Fluent is an unstructured solver. It uses internal data structures toassign an order to the cells, faces, and grid points in a mesh and tomaintain contactbetween adjacentcells.Therefore, it does not require i, j, k indexing to locate neighboring cells.This gives us the flexibility to use the best mesh topology for our problem,as the solver does not force an overall structure or topology on the mesh.31/253
31/253 Fluent is an unstructured solver. It uses internal data structures to assign an order to the cells, faces, and grid points in a mesh and to maintain contact between adjacent cells. Therefore, it does not require i, j, k indexing to locate neighboring cells. This gives us the flexibility to use the best mesh topology for our problem, as the solver does not force an overall structure or topology on the mesh
ExamplesofAcceptableMeshTopologiesUnstructured QuadStructured Quad Mesh foranMultiblockStructuredOuadMeshMeshAirfoilUnstructuredTriangularParachuteModeled WithZero-HybridTri/QuadMeshwithMeshfor anAirfoilThicknessWallHanging Nodes32/253
32/253 Examples of Acceptable Mesh Topologies Structured Quad Mesh for an Airfoil Unstructured Quad Mesh Multiblock Structured Quad Mesh Parachute Modeled With ZeroThickness Wall Unstructured Triangular Mesh for an Airfoil Hybrid Tri/Quad Mesh with Hanging Nodes
ChoosingtheAppropriate MeshTypeFluent can use meshes comprised of triangular or quadrilateral cells (or acombination of the two) in 2D domain, and tetrahedral, hexahedralpolyhedral, pyramid, or wedge cells (or a combination of these) in 3DdomainThe choice of which mesh type to use will depend on the actualapplication.When choosing mesh type, considerthefollowingissues:SetuptimeComputationalexpenseNumerical diffusion(false diffusion)(Chapter5.5,P.152)33/253
33/253 Choosing the Appropriate Mesh Type Fluent can use meshes comprised of triangular or quadrilateral cells (or a combination of the two) in 2D domain, and tetrahedral, hexahedral, polyhedral, pyramid, or wedge cells (or a combination of these) in 3D domain. ① Setup time The choice of which mesh type to use will depend on the actual application. When choosing mesh type, consider the following issues: ② Computational expense ③ Numerical diffusion(false diffusion)(Chapter 5.5, P.152)
(1)SetupTimeMany flow problems solved in engineering practice involve complexgeometries.. The creation of structured or block-structured meshes(consisting of quadrilateral or hexahedral elements) for such problems canbeextremelytime-consumingTherefore, setup time for complex geometries is the majormotivation for using unstructured meshes employing triangular ortetrahedral cells.However, if the geometry is relatively simple, theremay be no saving in setup time with either approach.34/253
34/253 Many flow problems solved in engineering practice involve complex geometries. The creation of structured or block-structured meshes (consisting of quadrilateral or hexahedral elements) for such problems can be extremely time-consuming. Therefore, setup time for complex geometries is the major motivation for using unstructured meshes employing triangular or tetrahedral cells. However, if the geometry is relatively simple, there may be no saving in setup time with either approach. (1) Setup Time
Other risks of using structured or block-structured meshes withcomplicated geometries include the oversimplification of thegeometry, mesh quality issues, and a less efficient meshdistribution(for example, fine resolution in areas of lessimportance)that results in a high cell count.(2)ComputationalExpenseWhen geometries are complex or the range of length scales ofthe flow is large, a triangular/tetrahedral mesh can be createdwith far fewer cells than the equivalent mesh consisting ofquadrilateral/hexahedralelements.JJi253
35/253 Other risks of using structured or block-structured meshes with complicated geometries include the oversimplification of the geometry, mesh quality issues, and a less efficient mesh distribution(for example, fine resolution in areas of less importance) that results in a high cell count. (2) Computational Expense When geometries are complex or the range of length scales of the flow is large, a triangular/tetrahedral mesh can be created with far fewer cells than the equivalent mesh consisting of quadrilateral/hexahedral elements