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[snappyHexMesh] snappyHexMesh Boundary Layer at Corner |
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September 24, 2013, 16:49 |
snappyHexMesh Boundary Layer at Corner
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Peng Zhong
Join Date: Jun 2013
Posts: 12
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Hi OpenFoam users, I am using snappyHexMesh in OF2.2.1 to generate a mesh of a duct. Everything is fine except the layers at the corner of the duct always shrink in thickness. I have tried changing the featureAngle in addlayers section and it does seem to help a bit. But the best result I have obtained from changing featureAngle still has corner layers shrinking a bit. Below is my snappyHexMesh code. Please also see the attached picture generated by this code. Thank you very much
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.2.1 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object snappyHexMeshDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // // Which of the steps to run castellatedMesh true; snap true; addLayers true; // Geometry. Definition of all surfaces. All surfaces are of class // searchableSurface. // Surfaces are used // - to specify refinement for any mesh cell intersecting it // - to specify refinement for any mesh cell inside/outside/near // - to 'snap' the mesh boundary to the surface geometry { nozzle.stl { type triSurfaceMesh; //tolerance 1E-5; // optional:non-default tolerance on intersections //maxTreeDepth 10; // optional:depth of octree. Decrease only in case // of memory limitations. // Per region the patchname. If not provided will be <name>_<region>. regions { } } }; // Settings for the castellatedMesh generation. castellatedMeshControls { // Refinement parameters // ~~~~~~~~~~~~~~~~~~~~~ // If local number of cells is >= maxLocalCells on any processor // switches from from refinement followed by balancing // (current method) to (weighted) balancing before refinement. maxLocalCells 1000000; // Overall cell limit (approximately). Refinement will stop immediately // upon reaching this number so a refinement level might not complete. // Note that this is the number of cells before removing the part which // is not 'visible' from the keepPoint. The final number of cells might // actually be a lot less. maxGlobalCells 5000000; // The surface refinement loop might spend lots of iterations refining just a // few cells. This setting will cause refinement to stop if <= minimumRefine // are selected for refinement. Note: it will at least do one iteration // (unless the number of cells to refine is 0) minRefinementCells 0; // Allow a certain level of imbalance during refining // (since balancing is quite expensive) // Expressed as fraction of perfect balance (= overall number of cells / // nProcs). 0=balance always. maxLoadUnbalance 0.10; // Number of buffer layers between different levels. // 1 means normal 2:1 refinement restriction, larger means slower // refinement. nCellsBetweenLevels 5; // Explicit feature edge refinement // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Specifies a level for any cell intersected by explicitly provided // edges. // This is a featureEdgeMesh, read from constant/triSurface for now. // Specify 'levels' in the same way as the 'distance' mode in the // refinementRegions (see below). The old specification // level 2; // is equivalent to // levels ((0 2)); features ( /* { // file "nozzle.eMesh"; // level 1; // levels ((0.0 0)); } */ ); // Surface based refinement // ~~~~~~~~~~~~~~~~~~~~~~~~ // Specifies two levels for every surface. The first is the minimum level, // every cell intersecting a surface gets refined up to the minimum level. // The second level is the maximum level. Cells that 'see' multiple // intersections where the intersections make an // angle > resolveFeatureAngle get refined up to the maximum level. refinementSurfaces { nozzle.stl { // Surface-wise min and max refinement level level (0 0); //- Optional angle to detect small-large cell situation // perpendicular to the surface. Is the angle of face w.r.t. // the local surface normal. Use on flat(ish) surfaces only. // Otherwise leave out or set to negative number. //perpendicularAngle 10; //- Optional faceZone and (for closed surface) cellZone with // how to select the cells that are in the cellZone // (inside / outside / specified insidePoint) //faceZone sphere; //cellZone sphere; //cellZoneInside inside; //outside/insidePoint //- Optional specification of what to do with faceZone faces: // internal : keep them as internal faces (default) // baffle : create baffles from them. This gives more // freedom in mesh motion // boundary : create free-standing boundary faces (baffles // but without the shared points) //faceType baffle; } } // Feature angle: // - used if min and max refinement level of a surface differ // - used if feature snapping (see snapControls below) is used resolveFeatureAngle 60; // Region-wise refinement // ~~~~~~~~~~~~~~~~~~~~~~ // Specifies refinement level for cells in relation to a surface. One of // three modes // - distance. 'levels' specifies per distance to the surface the // wanted refinement level. The distances need to be specified in // increasing order. // - inside. 'levels' is only one entry and only the level is used. All // cells inside the surface get refined up to the level. The surface // needs to be closed for this to be possible. // - outside. Same but cells outside. refinementRegions { nozzle.stl { mode distance; levels ((0.002 2) (0.004 1)); // levels ((1.0 5) (2.0 3)); } } // Mesh selection // ~~~~~~~~~~~~~~ // After refinement patches get added for all refinementSurfaces and // all cells intersecting the surfaces get put into these patches. The // section reachable from the locationInMesh is kept. // NOTE: This point should never be on a face, always inside a cell, even // after refinement. locationInMesh (0 0 0); // Whether any faceZones (as specified in the refinementSurfaces) // are only on the boundary of corresponding cellZones or also allow // free-standing zone faces. Not used if there are no faceZones. allowFreeStandingZoneFaces true; } // Settings for the snapping. snapControls { // Number of patch smoothing iterations before finding correspondence // to surface nSmoothPatch 3;//3; // Maximum relative distance for points to be attracted by surface. // True distance is this factor times local maximum edge length. // Note: changed(corrected) w.r.t 17x! (17x used 2* tolerance) tolerance 1.0;//2.0; // Number of mesh displacement relaxation iterations. nSolveIter 50;//200;//30; // Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. nRelaxIter 5;//5; // Feature snapping // Number of feature edge snapping iterations. // Leave out altogether to disable. nFeatureSnapIter 10;//50; // Detect (geometric only) features by sampling the surface // (default=false). implicitFeatureSnap true; // Use castellatedMeshControls::features (default = true) explicitFeatureSnap false; // Detect features between multiple surfaces // (only for explicitFeatureSnap, default = false) multiRegionFeatureSnap false; } // Settings for the layer addition. addLayersControls { // Are the thickness parameters below relative to the undistorted // size of the refined cell outside layer (true) or absolute sizes (false). relativeSizes false; // Layer thickness specification. This can be specified in one of four ways // - expansionRatio and finalLayerThickness (cell nearest internal mesh) // - expansionRatio and firstLayerThickness (cell on surface) // - overall thickness and firstLayerThickness // - overall thickness and finalLayerThickness // Expansion factor for layer mesh expansionRatio 1.2; // Wanted thickness of the layer furthest away from the wall. // If relativeSizes this is relative to undistorted size of cell // outside layer. //finalLayerThickness 0.3; // Wanted thickness of the layer next to the wall. // If relativeSizes this is relative to undistorted size of cell // outside layer. firstLayerThickness 0.000089; // Wanted overall thickness of layers. // If relativeSizes this is relative to undistorted size of cell // outside layer. //thickness 0.5 // Minimum overall thickness of total layers. If for any reason layer // cannot be above minThickness do not add layer. // If relativeSizes this is relative to undistorted size of cell // outside layer.. minThickness 0.000089;//0.5; // Per final patch (so not geometry!) the layer information // Note: This behaviour changed after 21x. Any non-mentioned patches // now slide unless: // - nSurfaceLayers is explicitly mentioned to be 0. // - angle to nearest surface < slipFeatureAngle (see below) // Disable any mesh shrinking and layer addition on any point of // a patch by setting nSurfaceLayers to 0 layers { nozzle.stl_Combustor_ASCII { nSurfaceLayers 9; // Per patch layer data // expansionRatio 1.3; // finalLayerThickness 0.3; // minThickness 0.1; } } // If points get not extruded do nGrow layers of connected faces that are // also not grown. This helps convergence of the layer addition process // close to features. // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x) nGrow 0; // Advanced settings // When not to extrude surface. 0 is flat surface, 90 is when two faces // are perpendicular featureAngle 360; // At non-patched sides allow mesh to slip if extrusion direction makes // angle larger than slipFeatureAngle. slipFeatureAngle 20;//20; // Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. nRelaxIter 5; // Number of smoothing iterations of surface normals nSmoothSurfaceNormals 5;//1; // Number of smoothing iterations of interior mesh movement direction nSmoothNormals 3; // Smooth layer thickness over surface patches nSmoothThickness 10; // Stop layer growth on highly warped cells maxFaceThicknessRatio 0.5; // Reduce layer growth where ratio thickness to medial // distance is large maxThicknessToMedialRatio 1000; // Angle used to pick up medial axis points // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130 in 17x. minMedianAxisAngle 300; // Create buffer region for new layer terminations nBufferCellsNoExtrude 0; // Overall max number of layer addition iterations. The mesher will exit // if it reaches this number of iterations; possibly with an illegal // mesh. nLayerIter 50; // Max number of iterations after which relaxed meshQuality controls // get used. Up to nRelaxedIter it uses the settings in // meshQualityControls, // after nRelaxedIter it uses the values in // meshQualityControls::relaxed. nRelaxedIter 20; // Additional reporting: if there are just a few faces where there // are mesh errors (after adding the layers) print their face centres. // This helps in tracking down problematic mesh areas. additionalReporting true; } // Generic mesh quality settings. At any undoable phase these determine // where to undo. meshQualityControls { // Maximum non-orthogonality allowed. Set to 180 to disable. maxNonOrtho 65;//65; // Max skewness allowed. Set to <0 to disable. maxBoundarySkewness 20;//20; maxInternalSkewness 4;//4; // Max concaveness allowed. Is angle (in degrees) below which concavity // is allowed. 0 is straight face, <0 would be convex face. // Set to 180 to disable. maxConcave 80;//80; // Minimum pyramid volume. Is absolute volume of cell pyramid. // Set to a sensible fraction of the smallest cell volume expected. // Set to very negative number (e.g. -1E30) to disable. minVol 1e-13; // Minimum quality of the tet formed by the face-centre // and variable base point minimum decomposition triangles and // the cell centre. This has to be a positive number for tracking // to work. Set to very negative number (e.g. -1E30) to // disable. // <0 = inside out tet, // 0 = flat tet // 1 = regular tet minTetQuality 1e-9; // Minimum face area. Set to <0 to disable. minArea -1; // Minimum face twist. Set to <-1 to disable. dot product of face normal // and face centre triangles normal minTwist 0.05; // minimum normalised cell determinant // 1 = hex, <= 0 = folded or flattened illegal cell minDeterminant 0.001; // minFaceWeight (0 -> 0.5) minFaceWeight 0.05; // minVolRatio (0 -> 1) minVolRatio 0.01; // must be >0 for Fluent compatibility minTriangleTwist -1; //- if >0 : preserve single cells with all points on the surface if the // resulting volume after snapping (by approximation) is larger than // minVolCollapseRatio times old volume (i.e. not collapsed to flat cell). // If <0 : delete always. //minVolCollapseRatio 0.5; // Advanced // Number of error distribution iterations nSmoothScale 4; // amount to scale back displacement at error points errorReduction 0.75; // Optional : some meshing phases allow usage of relaxed rules. // See e.g. addLayersControls::nRelaxedIter. relaxed { //- Maximum non-orthogonality allowed. Set to 180 to disable. maxNonOrtho 75; } } // Advanced // Flags for optional output // 0 : only write final meshes // 1 : write intermediate meshes // 2 : write volScalarField with cellLevel for postprocessing // 4 : write current intersections as .obj files debug 0; // Merge tolerance. Is fraction of overall bounding box of initial mesh. // Note: the write tolerance needs to be higher than this. mergeTolerance 1e-6; // ************************************************** *********************** // |
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