PostBL: Post-mesh Boundary Layer Mesh Generation Tool

Abstract

Abstract.A boundary layer mesh is a mesh with dense element distribution in the normal direction along specific boundaries. PostBL is a utility to generate boundary layer elements on an existing mesh model. PostBL supports creation of hexahedral, prism, quad, and tri boundary layer elements. It is formulated as an algorithm in MeshKit, which is an open-source library for mesh generation functionalities. Typically, boundary layer mesh generation is a premeshing process; in this effort, however, we start from a model that has already been meshed. Boundary layer elements can be generated along the entire skin or on selected exterior or internal surface boundaries. PostBL mesh operation can be coupled with other MeshKit meshing operations such as Jaal, NetGen, TetGen, and CAMAL and custom meshing tools such as RGG. Simple examples demonstrating generation of boundary layers on different mesh types and the OECD Vattenfall T-Junction benchmark hexahedral mesh are presented. IntroductionBoundary layers are typically used for CFD applications, in regions with strong gradients-turbulent flow, diffusion-type equations, laminar flow or no-slip boundary with strong gradient of velocity [23]. Most other tools for generating boundary layers insert them before bulk mesh generation; in this effort, however, we develop a tool called PostBL and start from an already meshed model. This strategy is particularly useful when the meshing of the original problem is complicated and involves geometry decomposition and other geometry modifications prior to meshing. A utility for adding layers of elements along the exterior or interior (shared by two materials) boundary is developed. It relies on the edge or surface (2D or 3D) mesh on which the boundary layer elements are desired. This method is also useful for creating boundary layer elements in the wake regions along the direction of fluid flow. After boundary layer insertion, smoothing can optionally be used to improve mesh quality. Typically in external aerodynamic simulations, the type of turbulent modeling decides the thickness and number of boundary layer elements; PostBL would save time and eliminate the complexity involved in remeshing the entire model.

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“…PostBL(Post mesh Boundary Layer) [3] MeshOp (mesh operation), which generates boundary layer meshes for an already existing mesh model was integrate with RGG GUI application. Figure 1 shows a di-graph based representation for meshing of reactor assembly, Stage 1 (AssyGen) and stage 2 (Meshing) of the three stage RGG workflow [4] (third stage is CoreGen) are shown in Figure 2, where meshing is handled by the AssyMesher MeshOp in MeshKit.…”

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“…The embedded boundary meshing [9] tool generates Cartesian meshes for solvers that use embedded boundary algorithms 4. The post mesh boundary layer [4] generates boundary layer meshes for an already existing mesh model (post-processing after mesh-generation), which has proven to be powerful for several CFD applications. 5.…”