用于在双流体流动中施加物理边界的扩散界面混合方法
Diffuse-Interface Blended Method for Imposing Physical Boundaries in Two-Fluid Flows
AI总结：
本文提出一种扩散界面混合方法，通过混合双流体与不可变形固体的守恒方程在结构化网格上施加物理边界，并验证其在小界面宽度下可达到贴体网格3%以内的精度。
摘要：
多相流常见于蒸馏塔、鼓泡塔、流化床和换热器等化学工程过程。在多相流数值模拟中，计算域的物理边界通常由贴体非结构化网格定义；根据物理系统的复杂程度，这会导致耗时的网格生成，并且往往需要用户干预。此外，所生成的贴体非结构化网格可能包含大量倾斜单元，这对数值稳定性和精度是不利的。扩散界面方法允许使用简单的结构化网格，同时仍能捕捉所需的物理（例如固-流）边界。在本工作中，针对不可压缩双流体多相流模型，开发了一种用于施加物理边界的新型扩散界面方法。该模型适用于在化学工程过程中普遍存在的分散多相流，因为这种流态会在相之间产生高水平的质量和能量传递。扩散界面被用于定义物理边界，并且通过将双流体模型的守恒方程与不可变形固体的守恒方程相混合来施加边界条件。针对不同的界面函数和宽度，将扩散界面方法的结果与贴体非结构化网格的结果进行了比较。对于较小的界面宽度，流动剖面的精度不受界面函数选择的影响，并且相分数分布和流动行为与贴体网格所得结果相比在3%以内。随着界面宽度增加，扩散界面解在局部气体分数和总体气体持留率方面均偏离贴体网格解，导致差异最高达30%。
英文摘要：
Multiphase flows are commonly found in chemical engineering processes such as distillation columns, bubble columns, fluidized beds and heat exchangers. The physical boundaries of domains in numerical simulations of multiphase flows are generally defined by a conformal unstructured mesh which, depending on the complexity of the physical system, results in time-consuming mesh generation which frequently requires user-intervention. Furthermore, the resulting conformal unstructured mesh could potentially contain a large number of skewed elements, which is undesirable for numerical stability and accuracy. The diffuse-interface approach allows for the use of a simple structured meshes to be used while still capturing the desired physical (e.g., solid-fluid) boundaries. In this work, a novel diffuse-interface method for the imposition of physical boundaries is developed for the incompressible two-fluid multiphase flow model. This model is appropriate for dispersed multiphase flows which are pervasive in chemical engineering processes, in that this flow regime results in high levels of mass and energy transfer between phases. A diffuse interface is used to define the physical boundaries and boundary conditions are imposed by blending the conservation equations from the two-fluid model with that of the nondeformable solid. The results from the diffuse-interface method are compared with results from a conformal unstructured mesh for different interface functions and widths. For small interface widths, the accuracy of the flow profile is unaffected by the choice of interface function and the phase fraction distribution and flow behavior are within 3% compared to those from a conformal mesh. As the interface width increases, the diffuse-interface solution deviates from the conformal mesh solution in both the localized gas fraction and the overall gas hold-up, resulting in a difference up to 30%.
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