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1、CFX 5.5 V 5.5.1H 2001AEA Technology71MeshCFX 5.5 V 5.5.1H 2001AEA Technology72IntroductionlCFX5 mesh generator provides: Automatic mesh generation Unstructured triangular surface mesh generation Tetrahedral/prismatic volume mesh generation There are three modes of volume meshing in CFX5 Advancing Fr
2、ont and Inflation (AFI) Paving and Isomeshing Volume Mesh Import (VMI) Mesh adaptionCFX 5.5 V 5.5.1H 2001AEA Technology73Advancing Front and Inflation (AFI) MesherlDeveloped in collaboration with GElThree main components: Surface mesher Inflator (generates surface prisms) Volume mesher (generates te
3、trahedral volume mesh from surface mesh and inflated prismatic elements)lAdvancing Front: CAD surface area discretised and triangular mesh generated New elements generated from advancing “front” of triangles Create tetrahedral elements by point (node) placement Identify exposed faces which now form
4、the new frontlInflation: Allows prismatic elements to be generated by “inflating” triangular surface elementsCFX 5.5 V 5.5.1H 2001AEA Technology74Surface MeshinglSurface meshing Delaunay surface meshing Advancing front (AF) surface meshinglBoth methods are well recognized and have established track
5、records on industrial problemslBoth surface meshers mesh individual surfaceslDefault surface mesher is Delaunay surface mesherCFX 5.5 V 5.5.1H 2001AEA Technology75Surface MeshinglAF is traditionally slower than Delaunay lAF produces higher quality elements at boundarieslAF mesher cannot mesh closed
6、surfaceslAF is less robust on surface meshes with large variation in edge length scale around a surface mesh vertex surfaces with small gapslDelaunay mesh quality is not good on poorly parameterized surfaceslDelaunay works on closed surfacesCFX 5.5 V 5.5.1H 2001AEA Technology76AF .vs. DelaunaySurfac
7、e MeshingDelaunayAF Surface MeshCFX 5.5 V 5.5.1H 2001AEA Technology77AFI Mesher lDomain based surfaces can only be meshed if a fluid domain has been definedlCan view only surface mesh in CFXBuildlSurface and volume mesh automatically generated when definition file is writtenlThe process of setting a
8、n element length scale can be viewed as a 3 step process Assign suitable background length scale (global length scale) Override this locally on surfaces and regions close to them This can be done semiautomatically using curvature sensitivity Override the above two (when necessary) using mesh control
9、sCFX 5.5 V 5.5.1H 2001AEA Technology78AFI MesherlStrengths Good control over surface/volume mesh size Inflation gives good elements in boundary layer Good mesh quality Low memory usage ( Use volume spacing use background length from volume meshing Angular resolution curvature sensitive Relative erro
10、r curvature sensitive Constant constant length scale on all surfaces Target number of nodes to adjust grid spacing Stretch factors for stretching grids Apply proximityCFX 5.5 V 5.5.1H 2001AEA Technology710lSurface mesh parameters Value (degrees) code chooses edge length such that the set angle is su
11、btended at the centre of circle with radius equal to smallest radius of curvature. Default is 18 degrees (recommended 5 to 60 degrees) Value (fraction) deviation of mesh from surface as a fraction of local minimum radius of curvature Minimum edge length lower bound on length scale (default 1% of vol
12、ume background scale) Maximum edge length upper limit on length scale (default same as volume background scale) Volume expansion factor rate of expansion of mesh scale from surface to interiorCurvature Sensitive MeshCFX 5.5 V 5.5.1H 2001AEA Technology711Without surface curvature sensitive meshingWit
13、h surface curvature sensitive meshing.Curvature Sensitive Mesh ExamplesCFX 5.5 V 5.5.1H 2001AEA Technology712Proximity Sensitivity in Surface MeshWith proximity featureWithout proximity featurelEdge Proximity is used to automatically modify mesh elements in regions where curved and flat surfaces are
14、 in close proximity Bounding curves of surface “sense” nearby curves and increase mesh density locallyCFX 5.5 V 5.5.1H 2001AEA Technology713Proximity Sensitivity in Surface MeshlSurface Proximity is used to automatically reduces the mesh size in regions where surfaces are in close proximity and the
15、original mesh does not resolve the gap sufficiently. CFX 5.5 V 5.5.1H 2001AEA Technology714Mesh ControlslMesh Controls Act as sources which reduce the local element edge length scale Location defined using any valid CFXBuild point/surface description Can be of the following types: Point Line Triangle Surface CFX 5.5 V 5.5.1H 2001AEA Technology715Mesh ControlsPointLineTriangleCFX 5.5 V 5.5.1H 2001AEA Technology716Mesh ControlslMesh Controls: Influence controlled by mesh control values Local element length scale Radius region of fixed local element length scale from mesh control
