以某核电站汽轮机主调阀为研究对象,通过瞬态数值模拟计算,研究在小开度状态下主调阀关键部位的低频脉动机理。分析当阀门压比从较大值逐渐降低时阀腔内气流流动结构变化以及阀芯和管道处压力波动脉动频谱特性。结果表明,阀门小开度大压比工况下,蒸汽为附壁流动,壁面气流脉动幅值极低。当压比减小到接近临界分离压比附近,流场仍为附壁流动状态,但蒸汽射流开始出现交替性膨胀压缩的特征。当压比降低到临界分离压比以下时,蒸汽射流呈现出一侧分离,另一侧附壁的流动状态,且两侧射流均在附壁和分离状态之间不断交替,这种流动状态极其不稳定。当压比继续降低到一定程度后,气流经过阀芯喉部后可以形成相对稳定的分离射流状态。

In order to understand the mechanism behind the significant flutter of the main governing valve of a turbine in a nuclear power plant at small openings, transient numerical simulations were conducted. The variations in flow structure within the valve cavity and the pressure fluctuation spectral characteristics at the valve core and pipeline were analyzed as the pressure ratio decreased gradually at small openings. The results indicate that under conditions of small valve openings and high pressure ratio, steam exhibits attached-wall flow, with extremely low amplitude of wall airflow fluctuations. The maximum amplitude of airflow fluctuations at the valve core and pipeline walls is less than 100N. Through investigations at various openings, it was found that when the pressure ratio decreases to below a critical separation pressure ratio, the steam jet exhibits a separated flow on one side and attached-wall flow on the other side. Moreover, the flow on both sides of the jet alternates continuously between attached-wall and separated states, leading to extremely unstable flow conditions. The airflow fluctuation force at the valve core exists in a wide-frequency fluctuation range with amplitudes up to 2500N at Strouhal numbers ranging from 0.6 to 0.8, while the airflow fluctuation force in the pipeline exists in a wide-frequency range of 400 to 600Hz with amplitudes reaching 9000N. As the pressure ratio continues to decrease to a certain extent, the airflow passing through the valve core throat can form a relatively stable separated jet state. Compared to the critical separation state, the maximum amplitude of airflow fluctuation force at the valve core is only about 30%, while the pipeline airflow fluctuation force transitions from a wide-frequency to a single-frequency pattern, rapidly increasing to approximately twice the previous amplitude.

国家科技重大专项（HT-J2019-II-0010-0030）（HT-Y2019-Ⅰ-0002-0003）