迷宫密封非线性动力特性的数值计算方法

Numerical calculation of nonlinear dynamic characteristics for labyrinth seals

随着旋转机械的高参数化,迷宫密封气流激振问题越来越严重.为了能够深入分析迷宫密封与转子耦合系统的非线性动力学行为,提出了一种基于商用CFD软件Fluent计算的数值方法.通过流场分析计算出不同偏心和不同涡动角速度下的迷宫密封非线性气动力,进而求出相应的动力特性系数,从而得到任意位移和速度扰动下的密封非线性气动力.同时讨论了Fluent中入口总压和静压的设置.数值计算表明,气动力与偏心的关系是非线性的,正向预旋不利于系统的稳定性;在有预旋的情况下,随着进出口压差增大,交叉刚度负向增大,主阻尼减小,易使转子系统失稳.

With the development of rotating machinery towards higher speed and higher efficiency, the vibration excited by fluid in labyrinth Seal occurs more frequently. In order to reveal the nonlinear dynamic behaviour of rotor-seal system, a numerical method to calculate the nonlinear fluid exciting forces was put forward based on the commercial computational fluid dynamics （CFD） software Fluent. The nonlinear aerodynamic force was calculated with various eccentricities and whirl speeds, and under each eccentricity and whirl speed, the dynamic coefficients of labyrinth seal were also calculated. The nonlinear aerodynamic forces of the seal under any displacement and velocity disturbance were obtained. It was discussed how to set the total and static inlet pressure by Fluent. The calculation results indicated that there was nonlinear relationship between aerodynamic forces and eccentricities, and positive pre-swirling had negative effect on the system stability. On condition of pre-swirling speed at the seal inlet, when increasing the pressure difference, the cross stiffness was increased in the negative direction, and the direct damping was decreased, which could lead to instability of rotor system.