CFD模拟的高阶曲线混合网格生成
High-order curvilinear hybrid mesh generation for CFD simulations
摘要：
本文介绍了一种适用于高雷诺数流动模拟的高阶混合网格生成的半结构化方法。这是通过在壁面附近的粘性边界层中使用高度拉伸的单元来实现的。CADfix用于首先修复CAD几何结构中的任何可能缺陷，然后生成基于中间对象的域分解，该域用适合于生成棱柱体或六面体单元的分区包裹壁边界。后者是一个新的显着特点的方法，允许获得良好形状的六面体网格在边界层的角落或交界处。中间对象方法允许对边界层网格的“厚度”进行比通常使用推进层技术可实现的更大的控制。CADfix随后在近场区域生成棱柱体和六面体单元的混合直边网格，模拟边界层，在远场区域生成四面体单元，覆盖域的其余部分。在近场区域的网格提供了一个框架，有利于生成，通过等参数技术，层的高度拉伸的元素与点的分布在垂直于定制的壁的方向，以有效地和准确地捕捉在边界层中的流。最后一步是使用Nektar++框架中的高阶网格生成器NekMesh生成高阶网格。NekMesh使用CADfix API作为几何引擎，处理高阶网格生成过程中所需的CAD几何的所有几何查询。为了说明的目的，我们将用一个简单的几何形状，即NACA翼尖，详细地描述这种方法。最后，我们将提出两个应用程序的例子，以合理复杂的几何形状提出的美国宇航局作为计算流体动力学验证的情况。
英文摘要：
We describe a semi-structured method for the generation of high-order hybrid meshes suited for the simulation of high Reynolds number flows. This is achieved through the use of highly stretched elements in the viscous boundary layers near the wall surfaces. CADfix is used to first repair any possible defects in the CAD geometry and then generate a medial object based decomposition of the domain that wraps the wall boundaries with partitions suitable for the generation of either prismatic or hexahedral elements. The latter is a novel distinctive feature of the method that permits to obtain well-shaped hexahedral meshes at corners or junctions in the boundary layer. The medial object approach allows greater control on the "thickness" of the boundary-layer mesh than is generally achievable with advancing layer techniques. CADfix subsequently generates a hybrid straight sided mesh of prismatic and hexahedral elements in the near-field region modelling the boundary layer, and tetrahedral elements in the far-field region covering the rest of the domain. The mesh in the near-field region provides a framework that facilitates the generation, via an isoparametric technique, of layers of highly stretched elements with a distribution of points in the direction normal to the wall tailored to efficiently and accurately capture the flow in the boundary layer. The final step is the generation of a high-order mesh using NekMesh, a high-order mesh generator within the Nektar++ framework. NekMesh uses the CADfix API as a geometry engine that handles all the geometrical queries to the CAD geometry required during the high-order mesh generation process. We will describe in some detail the methodology using a simple geometry, a NACA wing tip, for illustrative purposes. Finally, we will present two examples of application to reasonably complex geometries proposed by NASA as CFD validation cases.
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