液膜密封非定常工况下的瞬态特性

Transient characteristics of liquid film seals under unsteady conditions

运行工况的瞬时变化严重影响密封性能。利用Matlab建立密封环端面间隙液膜三维模型,采用有限差分法离散基于JFO空化边界条件的雷诺方程,应用SOR迭代求解液膜压力分布,进一步耦合求解雷诺方程与瞬态动力学方程,分析工况连续变化及压力扰动对密封瞬态特性的影响。结果表明:相比于转速瞬时变化,压力瞬时变化过程中挤压效应对密封性能的影响更为显著,密封端面趋近速度越大,由液膜挤压产生的承载能力越高,端面流体被排出的速度越大;压力瞬时变化易引发静环轴向速度振荡,压差越大,振荡幅值越大;压力扰动情况下,空化率与泄漏量急剧突变后趋于稳定,压力突升相比于压力突降更易恢复稳定状态;摩擦扭矩在变工况过程中平稳变化,无较大幅度波动。

Transient change of the operating parameters has a serious influence on the stability of liquid film seals.Three-dimensional model of sealing clearance was established based on Matlab.Reynolds equation considering JFO cavitation boundary was discretized by finite difference method.SOR iteration was used to solve fluid film pressure distribution.By further solved coupled Reynolds equation and transient dynamic equations,the influence of continuous change of working conditions and pressure disturbance on transient characteristics were analyzed.The results show that squeeze effect of liquid film during transient change of pressure has more significant influence on sealing performance than speed change.The faster approach speed of seal face,the higher carrying capacity of liquid film extrusion and the greater the velocity of the discharge of the end face fluid.Instantaneous change of pressure easily leads to the axial velocity oscillation of stator ring.The greater the pressure difference,the greater shock amplitude.Leakage rate and cavitation ratio has a large disturbance tends to be stable after abrupt mutation in the case of differential pressure disturbance.Pressure rise compared to pressure drop is more easily to restore stable state.Friction torque varies smoothly during the condition changing without significant fluctuation.