Algorithms for Geometry-Adapted Mesh Refinement with Cell Stack Preservation in the FlowSimulator

Abstract

Adaptive mesh refinement allows Computational-Fluid-Dynamics (CFD) simulations to obtain faster solutions with more accuracy. However, given a refinement indicator field, a pure threshold-based refinement of individual cells is not enough. Under refinement, the boundary of the mesh has to converge to the true geometry, while high-quality boundary layer meshes must be maintained for high-Reynolds-number flows. Here we propose a FlowSimulator-based in-memory process chain for geometry-adapted mesh refinement with cell-stack-preservation. The process chain can seamlessly be integrated into previous CFD scenarios, since it deals with existing meshes and geometries without requiring control over the meshing process. It combines the FlowSimulator DataManager (FSDM) with several FlowSimulator plug-ins, including the high-order, highly-parallelized CFD Software by ONERA, DLR and Airbus (CODA). This work focuses on the plug-ins for mesh refinement, FSAdaptationNG, and Computational Aided Design (CAD) based geometry-handling, FSOCCT. FSAdaptationNG is a volume-cell-driven hierarchical nonconforming mesh refinement tool for fully unstructured storage. It is designed to satisfy the requirements of FlowSimulator in general and CODA in particular. To be applicable to CFD-simulations with boundary layers, it features cell stack-oriented refinement. FSOCCT gives access to some functionalities of the CAD-kernel Open CASCADE Technology (OCCT) to the FlowSimulator. In addition, it implements a meta-data-based mapping between mesh objects and the CAD model. By using vendor-neutral CAD-formats and mesh formats available in the FSDM, it is independent of a specific modeling or meshing tool, and works with the available meta-data using similarities between the hierarchical structure of CAD models and meshes with defined boundary conditions. The reliability of the process chain is demonstrated by application to test cases from the aerospace industry. Results showed that geometry-adapted mesh refinement with cell-stack preservation enables recovering the original geometry during refinement.