High-Order Mesh Generation and Mesh Adaptation for Complex Geometries with the Open-Source Code NekMesh
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High-fidelity spectral/hp methods possess superior diffusion and dispersion properties than conventional CFD methods and, potentially, better computational efficiency that makes them attractive for the modelling of transient flows about complex industrial geometries. However, these methods rely on high-quality curvilinear boundary-conforming meshes. This is a significant barrier for the industrialisation of the methods, especially when highly stretched meshes are required to model high-Reynolds number viscous flow in the thin boundary layers adjacent to body surfaces. We propose an alternative mesh generation workflow, where the complexity of generating the linear straight-sided mesh is offloaded to a third-party mesh generator and then all high-order activities are performed in NekMesh. This approach allows us to generate curved meshes with the same quality as that of the classical high-order bottom-up approaches [1,2], but takes advantage of the superior flexibility, robustness and user-friendly graphical user interface (GUI) of a state-of-the-art finite volume mesh generator. We present the details of a novel method for an efficient reconstruction of the B-Rep parameterization from the third-party straight-sided mesh that lacks the links to the CAD information needed for the generation of the high-order mesh. We then describe the state-of-the-art techniques employed to generate the high-order, namely mesh curving through projections, surface and volume optimizations with mesh sliding on the CAD B-Rep. We also discuss the use of high-order mesh modification techniques for improving the overall mesh quality in the context of hybrid unstructured meshes. Finally, we present some preliminary results on the application of a posteriori mesh adaptation procedure based on these mesh modification techniques. Two of the SSECOID project automotive test cases, an Inverted Multi-Element Wing and the full Imperial Front Wing, will be used to showcase the capabilities of the proposed high-order mesh generation & adaptation workflow and demonstrate the improved quality of the meshes it generates. [1] M. Turner, J. Peiró, and D. Moxey. Curvilinear mesh generation using a variational framework. Computer-Aided Design, 103:73–91, 2018. [2] M. D. Green, K. S. Kirilov , M.Turner, J. Marcon, J. Eichstäedt, E. Laughton, C. D. Cantwell, S. J. Sherwin, J. Peiró, D. Moxey , NekMesh: An Open-Source High-Order Mesh Generation Framework. SSRN:https://ssrn.com/abstract=4632754