一种满足复杂边界条件的多相流扩散界面IBM研究及其应用

Two-phase fluid flow over complex/moving boundaries is ubiquitous in nature and industrial applications. Diffuse interface Immersed Boundary Method (IBM) is an efficient numerical method to simulate complex/moving boundary problems. However, it is commonly used for single phase fluid flow and only considers the Dirichlet boundary condition. To overcome this challenge, this project aims to develop a multiphase-diffuse interface IBM that can accurately implement both the Neumann and the Dirichlet boundary conditions, and to effectively simulate two-phase fluid flow over complex/moving boundaries. The project includes: Mainly focus on development of an IBM for complex/moving objects, which is able to accurately implement the two types of boundary conditions; Effectively combine the developed IBM and the hybrid-phase field-LBM (Lattice Boltzmann Method, LBM) to account for the problems with large density/viscosity contrast; Incorporate the Adaptive Mesh Refinement (AMR) technique into the developed multiphase-diffuse interface IBM to efficiently capture the free fluid interface as well as the flow field near the solid boundaries; Validate the developed methods by simulation of the dynamic wetting on a curved surface, the water entry problems and so forth. This project is innovative in the field of diffuse interface IBM and simulation of complex multiphase flow problems. It helps to establish a numerical framework for diffuse interface IBM to implement both the Neumann and the Dirichlet boundary conditions. Additionally, through a direct numerical simulation by the developed methods, it also helps to investigate the detailed physical mechanism of the interactions between the two-phase fluid flow and complex/moving boundaries.

含复杂边界/动边界的两相流绕流是众多自然现象和工业应用中共有的前沿基础科学问题。扩散界面IBM（浸入边界法）能高效模拟复杂边界/动边界绕流，但现有方法多用于单相流绕流且仅考虑Dirichlet边界条件。为此，本项目拟发展一种同时满足Neumann和Dirichlet边界条件的多相流扩散界面IBM，高效且准确地模拟含复杂边界/动边界的两相流绕流问题。研究内容包括：着重发展一种适用于复杂边界/动边界且精确满足各类边界条件的多相流扩散界面IBM；将该方法与混合有限差分-相场-LBM（格子玻尔兹曼方法）相结合实现大密度比/黏度比问题的稳定计算；引入网格自适应技术提高计算精度和效率；应用发展的方法模拟液滴撞击曲面、圆柱入水等问题验证其有效性。通过本项创新性研究，不仅能构建同时满足Neumann和Dirichlet边界条件的扩散界面IBM模型，还能探索揭示复杂多相流动的演化机理和物理规律。

含复杂边界以及运动边界的两相流绕流问题是众多自然现象和工业应用中共有的基础科学问题，扩散界面浸入边界法能有效模拟复杂边界及动边界绕流，本研究发展和完善了高效模拟含复杂边界及运动边界的多相流浸入边界格子玻尔兹曼方法，将多相流扩散界面浸入边界法与混合有限差分相场格子玻尔兹曼方法相结合；在多相流浸入边界-格子玻尔兹曼方法中引入交替模板网格自适应技术，精细且高效的计算含有复杂边界的多相耦合问题；将多相流扩散界面浸入边界法与结构物运动方程相结合，考虑了含有运动边界的三相耦合问题；开展了含复杂边界的多相耦合问题如液滴撞击圆柱，液滴撞击曲面，结构物入水等问题的数值分析；本项目研究过程中还发展了能够考虑柔性运动边界的浸入边界格子玻尔兹曼方法，并对含有复杂运动边界的流固耦合问题如主动变形的仿鱼类游动问题以及被动变形的柔性板流固耦合问题开展了数值分析。