蒸汽浸没射流相界面微观结构动态演变与凝结压力振荡耦合机制研究

Steam jet condensation is a core technology in pressure relief system in nuclear reactor, it remains a perennial concern from last century. However, in the process of pressure relief, pressure oscillation phenomena occurs due to steam condensation, which may destroy the facility in the pressure relief system and have a negative impact on nuclear reactor. Although several researches have been conducted on condensation oscillation, there is lack of the mechanism knowledge and suitable eliminating methods for condensation oscillation. The dynamic characteristic of microstructure in the steam-water interface, such as development of interfacial wave and turbulent vortexes have great effect on the condensation oscillation characteristic and closely related to the mechanism of condensation oscillation. Therefore, in this program, the dynamic characteristic of interfacial wave and turbulent vortexes in the steam-water interface will be investigated through experimental, theoretical and numerical methods to release the condensation oscillation mechanism and to seek suitable method for eliminating condensation oscillation. Firstly, the dynamic characteristic of interfacial wave and turbulent vortexes will be investigated experimentally. Then the generation and development mechanism of interfacial wave and turbulent vortexes will be understand, and related models will be developed based on experimental results. Then the relationship between the dynamic characteristic of interfacial wave and turbulent vortexes and fluctuation character of steam-water macroscopic interface can be obtained. The condensation oscillation mechanism can be released. Based on the mechanism model, the condensation oscillation intensity, dominant frequency and propagation characteristic of dynamic pressure wave can be predicted theoretically. Finally, based on the heat transfer model and interface transport model developed with interfacial wave and turbulent vortexes model, the dynamic process of steam jet condensation can be simulated. Then detailed information at steam-water interface of condensation oscillation can be simulated.

蒸汽浸没射流凝结是核反应堆堆芯余热快速排放的关键技术，但射流凝结产生的压力振荡会对泄压设备造成破坏，影响反应堆安全。目前针对凝结压力振荡的宏观特性研究存在凝结振荡机理认识不统一，振荡模型不准确等问题。本文将对汽液相界面微观结构的动态演变特征和机制进行研究，获取相界面微观结构动态演变与宏观结构凝结压力振荡耦合关系，探索凝结压力振荡的产生机理。首先采用实验方法对汽液相界面和混合层的微观瞬态结构特征、动态变化规律进行研究，获得射流界面波产生与传播理论模型以及混合层内湍流涡发展模型。进而研究在界面波和湍流涡影响下的汽液相界面整体动态变化规律，揭示凝结压力振荡产生机理，获得凝结压力振荡主频、强度及压力波传播的预测方法。最后开展蒸汽射流凝结动态数值模拟，耦合界面波和湍流涡相关模型，模拟获得射流凝结汽液相界面动态变化规律及压力振荡特性，进一步探索凝结压力振荡规律和产生机理。

高速蒸汽射流凝结过程具有高效的热质交换能力，广泛应用于电力、动力等领域。但目前对高速蒸汽射流凝结换热特性和压力振荡特性的研究主要以宏观为主，对于包含汽液热质交换界面的两相区域的微观流动与压力振荡及换热之间的关系尚不清楚。为此，本项目开展了蒸汽浸没射流相界面微观结构动态演变与凝结压力振荡耦合机制研究。首先，首次捕捉到高速蒸汽浸没射流内部汽液混合层的周期性演化过程和大尺度两相卷吸涡的演化规律，获得了混合层厚度和卷吸涡尺度沿流向的分布规律，建立了卷吸涡形成与脱落模型，并在此基础上得到了混合层特征厚度和卷吸涡特征尺度的半经验预测公式，预测值与实验值吻合良好。其次，针对混合层卷吸涡演化与蒸汽射流凝结压力振荡的关系开展了研究，揭示了蒸汽浸没射流凝结压力振荡的微观产生机制是由上下侧汽液混合层中卷吸涡的周期性演化和射流尾部周期性的涡团脱落造成。射流附近高频压力振荡是由混合层中卷吸涡的周期性演化和射流尾部周期性涡团脱落引起的射流高频横向振荡导致；射流附近低频压力振荡是由配对涡团周期性脱落引起的射流整体低频振荡导致；射流下游压力振荡是由周期性脱落涡团在下游的凝结振荡造成。结合卷吸涡脱落模型，提出了涡脱落无量纲特征主频的预测公式。进一步通过数值模拟研究发现射流膨胀压缩波会导致喷嘴出口相界面快速波动是引起射流流场压力振荡的主要原因。最后，针对汽液混合层的凝结换热特性开展了研究，建立了混合层的卷吸换热模型，发现混合层对周围过冷水的卷吸夹带通过间歇性演化的大尺度卷吸涡和混合层外表面持续产生的大量小尺度卷吸涡共同完成，提出了混合层单位体积换热量和平均凝结换热系数的预测公式，最后获得了混合层局部凝结换热系数随流向的分布规律。发现换热剧烈区域主要集中在界面凸起的汽团两相区和射流尾部的两相区域。