动载荷作用下的轴颈涡动与滑动轴承瞬态油膜力耦合机制研究

Coupling mechanism analysis between shaft whirling and transient oil film force of journal bearings under dynamical load

滑动轴承瞬态油膜力既是转子-轴承系统阻尼的主要来源,也是导致机组稳定性下降的重要原因。针对大扰动下的动网格更新问题,采用一种适用于固定瓦轴承的新型结构化动网格技术,建立了动载荷作用下滑动轴承非线性瞬态油膜力的CFD模型,该模型中采用“全空化模型”描述润滑介质的空化。针对圆柱形轴承和多油楔滑动轴承分析了轴颈涡动与瞬态油膜力之间的相互作用机制。结果表明:非线性油膜力支撑下,计算得到静平衡位置结果与试验结果的偏差小于2.5%,说明了该模型可以较为准确的描述转子-滑动轴承系统;非线性油膜力支撑下,动载荷对于转子稳定性有明显影响,当动载荷较小时,在轴颈涡动过程中油槽会严重削弱径向、切向油膜力;随着动载荷的增加,油槽的作用减小,径向、切向油膜力逐渐增加,进而抑制半速涡动;对于多油楔滑动轴承,油槽的影响相对较小,故而油膜力可以提供足够的刚度和阻尼,以保持较高的稳定性。

Transient oil film force is the main damping source of a rotor-bearing system,and also an important reason for instability.Firstly,a new structured dynamic mesh method was presented for mesh updating.Based on this method,a CFD model for nonlinear transient oil film force under dynamical load was established.The cavitation was described by the"full cavitation model".Then the coupling mechanism between shaft whirling and transient oil film force was analyzed for circular and multi-wedge journal bearings.Results indicate that the deviation between the calculated results of the static equilibrium position and the experimental results is less than 2.5%.Under the support of nonlinear oil film force,the dynamic load has an obvious influence on the stability of the rotor.When the dynamic load is small,the oil tank seriously weakens the radial and tangential oil film force in the shaft whirling process.With the increase of dynamic load,the influence of the oil wedge decreases,the radial and tangential oil film force increase gradually,and the half speed whirling can be suppressed.For multi-wedge bearings,the influence of the oil tank is relatively small,so the oil film force can provide enough stiffness and damping to maintain stability.