基于局部流场修正的空化湍流场建模及相互作用机理研究

The unstable flow produced by cavitation in the blade-type hydraulic machinery seriously affects the safety, stability and efficient operation of the device. The purpose of this project is to explore the mechanism of the interaction between the unsteady turbulent flow field and cavitation, and to construct the appropriate model and method for numerical analysis of cavitation turbulent flow in the blade-type hydraulic machinery. A modified function based on the characteristics of local flow field would be introduced to study and ensure the large eddy simulation method considering the rotation constraint on the sub-grid stress model. Based on the theory of two-phase flow with multi-components and Henry's law, the real time effect of precipitation and dissolution of the non-condensable gas in the liquid phase would be analyzed. Meanwhile, compared the time scale of macroscopic cavitation phase change speed to the mean time scale of local turbulence fluctuation, the updated parameters of cavitation model based on local turbulent flow characteristic would be established. Referencing the idea of turbulent eddy viscosity modeling, a modified critical pressure stress cavitation model based on local flow characteristics would be proposed. On this foundation, the numerical simulation, cavitation image observation, the measurement of pressure pulsation and multi-point velocity fluctuation near the blade surface would be carried out in the simplified axial-flow pump model for water-jet propulsion. Furthermore, the DMD/POD method would be used to extract typical flow structures in cavitation flow field, and the characteristics and interconnection of cavity structure, turbulent vortex structure and pulsating signal would also be assurance, so as to provide theoretical support for modeling and analysis of cavitation turbulent flow in hydraulic machinery.

叶片式水力机械空化产生的不稳定流动严重影响设备的安全、稳定和高效运行。本项目旨在探索非稳定湍流场与空穴相互作用的机理，并构建适合于叶片式水力机械内空化湍流场数值分析的模型和方法。拟引入基于局部流场特征定义的修正函数，研究确定考虑旋转约束的亚格子应力模型的大涡模拟方法；根据多组分两相流理论和亨利定律，分析液相中不可凝结气体实时的析出和溶解的影响；将反映宏观空化相变速率的时间尺度与当地湍流脉动平均时间尺度比拟，以建立基于当地湍流场特征调制的空化模型参数；拟借鉴湍流涡粘建模思想，研究建立基于局部流场特征修正临界压应力的空化模型；在此基础上，以喷水推进轴流泵模型为具体研究对象，开展数值模拟、空化图谱观测、压力脉动和近叶片表面多点脉动速度测量；采用DMD/POD方法提取空化流场中典型的流动结构，把握空穴结构、湍流涡结构和脉动信号的特征和关联，从而为水力机械内的空化湍流场建模和分析提供理论支撑。

项目围绕叶片式水力机械内空化、空蚀、湍流的共性问题，采用理论分析、数值建模和实验测试相结合方法开展研究工作。探索了系统旋转对湍动能输运、边界层稳定性的影响，通过引入扩展内禀平均旋转张量，提出了合理的考虑旋转效应修正的建模方法；为考察湍流场对空化相变速率和临界压力的影响，通过与湍流建模方法进行比拟，引入局部流场信息的物理量（剪切应变率），提出了优化空化模型的方法，并成功应用于捕捉水翼多模态空化演化现象，发现了凝聚激波和回射流耦合交替出现现象；通过对云空化溃灭过程机制的分析，从能量输运的角度出发，构建了空蚀风险预估的模型和数值计算方法，针对水翼表面空蚀风险预估结果与表面油漆破坏实验一致；在传统人工智能神经网络的基础上，通过引入考虑物理机制约束的控制方程，提出了基于物理约束的机器学习和数据融合的统一框架，成功应用于方程求解、数据修复、高雷诺数湍流场求解等；设计了适用于水力机械的旋转叶片表面压力脉动同步采集实验装置，并首次成功应用于喷水推进泵旋转叶片表面压力脉动测试。.相关研究可为空化湍流场数值分析提供模型和数值分析手段，为叶片式水力机械的空化性能预测和叶片表面空蚀风险评估提供支撑，为旋转叶片表面压力脉动测量提供了可行的方案和技术路线。还可为水下航行体推进器、超空泡阻、两栖车喷水推进、弹体的发射和入水等性能分析、空化空蚀影响及风险评估提供技术支撑。.