07-mesh

# 07-mesh - Lecture 7 Meshing Applied Computational Fluid...

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1 Lecture 7 - Meshing Applied Computational Fluid Dynamics Instructor: André Bakker © André Bakker (2002-2006) © Fluent Inc. (2002)

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2 Outline Why is a grid needed? Element types. Grid types. Grid design guidelines. Geometry. Solution adaption. Grid import.
3 Why is a grid needed? The grid: Designates the cells or elements on which the flow is solved. Is a discrete representation of the geometry of the problem. Has cells grouped into boundary zones where b.c.’s are applied. The grid has a significant impact on: Rate of convergence (or even lack of convergence). Solution accuracy. CPU time required. Importance of mesh quality for good solutions. Grid density. Adjacent cell length/volume ratios. Skewness. Tet vs. hex. Boundary layer mesh. Mesh refinement through adaption.

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4 Geometry can be very simple... … or more complex geometry for a “cube” Geometry The starting point for all problems is a “geometry.” The geometry describes the shape of the problem to be analyzed. Can consist of volumes, faces (surfaces), edges (curves) and vertices (points).
5 Geometry creation Geometries can be created top-down or bottom-up. Top-down refers to an approach where the computational domain is created by performing logical operations on primitive shapes such as cylinders, bricks, and spheres. Bottom-up refers to an approach where one first creates vertices (points), connects those to form edges (lines), connects the edges to create faces, and combines the faces to create volumes. Geometries can be created using the same pre-processor software that is used to create the grid, or created using other programs (e.g. CAD, graphics).

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6 Typical cell shapes Many different cell/element and grid types are available. Choice depends on the problem and the solver capabilities. Cell or element types: 2D: 3D: triangle ( “tri” ) 2D prism ( quadrilateral or “quad” ) tetrahedron ( “tet” ) pyramid prism with quadrilateral base ( hexahedron or “hex” ) prism with triangular base ( wedge ) arbitrary polyhedron
7 node face cell face cell node edge 2D computational grid 3D computational grid cell center Terminology Cell = control volume into which domain is broken up. Node = grid point. Cell center = center of a cell. Edge = boundary of a face. Face = boundary of a cell. Zone = grouping of nodes, faces, and cells: Wall boundary zone. Fluid cell zone. Domain = group of node, face and cell zones.

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8 Grid types: structured grid Single-block, structured grid. i,j,k indexing to locate neighboring cells. Grid lines must pass all through domain. Obviously can’t be used for very complicated geometries.
9 Different types of hexahedral grids.

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• Fall '10
• N/A
• Mesh, Unstructured grid, Skewness Cell Quality

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