螺旋槽液膜密封端面空化发生机理

Cavitation mechanism of spiral groove liquid film seals

液膜中空化的发生直接影响着密封流体动压润滑性能,基于质量守恒的JFO边界条件,建立考虑表面粗糙度的螺旋槽液膜密封物理模型,经坐标变换将不规则物理域转换成规则计算域,采用有限控制体积法离散控制方程并求解,分析了膜厚、表面粗糙度、螺旋槽功用(上游泵送和下游泵送)、螺旋槽开槽位置及空化压力对液膜中空化发生的影响。结果表明:较小膜厚工况易促生空穴,而较大膜厚易削弱空穴,且随着膜厚增大,表面粗糙度的影响降低甚至被忽略;当密封为上游泵送型时,空穴区周向宽度明显大于下游泵送型,而螺旋槽位置对空化的影响与螺旋槽功用密切相关;选取较小空化压力使空穴缩减,而较大者反之,且后者对提升液膜承载有利。

Cavitation occurrence in liquid film has a direct impact on hydrodynamic lubrication performance of mechanical seals. A physical model of liquid film seal in spiral grooves was built with consideration of surface roughness and the JFO cavitation boundary condition on mass conservation. The anomalous physical domain composed of spiral curves was transformed into an inerratic computational domain by coordinate transformation. Finite control volume method was adopted to discretize the liquid film governing equation and the Gauss-Seidel relaxation iterative algorithm was used to solve the algebraic iterative equation. The cavitation occurrence in liquid film was analyzed by multiple factors of liquid film thickness, surface roughness, upstream/downstream pumping function, grooving position of spiral groove and cavitation pressure. Results show that cavitation occurrence was easily strengthened at thin films but weakened at thick films. Effects of surface roughness on cavitation or pressure distribution was depressed or even disappeared with increase of liquid film thickness. In case of upstream pumping seal, the circumferential width of cavitation was larger than that of downstream pumping seal, the width for middle grooving seal was larger than that of inner grooving seal, as well as the width enlargement with increase of inner dam reached to maximum when the radial width of inner dam was equal to that of outer dam. However, in case of downstream pumping seal, the width of middle grooving seal was smaller and decreased with increase of the inner dam. Effects of grooving position on cavitation were closely related to the function of spiral groove. Cavitation shranked at lower cavitation pressure but promoted at higher cavitation pressure. High cavitation pressure was beneficial to improving load-carrying capacity of the liquid film.