分形裂缝中空化泡溃灭机理及其空化清洗效应研究

The underwater fractures which are the potential risks of the hydraulic structures must be cleaned before repaired. The cavitation cleaning is one of the important physical methods which can deep into the fractures and clean the inner walls effectively. However, the fractures have complex fractal features. The weak study of the interaction mechanism between the cavitation bubble and the fractal fracture can’t meet the demand of engineering well. This project focuses on the principles of the cavitation cleaning in fractal fracture for higher efficiency. Firstly, the lattice Boltzmann method, which is based on mesoscopic kinetics, is introduced innovatively in the project. Due to the advantages in the respect of multiphase and complex boundary modeling, it will be valid and efficient to model the vapor-liquid-solid multiphase fluids. Secondly, the constructing approach of fracture sample with controllable geometry features is proposed for the consistency between numerical model and the corresponding experimental sample. So the purpose of the experiments is to verify the numerical models. Finally, a series of simulations will be developed to investigate the quantitative relationship between collapsing cavitation bubble and fractal wall base on a series of fractal parameters. The achievements on two levels are expected. For microcosmic level, the microcosmic mechanism of interaction between collapsing cavitation bubble and fractal feature can be revealed. For microscopic level, the interaction mechanism and the cleaning effects between the fractal fracture and the collapsing cavitation bubble with shock wave and jets. As a result, it is expected that a set of experiment and analysis system on cleaning the fractal fracture to establish the theoretical foundation and the technical support for cleaning the underwater fracture effectively, and to expand the method to investigate the interaction between cavitation bubble and arbitrary complex geometry boundary.

影响水工建筑物安全的水下裂缝在修补前要进行必要的清洗，能够深入裂缝的空化清洗是一种高效的物理手段。然而，混凝土裂缝具有复杂的分形几何特征，现有空化泡与固壁间的相互作用研究尚无法满足工程诉求。项目以空化泡溃灭与具有分形特征的裂缝壁面间的相互作用为对象开展研究。首先，创新性地引入基于介观视角的格子Boltzmann方法，利用其多相流、复杂几何边界数值建模优势，构建高效的汽-液-固多相耦合数值模型；其次，提出几何特征可控的实体裂缝模型构造方法，构建与数值模型几何特征一致的实验模型，以通过实验验证数值模型的有效性；最后，通过开展系列数值实验，以分形几何参数为桥梁建立空化泡溃灭各物理量时空演化与分形裂缝几何特征之间的量化关系。项目拟从微观、宏观两个层面揭示分形裂缝与空化泡相互作用的机理及其空化清洗效应，为实现水下裂缝高效清洗奠定理论和技术基础，也为研究空化泡与任意复杂几何边界相互作用探索有效路径。

分形裂缝空化清洗问题本质上是汽-液-固多相耦合问题，可以进一步推广为空化泡和任意复杂几何固壁相互作用的问题。然而，由于涉及复杂几何边界，使得空化泡溃灭难以建模、演化过程难以量化、实验验证难以实施。本项目从数值建模入手，引入介观的格子Boltzmann方法，利用伪势模型并耦合改进的作用力格式和不同状态方程，发展了空化泡近壁溃灭的格子Boltzmann模型及其热格子模型。在基础模型基础上建立并验证了平直固壁、规则几何固壁、曲面固壁、任意复杂几何固壁、润湿性可调固壁、温度可调固壁等多种固壁附近空化泡溃灭的数值模型，并开展系列性数值实验，提出了用形态学分析量化描述空化泡近壁溃灭的方法，研究空化泡溃灭近壁溃灭机理及空化效应。基于超高速摄像机系统和高电压水下致泡装置建立了空化泡近壁溃灭实验平台，并开展了空化泡溃灭与单/双平直固壁、曲面固壁、超疏水固壁、复杂几何固壁、分形裂缝等的相互作用实验。本项目的研究提高了空化泡近壁溃灭模型的效率，探索了空化泡近壁溃灭演化过程量化描述手段，实现了数值模型和实验结果的相互验证，为研究空化泡近复杂几何及不同属性固壁溃灭问题提供了可行且有效的途径，在流体力学仿真软件领域也有潜在的应用前景。