泵用不可压缩流体密封刚度系数分析

Analysis of the stiffness of the incompressible seal in pump

针对不可压缩流体密封弹性支承的问题,分析了负刚度产生的原因。选用三维流动模型,数值求解Navier-Stokes方程。采用k-ε湍流模型,计算LNG泵的节流衬套和口环密封的动力特性系数,分析在LNG泵不同转速工况下,不可压缩流体密封的动特性变化,并与2倍间隙密封的动特性相比较。模拟了密封腔内部流场,通过分析比较密封圆周上压力和速度分布,研究等截面环形产生负直接刚度的原因和影响因素。研究结果表明:等截面环形密封和槽道式密封的1倍间隙直接刚度小于2倍间隙,1倍间隙交叉刚度大于2倍间隙,密封磨损后稳定性反而提高;转速升高使等截面环形密封和槽道式密封的直接刚度下降,交叉刚度增大,造成稳定性下降;等截面环形小间隙密封,在高转速工况下容易产生负直接刚度,影响转子的稳定性,工程上建议采用槽道式密封控制不可压缩流体泄漏。

To investigate the flexible support of the incompressible seal , negative stiffness characteristic was ana-lyzed .The rotor dynamic coefficients in the neck bush and the ring seal in the LNG pump were predicted by emplo-ying three-dimensional flow model , theκ-εturbulence model and numerically solving the Navier-Stokes equations . The dynamic characteristics were compared in the incompressible seals over a range of rotating speeds and between nominal clearance and twice clearance seals .Through simulating the incompressible flow , as well as analyzing and comparing the circumferential distributions of the pressure and velocity , the reasons for the negative direct stiffness in the uniform annular seal were discovered and the influences on the negative direct stiffness were also found .The results show that：for both the annular seal and the grooved seal, the direct stiffness of twice clearance seal was higher than that of the normal clearance seal , but the cross stiffness of twice clearance seal was smaller than that of the normal clearance seal .It indicated the rotor stability was improved after seal wore .The direct stiffness dropped and the cross stiffness increased with the increase of the rotating speed , which caused rotor stability reduction .In the high rotating speed condition , the annular seal with a small clearance was vulnerable to perform a characteristic of negative stiffness , which destroyed the stability of the rotor system .It is recommended that the grooved seals are applied to the pump to control the incompressible flow against leakage instead of the annular seal .