超低比转数自平衡多级离心泵转子模态分析

Modal analysis of super low-specific-speed self-balancing multistage centrifugal pump rotor

为了掌握多级离心泵转子振动特性,避免泵运行中发生共振,保证水泵运行的稳定性,基于软件ANSYSWorkbench对超低比转数自平衡多级离心泵转子进行模态分析.计算对比干态无流场预应力、干态有流场预应力及湿态有流场预应力3种情况下泵转子各阶次的固有频率,并提取泵转子的前8阶模态对应振型进行分析.结果表明:3种情况下,转子各阶反进动固有频率均小于同一阶次下的正进动频率;干态有流场预应力相比无流场预应力情况下各阶固有频率略有提高,说明流场预应力对泵转子起到一定的应力刚化作用;湿态下水对转子的质量力、黏性以及阻尼的影响会显著降低了泵转子各个阶次的固有频率,湿态下水的附加力对转子的模态影响更为明显;对比转子的前4阶振型,发现3种情况下转子各阶次的振动形式和最大振幅出现位置基本相同,其中第三阶为绕轴心的扭转振动,其余3阶振型对应为不同方向和不同形式的弯曲振动.

To grasp vibration characteristics of multi-stage centrifugal pump rotor and avoid occurrence of resonance during pump operation so as to guarantee the stability of operation,modal analysis on the rotor of a super low-specific-speed and self-balancing multistage centrifugal pump was carried out based on the commercial software ANSYS Workbench in this article.Natural frequencies under three conditions namely dry rotor without flow field pre-stress,dry rotor with flow field pre-stress and wet rotor with flow field pre-stress were calculated and compared.Further,the first eight modals of the rotor were extracted and analyzed.It is shown that the natural frequency of reverse precession is lower than that of forward precession for the same order.The natural frequency increases slightly under condition with flow field pre-stress compared with that without pre-stress,indicating that the flow field pre-stress can rigidize the pump rotor in a certain degree.Under wet condition,additional mass,viscous and damping effects of water have intensively decreased influence on the natural frequency,and the mass force of water has a more significant effect on the frequency.By comparing the first four order vibration modes of the pump rotor,it is found that vibration mode and position where the maximum vibration amplitude appears are identical basically under three conditions.The third order vibration is rotational vibration around the pump shaft-axis,while the other three vibrations correspond to bending vibrations with dif-ferent directions and shapes.