超临界二氧化碳涡轮升速过渡中密封-转子系统的动力学行为

Dynamic behavior of seal-rotor system in a supercritical carbon dioxide turbine during acceleration transition

超临界二氧化碳涡轮密封的气动特性与转子运动存在强耦合关系。在变转速运行时,密封-转子系统的动力学特性会发生不确定的变化。基于动力学方程建立密封-转子非线性涡动模型的用户自定义函数,实现密封流场仿真与转子动力学的同步耦合分析,得到转子升速过程中密封的气动特性和转子运动特征,揭示升速时密封-转子系统的动力学特性演变规律。研究结果表明:自转速度增加使转子涡动中心在进动方向发生横向偏移,涡动半径逐渐扩大。转子涡动中心先下沉后抬升。升转速过程中密封动力系数具有显著的波动,高频范围内刚度的绝对值较大,阻尼的绝对值较小,有效阻尼具有较大的波动,密封稳定性降低。低转速运行区间,直接刚度和交叉刚度具有显著的高频波幅。高转速区间,直接阻尼具有显著的低频波幅。转速升高使有效阻尼的波动逐渐向高频迁移。在200 Hz附近,有效阻尼具有较高的幅值和集中分布。

There is a strong coupling relationship between the seal aerodynamic characteristics and rotor motion of su⁃percritical carbon dioxide turbine.The dynamic characteristics of the seal-rotor system undergo uncertain changes in rotor acceleration transition.The user-defined function of the seal-rotor nonlinear whirling model was established based on dynamic equations,which enables the synchronous coupling analysis of seal flow field simulation and rotor dynam⁃ics.The seal aerodynamic characteristics and the rotor motion characteristics during the rotor acceleration transition were obtained,and the evolution law of the dynamic characteristics of the seal-rotor system was revealed.The results show that,with the increasing of rotation speed,the rotor whirling center moves laterally in the precession direction,and the whirling radius increases gradually.The rotor whirling center sinks first and then rises.The seal dynamic coef⁃ficients fluctuate significantly in the process of rotor acceleration transition.The absolute value of stiffness is large in the high-frequency range,and the absolute value of damping is small.The effective damping has a large fluctuation,and the seal stability is reduced.In the low-speed operation range,the direct stiffness and cross stiffness have signifi⁃cant high-frequency amplitude.In high-speed range,the direct damping has prominent low-frequency amplitude.The increasing of rotation speed makes the fluctuation of effective damping gradually migrate to high frequency.The effec⁃tive damping has higher amplitude and concentrated distribution around 200 Hz.