[Steven Chew]

Hi all,

Need some assistance here. I virtually copied the Motorbike case from the tutorial and tried to run using my own vehicle geometry. My case consists of an inlet uniform flow (22m/s) with pressure boundary outlet, and all 4 side walls including the stationary floor.

Running wise I got no problem, and I was able to run snappyHexMesh and simpleFoam and get some results. But when I checked the central cut plane U contour plot, this appears



At the entrance and exit area the velocity magnitude seem to be pretty smooth along the ground, but as it approaches even the first refined mesh, there is this jagged contours.

I do not really understand, and I have checked the motorbike case. The flow parameters I have used including the turbulence numbers are all the same. There are also jagged contour along the ground but it seems more controlled under a thinner layer.

I was suspecting should I increase the number of buffer layers? below is my snappyHexMeshdict file

FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

castellatedMesh true;
snap true;
addLayers true;

geometry
{
sunspec.stl
{
type triSurfaceMesh;
name sunspec;
}

refinementBox
{
type searchableBox;
min (-4000.0 -600.0 -1400.0);
max ( 8000.0 1000.0 1400.0);
}
};

// Settings for the castellatedMesh generation.
castellatedMeshControls
{
maxLocalCells 3000000;

maxGlobalCells 3000000;

minRefinementCells 10;

maxLoadUnbalance 0.10;

nCellsBetweenLevels 3;

features
(
);

// Surface based refinement
refinementSurfaces
{
sunspec
{
level (5 6);
}
}

// Resolve sharp angles
resolveFeatureAngle 30;

refinementRegions
{
refinementBox
{
mode inside;
levels ((1E15 4));
}
}


// Mesh selection
// ~~~~~~~~~~~~~~
locationInMesh (9700 1700 2100);

allowFreeStandingZoneFaces true;
}

// Settings for the snapping.
snapControls
{
nSmoothPatch 4;

tolerance 4.0;

nSolveIter 20;

nRelaxIter 5;
}

// Settings for the layer addition.
addLayersControls
{
relativeSizes true;

layers
{
"(walls|sunspec).*"
{
nSurfaceLayers 1;
}
}

// Expansion factor for layer mesh
expansionRatio 1.0;
finalLayerThickness 0.3;

minThickness 0.1;

nGrow 0;

featureAngle 30;

nRelaxIter 3;

nSmoothSurfaceNormals 1;

nSmoothNormals 3;

nSmoothThickness 10;

maxFaceThicknessRatio 0.5;

maxThicknessToMedialRatio 0.3;

minMedianAxisAngle 90;

nBufferCellsNoExtrude 0;

nLayerIter 50;
}

meshQualityControls
{
maxNonOrtho 65;

maxBoundarySkewness 20;
maxInternalSkewness 4;

maxConcave 80;

minVol 1e-13;

minTetQuality 1e-30;

minArea -1;

minTwist 0.02;

minDeterminant 0.001;

minFaceWeight 0.02;

minVolRatio 0.01;

minTriangleTwist -1;


// Advanced
nSmoothScale 4;
errorReduction 0.75;
}

// Advanced
debug 0;
mergeTolerance 1e-6;


// ************************************************** *********************** //