倾斜椭圆微孔端面机械密封的回吸现象及对泄漏量影响

中文摘要: 目前研究成果直接或者间接表明机械密封端面加工孔或槽可能会产生间隙流体的回吸，从而减少泄漏量，回吸的现象和机理都需要深入研究。基于Fluent多相流空化模型，针对倾斜椭圆形微孔端面机械密封，建立了其中1个微孔周期的间隙流体的3维数值计算模型，通过改变内外径压差、转速等密封工况参数，研究了回吸现象产生的原因以及回吸现象对泄漏量的影响。首先，通过流动因子判定流动状态、网格关性分析确定网格尺寸，并于文献计算结果对照，保证了计算模型的正确性。然后，通过数值模拟实验，在靠近泄漏侧微孔单元的 r-θ平面流线图和密封间隙出口截面径向速度云图中直接观察到了回吸现象。随后，分析了 r-θ平面的压力场、径向方向速度场，结果表明，由于微孔而存在发散间隙，因为动压效应引起出口附近的流体压力降低，低于密封间隙出口压力，造成了间隙流体产生回吸现象。回吸现象因流体动压效应的增强而增强，压力的降低将导致空化现象，空化效应阻止了回吸的增强。最后，通过分析外泄量和回吸量曲线，研究了回吸现象在不同内外径压差Δ p和转速 n下的变化规律。随着回吸现象的出现，泄漏量会出现明显的降低，甚至会出现零泄漏。可以利用倾斜微孔的回吸现象降低机械密封的泄漏量。
Abstract:It has been showed directly or indirectly that the lubricant is possible to be sucked back into the mechanical seal with dimples or grooves in the existing studies.This phenomenon,termed "outlet suctio" in this paper,may decrease the leakage.Further studies are still required for this phenomenon and its mechanism.A three-dimensional fluid numerical simulation,based on the multiphase flow cavitation model in Fluent,was developed for the mechanical seal with inclined elliptical dimples.The causes of outlet suction and the influence of the outlet suction on leakage were studied by changing the differential pressure between the inner and outer diameter and the rotation rate.Firstly,in order to ensure the accuracy of calculation model,the fluid factor was calculated for the flow pattern check,the grid independence was tested for the grid size,and the simulation result was compared with the reference.Secondly,in the numerical simulation experiments,the phenomenon of outlet suction was observed directly in the streamline plots on the r-θ section of calculation unit beside the outlet section and the velocity distribution contours in radial direction on the outlet section.Thirdly,the pressure and radial velocity distribution on r-θ section was discussed.The results showed that the outlet suction occurs because the pressure close to the seal outlet falls below the external atmospheric pressure.This pressure decrease is caused by the hydrodynamic effect near the divergence gaps of dimples.The increase of hydrodynamic effect enhances the outlet suction.When the decreased pressure reaches the cavitation pressure,the cavitation occurs.The cavitation effect hinders the increase of outlet suction.Finally,the effect of Δ p and n on outlet suction,and the effect of outlet suction on the leakage decrease were studied based on the analysis of the out flow rates and outlet suction flow rates.The leakage decreases because of the outlet suction,even to zero.The outlet suction caused by inclined elliptical dimples can be employed to decrease the