阻旋栅对密封静力与动力特性影响的数值分析与实验研究

Numerical and experimental research on performance of swirl brakes for the static and dynamic characteristics of seals

密封动力特性对旋转机械转子系统稳定性影响较大,在密封入口端部设置阻旋栅是提高密封稳定性的有效方法。设计加工了无/有阻旋栅共5种密封结构,从数值分析与实验研究两个方面研究阻旋栅对密封静力与动力特性的影响规律。建立阻旋栅密封静力特性CFD理论模型,数值分析阻旋栅对密封泄漏量、切向速度以及周向压力分布的影响;应用不平衡同频激励法实验研究阻旋栅对密封动力特性的影响。研究结果表明:阻旋栅可降低密封的泄漏量,减小密封内流体的切向速度,进而降低密封内流体的周向压力差,且随着阻旋栅周向稠度与径向长度的增加,这种作用逐渐增大,这是阻旋栅抑制气流激振力的主要原因;预旋是密封产生交叉刚度的重要因素,密封的交叉刚度随进出口压比与转速的增加而增大;阻旋栅可有效降低密封的交叉刚度,增加密封的主阻尼,提高密封的稳定性。本文研究揭示了阻旋栅抑制密封气流激振力的机理,为设计阻旋栅密封提供理论依据。

The seal dynamic characteristics play an important role in rotating machinery rotor system stability. The use of swirl brakes at the inlet of seals is an effective method to improve the seal stability. The paper designs five kinds of seals without and with swirl brakes. Numerical and experimental research on the performances of swirl brakes for the static and dynamic characteristics of seals are investigated. The paper sets up the swirl brake seal static characteristics CFD numerical model to analyze the performance of swirl brakes on seal leakage, the tangential velocity and pressure distribution. Experiments are presented to identify the dynamic characteristics coefficients using an improved impedance method based on un- balanced synchronous excitation method. The results show that compared to the traditional seals, the seals with brake seals have less leakage, lower fluid tangential velocity and smaller circumferential pressure difference. With the increase of swirl brake quantity in the circumferential direction and swirl brake radial length, this effect increases gradually. It is the main reason why swirl brakes reduce flow-induced force. Preswirl is a main factor for seal cross stiffness coefficients. The seal cross stiffness coefficients increase with inlet/outlet pressure ratio and rotational speed. The swirl brakes can effectively reduce the cross-couple stiffness and increase the direct damping for a variable conditions. It is believed that the results of this study will assist in improving the design of annular seal.