高速运行导致轴向膜破裂的发生。建立了预测轴向膜破裂行为的理论模型。该数学模型是一个修正的雷诺方程，它考虑了传统润滑理论认为作用在支承膜上的离心力的影响，而离心力的影响可以忽略不计。实际上，由于高旋转操作，它对于高速滑动轴承来说并不小。当膜压力因离心力而降低时，分解空气出来并在膜内聚结，导致轴向膜破裂。由于轴颈的高速旋转，可以合理地假设轴颈的偏心比几乎为零，然后将计算域简化为由膜厚和轴承轴定义的二维平面。得到了轴承长径比、间隙比、供油压力等不同设计变量的影响。得到了轴颈在平衡状态下的小位移或小速度时部分破裂油膜的转子动力系数。分析了高速浮套轴承支承下的Jeffcott转子的稳定性图，发现该理论模型能够合理地解释实际机械的振动现象。

A test rig was designed and made to investigate axial film rupture in high speed journal bearings. Capacitance-type gap sensors installed in the test bearings were used to detect the film rupture. With this test rig, it was found that high speed operation of journal bearings resulted in the occurrence of axial film rupture.A theoretical model was derived to predict the behavior of the axial film rupture. This mathematical model is a corrected Reynolds Equation which incorporates the effect of centrifugal force acting on the libricating film which conventional lubrication theories assume to be negligibly small. Actually it is not small for high speed journal bearings due to high rotational operation. When the film pressure decreases due to the centrifugal force, resolved air come out and coalesce in the film, resulting in axial film rupture. The eccentricity ratio of the journal can be reasonably assumed to be nearly naught because of very high speed rotation of the journal, then the calulation domain can be reduced to a two dimensional plane defined by the film thickness and the bearing axis. The effects of various design variables, such as bearing length to diameter ratio, clearance ratio, supply oil pressure and so on, were obtained.The rotordynamic coefficients of the partially ruptured oil film were obtained for small displacements or small velocities of the journal at equilibrium in the bearing. The stability charts for a Jeffcott rotor supported in high speed floating bush bearings were analyzed, and this theoretical model were found to reasonably explain the vibration phenomena of actual machines with the bearings.