How to Do External Mesh for Airfoil sHM

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September 22, 2012, 15:59
How to Do External Mesh for Airfoil sHM
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Eric R
Join Date: Jul 2012
Posts: 82
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I am trying to mesh an airfoil shape in OF 2.0.0 using sHM from an .stl file. Once I run snappyHexMesh, it meshes the internal geometry only and cuts out the rest of the bounding blockMesh. How do I simply cut out the shape of the airfoil from the block?

Should locationInMesh be a point inside the .stl geometry for this case, or should it be somewhere outside (but still within the blockMesh)?
Quote:
 convertToInches 1; vertices ( (1 -50 -50) (2 -50 -50) (2 10 -50) (1 10 -50) (1 -50 50) (2 -50 50) (2 10 50) (1 10 50) //(-1 -50 -10) //(5 -50 -10) //(5 -50 10) //(-1 -50 10) //(-1 5 -10) //(5 5 -10) //(5 5 10) //(-1 5 10) ); blocks ( hex (0 1 2 3 4 5 6 7) (1 200 100) simpleGrading (1 1 1) ); edges ( ); boundary ( topAndBottom { type patch; faces ( (4 5 6 7) (0 1 2 3) ); } inlet { type patch; faces ( (3 2 6 7) ); } outlet { type patch; faces ( (0 1 5 4) ); } front { type empty; faces ( (1 2 6 5) ); } back { type empty; faces ( (0 3 7 4) ); } ); mergePatchPairs ( ); // ************************************************** *********************** //
Quote:
 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 { airfoil.stl { type triSurfaceMesh; name airfoil; } refinementBox { type searchableBox; min (-1 -1 -1); max ( 5 5 5); } }; // 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 2500000; // 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 10000000; // 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; // Number of buffer layers between different levels. // 1 means normal 2:1 refinement restriction, larger means slower // refinement. nCellsBetweenLevels 8; // Explicit feature edge refinement // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // Specifies a level for any cell intersected by its edges. // This is a featureEdgeMesh, read from constant/triSurface for now. features ( { file "airfoil.eMesh"; level 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 { airfoil { // Surface-wise min and max refinement level level (4 4); } } // Resolve sharp angles on fridges resolveFeatureAngle 30; // 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 // descending 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 { refinementBox { mode inside; levels ((1e15 2)); } } // 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 (1 -20 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; //- Relative distance for points to be attracted by surface feature point // or edge. True distance is this factor times local // maximum edge length. tolerance 4.0; //- Number of mesh displacement relaxation iterations. nSolveIter 30; //- Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. nRelaxIter 5; //- Highly experimental and wip: number of feature edge snapping // iterations. Leave out altogether to disable. nFeatureSnapIter 10; } // 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 true; // Per final patch (so not geometry!) the layer information layers { "airfoil.*" { nSurfaceLayers 2; } } // Expansion factor for layer mesh expansionRatio 1.2; //- Wanted thickness of final added cell layer. If multiple layers // is the // thickness of the layer furthest away from the wall. // Relative to undistorted size of cell outside layer. // is the thickness of the layer furthest away from the wall. // See relativeSizes parameter. finalLayerThickness 0.6; //- Minimum thickness of cell layer. If for any reason layer // cannot be above minThickness do not add layer. // Relative to undistorted size of cell outside layer. // See relativeSizes parameter. 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 // make straight angle. featureAngle 60; //- Maximum number of snapping relaxation iterations. Should stop // before upon reaching a correct mesh. nRelaxIter 5; // Number of smoothing iterations of surface normals nSmoothSurfaceNormals 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 0.3; // Angle used to pick up medial axis points // Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x. minMedianAxisAngle 90; // 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; } // Generic mesh quality settings. At any undoable phase these determine // where to undo. meshQualityControls { //- Maximum non-orthogonality allowed. Set to 180 to disable. maxNonOrtho 45; //- Max skewness allowed. Set to <0 to disable. maxBoundarySkewness 2; maxInternalSkewness 2; //- 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; //- 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. Set to very negative number (e.g. -1E30) to // disable. // <0 = inside out tet, // 0 = flat tet // 1 = regular tet minTetQuality 1e-30; //- 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; // Advanced //- Number of error distribution iterations nSmoothScale 4; //- amount to scale back displacement at error points errorReduction 0.75; } // 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; // ************************************************** *********************** //

Last edited by msuaeronautics; September 22, 2012 at 16:26.

 September 23, 2012, 04:00 #2 Member   Jan Join Date: Dec 2009 Location: Berlin Posts: 50 Rep Power: 9 locationInMesh is a location in the mesh ... actually where YOU want the mesh to be! So if you want the mesh outside the stl ... then a locationInMesh would be outside your stl-geometry (of course the location should still be inside your blockmesh - if it isn't snappy will tell you). __________________ ~~~_/)~~~

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