CFD Online Discussion Forums - [snappyHexMesh] Problem in results with snappyHexMesh between refinement levels

fvSchemes

ddtSchemes
{
default Euler;
}

gradSchemes
{
default leastSquares;
}

divSchemes
{
default none;
div(phi,U) Gauss linearUpwindV grad(U);
div(phi,k) Gauss upwind;
div(phi,kl) Gauss upwind;
div(phi,kt) Gauss upwind;
div(phi,omega) Gauss upwind;
div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

wallDist
{
method meshWave;
}

fvSolution

solvers
{
p
{
solver GAMG;
tolerance 1e-6;
//relTol 0.01;
smoother GaussSeidel;
nPreSweeps 0;
nPostSweeps 1;
nFinestSweeps 2;
cacheAgglomeration true;
nCellsInCoarsestLevel 20;
agglomerator faceAreaPair;
mergeLevels 1;
}

pFinal
{
$p;
tolerance 1e-06;
relTol 0;
}

"(U|k|kl|kt|omega)"
{
solver GAMG;
smoother GaussSeidel;
tolerance 1e-06;
//relTol 0.01
nPreSweeps 0;
nPostSweeps 1;
nFinestSweeps 2;
cacheAgglomeration true;
nCellsInCoarsestLevel 20;
agglomerator faceAreaPair;
mergeLevels 1;
}

"(U|k|kl|kt|omega)Final"
{
$U;
tolerance 1e-06;
relTol 0;
}
}

PISO
{
nOuterCorrectors 1;
nCorrectors 2;
nNonOrthogonalCorrectors 1;
pRefCell 0;
pRefValue 0;
}

relaxationFactors
{
equations
{
p 0.3; // 0.9 is more stable but 0.95 more convergent
"(U|k|kl|kt|omega)" 0.7; // 0.9 is more stable but 0.95 more convergent
}
}

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
{
Estate_quer_3d.stl
{
type triSurfaceMesh;
name estate;
}

//- Refine a bit extra around the small centre hole
refinebox
{
type searchableBox;
min (-500.0 0 -80);
max (3000 1000 500);
}

refinebox1
{
type searchableBox;
min (-300 0 -80);
max (1000 1000 450);
}
refinebox2
{
type searchableBox;
min (-200 0 -80);
max (800 1000 400);
}
};

// 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 20000000;

// 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 20;

// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 10;

// 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 "Estate_quer_3d.extendedFeatureEdgeMesh";
level 7;
}
);

// 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
{
estate
{
// Surface-wise min and max refinement level
level (7 7);
}
}

resolveFeatureAngle 90;

// 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
{
refinebox
{
mode inside;
levels ((1E15 2));
}

refinebox1
{
mode inside;
levels ((1E15 3));
}
refinebox2
{
mode inside;
levels ((1E15 4));
}
}

// 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.
// This is an outside point locationInMesh (-0.033 -0.033 0.0033);
locationInMesh (2100 0.1 700); // Inside point

// 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 1.0;

//- Number of mesh displacement relaxation iterations.
nSolveIter 300;

//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;

// Feature snapping

//- Number of feature edge snapping iterations.
// Leave out altogether to disable.
nFeatureSnapIter 10;

//- Detect (geometric) features by sampling the surface
implicitFeatureSnap false;

//- Use castellatedMeshControls::features
explicitFeatureSnap true;

//- Detect features between multiple surfaces
// (only for explicitFeatureSnap, default = false)
multiRegionFeatureSnap true;
}

// 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
{
estate
{
nSurfaceLayers 3;
}
}

// 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.
// See relativeSizes parameter.
finalLayerThickness 0.5;

// Minimum thickness of cell layer. If for any reason layer
// cannot be above minThickness do not add layer.
// See relativeSizes parameter.
minThickness 0.25;

// 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.
nGrow 0;

// Advanced settings

// When not to extrude surface. 0 is flat surface, 90 is when two faces
// are perpendicular
featureAngle 70;

// 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
minMedianAxisAngle 120;

// 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 5;

// Max number of iterations after which relaxed meshQuality controls
// get used. Up to nRelaxIter it uses the settings in meshQualityControls,
// after nRelaxIter it uses the values in meshQualityControls::relaxed.
nRelaxedIter 20;
}