基于格子Boltzmann方法的水流掺气数值方法研究

针对掺气水流的物理模型气泡尺寸的精细测量难题和现有数值模拟方法尚难实现掺气水流气泡尺寸及其分布的准确模拟问题，本项目基于格子Boltzmann方法兼具微观本质和介观特点，算法简单，适合复杂边界条件，易于并行计算的突出功能，开发一套能够模拟高流速水流掺气过程的数学模型。该模型可以实现精确模拟气体从水气界面掺入形成气泡及其在流动水体中随流输运、紊动扩散、上浮、分裂、合并、溢出水气界面的动态全过程。模型经实验验证后，用来对比研究运动水体自由表面掺气和过流边界突变的强迫掺气过程中气泡大小及分布与气泡上浮速度、紊动特性的关系，实现掺气浓度场和流速场的精细耦合模拟。研究成果不仅为更深入探讨掺气减蚀机理提供一种新的研究手段，而且可为工程设计与优化提供科学依据，因此，具有重要的研究价值。

Aiming to the challenge of measuring accurately the bubble size distribution in aerated flow by physical model or simulating it by existing numerical methods, a mathematical model basing on lattice Boltzmann method is proposed to simulate the air entrainment process in high-velocity flow. The proposed method has intrinsic microscopic and mesoscopic characteristics, so its algorithm is simple, easy to implement, suitable for complex boundary conditions, easy to parallel computing. The proposed model can simulate accurately the dynamic process of the gas bubbles formation from the water-air interface and its evolution which includes transport with flow, turbulent diffusion, floating, splitting, merging, and spilling. Validated by experiments, the proposed model is used to study comparatively the relationship between bubbles floating velocity, turbulence characteristics and bubble size distribution during air entrainment process which includes free surface air entrainment process and forced air entrainment process caused by mutative boundaries. Meanwhile, air concentration field and velocity field can be obtained simultaneously by detailed coupling simulation. This study not only provides a new tool for investigating aeration mechanism, but also can provide scientific basis for engineering design and optimization. Therefore, this study has important research value.