面向复杂流动和几何的各向异性混合网格的并行及自适应生成方法

Hybrid anisotropic mesh related methodologies are studied for flow simulations of advanced aerospace vehicle design, where semi-structured prisms and unstructured anisotropic tetrahedra are configured on the boundary layer and remaining region, respectively. Adaptive flowchart is introduced to analyse flow features with unknown geometry positions and shapes. Three key technologies are developed to address the fundamental issues involved in these methodologies. Firstly, a level set PDE based technique is employed for boundary layer mesh generation, and the solver is based on the boundary element method. Secondly, by combining the metric based mesh sizing tool and local mesh modification operations, a unified adaption approach is developed for both unstructured and boundary layer parts of the mesh. Surface adaption is allowed as well following the similar approach for the volume mesh. Finally, because any time-consuming sequential bottleneck is unacceptable in time critical and large scaled aerodynamics simulations, all the mesh generation approaches are parallelized so that the entire simulation pipeline can run on a distributed system. The final goal is to get a set of in-house CFD tools based on these anisotropic hybrid mesh related methodologies. These tools can handle the aerodynamics problems configured with very complex geometries in a highly automatic and fully parallel manner, where more than thousands of computers cores can be used to solve a simulation problem that contains hundreds of millions of freedoms. Benchmarks and industry examples for typical inflow and outflow problems are solved to validate and verify the developed methodologies and software tools, including those with moving boundaries.

面向飞行器设计中的复杂流动问题，研究如下网格生成方法：边界层采用各向异性三棱柱单元，内部布置各向异性四面体单元，引入自适应流程解析位置未知的各向异性流场。解决制约这类网格方法有效应用的关键问题。首先，基于水平集法建立边界层网格生成的等效PDE方程，利用边界元法精确求解该方程，解决复杂几何情形下已有前沿层进法不够鲁棒的问题。其次，张量尺寸场为各向异性网格方法研究提供了基本的数学工具，基于它和网格局部编辑操作为非结构网格、边界层网格和表面网格的自适应处理建立统一的方法体系。最后，研究高效可靠的并行网格生成方法，实现从“串行网格生成+并行求解”的“准并行”计算流程到“并行网格生成+并行求解”的“全过程并行”CFD流程的跨越。研制自主知识产权的并行自适应CFD求解系统，该系统能有效利用上千个计算核处理包含1亿以上网格点的计算模型。针对内外流场以及可动边界流场计算验证上述CFD方法和软件。

面向飞行器设计中的复杂流动问题，深入开展了各向异性混合网格生成的基础理论和算法研究、软件开发以及方法和软件的验证等工作。在“适应复杂几何外形的边界层网格生成方法”、“各向异性网格自适应局部更新方法”、“大规模网格的并行生成方法”等关键科学问题上取得了多项成体系的原创性成果，包括：① 提出了基于矢量形式拉普拉斯方程的边界层网格生成新方法，开发了控制方程的快速多级边界元求解算法，并将该方法拓展应用于结构网格的自动分区问题；② 基于张量尺寸场和网格编辑操作建立了统一的网格自适应更新方法体系，实现了自适应于流场的各向异性网格自适应局部更新方法；③ 创造性提出两类自动区域分解技术，发展了集并行曲面网格生成、并行实体网格生成以及并行体网格优化于一体的全过程并行网格生成方法体系，解决了十亿以上自由度精细数值模拟与分析面临的计算网格生成难题；④ 提出了可靠高效的并行非结构网格重构方法，发展了面向动边界流场分析动网格生成以及全过程并行模拟等创新方法。基于上述成果研制了自主知识产权的并行自适应CFD求解系统，针对内外流场以及可动边界流场计算验证了方法和软件的正确性和有效性。在国家数值风洞工程、两机专项等重大科技项目的支持下，本项目形成的部分算法和软件已进入实质性应用阶段，为自主可控计算力学软件研发、国家重大和重点型号项目攻关提供了重要支撑。

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