船舶蒸汽蓄热器放汽管路热冲击特性预测

船舶放汽管路具有放汽周期短、热冲击能量高、负荷波动大的特点,其运行特性直接影响蒸汽蓄热器的安全稳定工作。以典型船舶蒸汽蓄热器放汽管路为原型,采用标准k-ε模型计算湍流脉动过程,通过数值模拟的方法计算了船舶蒸汽蓄热器放汽管路的水动力特性,获得流速、压力、湍动能及壁面剪切应力等参数的分布规律,基于流致振动而诱发流体热冲击的机理,揭示了与流致振动密切相关的热冲击能量图谱。计算结果显示,在高温高压饱和蒸汽掺混流动过程中,三通管区域呈现蒸汽冲击流速高,湍流脉动剧烈,壁面剪切应力大的特点;基于蒸汽热冲击能量分布图谱,放汽管路上弯管和三通管件局部区域蒸汽热冲击能量较大,其中三通管热冲击能量最大,可以预测三通管件承受的热冲击破损最严重,实物检测破损数据验证了数值预测结果。

Prediction and investigation on thermal shock characteristics of discharging pipe for ship steam accumulator

The ship discharging pipe has characteristics of short discharging period, high thermal shock energy and large fluctuation load, which directly affect safe and steady operation of a steam accumulator. In this study, typical ship steam accumulator discharging pipe is taken as the prototype. Turbulent fluctuation is analyzed by using the standard k-ε equation. The hydrodynamic characteristics for ship steam accumulator discharging pipe are calculated by CFD simulation method. Velocity, pressure, turbulence kinetic energy and wall shear distributions are obtained. Based on the prediction mechanisms of thermal shock generated by flow induced vibration, shock energy pictures closely related to flow induced vibration are revealed. The calculated results show that during mixed flow of high temperature and pressure steam, high velocity, severe turbulence fluctuation and large wall shear occur around T-junction. Based on steam thermal shock energy pictures, thermal shock energy is higher at the elbow and T-junction, while the maximum shock energy occurs at the T-junction for discharging pipe. These calculated results predict that thermal shock damage for T-junction is more serious. The actual test data for T-junction demonstrate the numerical prediction results.