26-11-2012, 02:12 PM
Applied Computational Fluid Dynamics
Applied Computational.ppt (Size: 637.5 KB / Downloads: 616)
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.
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).
Nonconformal mesh
Parametric study of complex geometries.
Nonconformal capability allows you to replace portion of mesh being changed.
Start from 3D boundary mesh or volume mesh.
Add or replace certain parts of mesh.
Remesh volume if necessary.
Mesh naming conventions – cell type
Tri mesh: mesh consisting entirely of triangular elements.
Quad mesh: consists entirely of quadrilateral elements.
Hex mesh: consists entirely of hexahedral elements.
Tet mesh: mesh with only tetrahedral elements.
Hybrid mesh: mesh with one of the following:
Triangles and quadrilaterals in 2D.
Any combination of tetrahedra, prisms, pyramids in 3D.
Boundary layer mesh: prizms at walls and tetrahedra everywhere else.
Hexcore: hexahedra in center and other cell types at walls.
Polyhedral mesh: consists of arbitrary polyhedra.
Nonconformal mesh: mesh in which grid nodes do not match up along an interface.