高温高压热力学效应对非定常空化流动的影响机制研究

Cavitation is one key issue that constricts the equipment performance, safe and stable operation for the hydraulic machineries, such as nuclear main pump, which operate under high temperature and pressure conditions. The thermodynamic effect for cavitation is obvious under those conditions, and it is essential to reveal the mechanism of thermodynamic effect in order to accurately predict the cavitation performance for high-temperature and high-pressure hydraulic machineries. In this study, the mechanisms of thermodynamic effect on cavitation flow are focused, and experiments on unsteady cavitation flow around a hydrofoil are performed under high temperature and pressure conditions. The main contents are as follows: First, in our experimental facility designed for cavitation flow with high temperature and pressure, the growth, development, shedding and collapse of unsteady cavitation bubble are captured using high-speed photography, and then the morphological features and evolution laws for unsteady cavitation are analyzed. Then, PIV experiments are conducted to obtain the key information of cavitation flow field, such as the vorticity distribution. The structures and evolution features of cavitation flow field are studied to reveal the correlated characteristics between the unsteady cavitation and vorticity evolution. Based on the results of visualization experiment, combined with theoretical analyses such as bubble dynamic, the coupling transport regularities between mass transfer and energy transfer process are analyzed, the mass transport equation that includes the thermodynamic effect are developed, and the influence mechanisms of thermodynamic effect on unsteady cavitation are revealed. The results can provide theoretical basis and technical support for hydrodynamic design, safe and stable operation for hydraulic machinery under high temperature and pressure.

空化是制约核主泵等高温高压水力机械性能提升和安全稳定运行的瓶颈。在高温高压条件下，空化伴随着明显的热力学效应，揭示其作用机理对准确预测该类水力机械空化性能至关重要。本项目以阐明热力学效应对空化流动的影响机制为目标，开展高温高压条件下绕水翼非定常空化流动的实验研究，主要内容有：在研制的高温高压空化流动实验装置上，利用高速摄影技术，捕捉非定常空化的生长、发展、脱落及溃灭过程，掌握高温高压非定常空化演化的形态与规律；进而利用PIV技术，获取高温高压空化流场涡量分布等关键信息，阐明空化流场结构特征与演化规律，揭示非定常空化与旋涡的关联特性；在上述实验结果基础上，结合空泡动力学等理论，分析空化流动中质量传输与能量传输的耦合规律，建立包含热力学效应的质量输运方程，揭示高温高压热力学效应对非定常空化流动的影响。研究成果为我国高温高压水力机械的水动力学设计及安全稳定运行提供理论基础与技术支撑。

在水力机械、核能动力、航空航天等诸多领域，流体空化问题是制约系统性能提升的关键因素之一。特别是，在高温高压条件下，空化过程中伴随不容忽视的热力学效应，其对非定常空化流动的影响机制亟待揭示。本项目以多相流体及汽泡动力学理论为基础，采用数值模拟及可视化试验方法，从空化形态演变特性、云空化脱落机制、空化场参数分布规律等角度出发，对多种温度、压力、空化诱发结构条件下水体的空化流动特性展开研究。.首先，针对常温水体空化，发展了一种同时考虑表面张力、二阶空泡运动项及非凝结气体的非线性空化模型，获取了绕水翼非定常空化流动特征，分析了压力脉动特性及回射流机制，得到了三维水翼表面云状空泡随时间的形态演化规律，并结合涡量输运方程，阐明了非定常空化与旋涡的相互作用机制。其次，提出了一个考虑热效应的ZGB空化修正模型，建立了适于高温流体空化流动数值计算方法，开展了高温流体绕水翼空化流动特性研究，获取了温度、压力、汽相体积分数、湍动能等流动特征参数的分布规律，描述了无量纲流动参数、无量纲空化尺度参数及热力学参数的关联特性，分析了空化热效应的影响因素及其强度变化规律，阐明了空化流动中质量传输与能量传输的耦合规律。与此同时，研制了一套高温高压多相流体流动可视化测试平台，开发了流场高频脉动参数及瞬时图像同步采集系统，并以文丘里管为空化诱发结构，开展了多种工况条件下文丘里管空化可视化试验，获取了不同温度、压力下的空化形态特征。.研究工作有助于揭示热效应对非定常空化流动的影响机制，加深对高温高压流体空化机理的认识，相关成果可为高温高压多相流体流动系统（特别是高温高压水力机械内部流动）的设计与优化提供一定的理论基础和技术支撑。