CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Native Meshers: snappyHexMesh and Others

SnappyHexMesh doesn't succeed in adding several layers

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree2Likes
  • 1 Post By eti0123456789
  • 1 Post By eti0123456789

Reply
 
LinkBack Thread Tools Display Modes
Old   May 2, 2010, 13:24
Default SnappyHexMesh doesn't succeed in adding several layers
  #1
New Member
 
Etienne T.
Join Date: Feb 2010
Posts: 3
Rep Power: 6
eti0123456789 is on a distinguished road
Hello,

I am using SnappyHexMesh with OF 1.6 to study a simple 2D wing. In order to use SnappyHexMesh, it is in fact a 3D case with a thin "wind tunnel". But SnappyHexMesh doesn't succeed in adding several layers in the boundary layer, it only creates one :

I tried to reduce constraints on mesh quality but this doesn't work.

Here is the addLayerControls :
Quote:
addLayersControls
{
relativeSizes true;

// Per final patch (so not geometry!) the layer information
layers
{
"aile.*"
{
nSurfaceLayers 10;
}
}

// Expansion factor for layer mesh
expansionRatio 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.
finalLayerThickness 0.5;

//- 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.
minThickness 0.00000001;

//- 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 10;


// Advanced settings

//- When not to extrude surface. 0 is flat surface, 90 is when two faces
// make straight angle.
featureAngle 0;

//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 10;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 5;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 15;

// Smooth layer thickness over surface patches
nSmoothThickness 20;

// Stop layer growth on highly warped cells
maxFaceThicknessRatio 1000000000;

// Reduce layer growth where ratio thickness to medial
// distance is large
maxThicknessToMedialRatio 10000000;

// Angle used to pick up medial axis points
minMedianAxisAngle 130;

// Create buffer region for new layer terminations
nBufferCellsNoExtrude 10;

// Overall max number of layer addition iterations
nLayerIter 50;
}
Can someone help me ?
Attached Images
File Type: png layer.png (6.7 KB, 630 views)
eti0123456789 is offline   Reply With Quote

Old   May 4, 2010, 04:21
Default
  #2
Member
 
Moritz Wied
Join Date: Mar 2010
Location: suttgart, germany
Posts: 35
Rep Power: 6
Mo-ITB is on a distinguished road
hi,

did you try to decrease the expansionratio and the finallayerthickness?
im having quite similar problems at the moment, if you find some good ideas,let us know .
Mo-ITB is offline   Reply With Quote

Old   May 15, 2010, 09:41
Default
  #3
New Member
 
Etienne T.
Join Date: Feb 2010
Posts: 3
Rep Power: 6
eti0123456789 is on a distinguished road
I have found an idea, and that works quite well : firstly, I use SHM to make a thick layer, and then, I write a little bash script which uses the refineWallLayer tool to split the boundary layer. Here is the script :
Code:
for i in `seq 1 5`;
do
	refineWallLayer -overwrite name_of_the_patch 0.7;
done
But if anybody knows how to solve this problem using directly SHM, please help !
s.m likes this.
eti0123456789 is offline   Reply With Quote

Old   May 18, 2010, 11:00
Default
  #4
Member
 
Moritz Wied
Join Date: Mar 2010
Location: suttgart, germany
Posts: 35
Rep Power: 6
Mo-ITB is on a distinguished road
hi eti,
thanks for your idea, i tried it and it really split my layers. but is it possible that we just run over the internal quality check of snappy?
if i run checkMesh after the layer refinement, it gives me some skew errors...
this is the same as when i use a mesh made by star-ccm+ and convert it to openfoam. it looks nice but does not pass the quality check.

eti, could you tell me which low-reynolds-model you use? i use LamBremhorst, but i have problems with high velocity on some spots, before the laminar layer can build up..
Mo-ITB is offline   Reply With Quote

Old   May 18, 2010, 13:05
Default
  #5
New Member
 
Etienne T.
Join Date: Feb 2010
Posts: 3
Rep Power: 6
eti0123456789 is on a distinguished road
Hello,

I had also this problem of mesh quality, and to avoid that, the only solution I have found is to get the mesh refined near the surface and to reduce the number of "cuttings" with refineWallLayer so that the cells look better. There is also another thing which has effects, but I don't understand why : when I put the parameter "nSmoothThickness" to 0 in the SHMDict, the mesh is more likely to pass checkMesh.

For the turbulence model, up to now I have only used a k-omega SST model, and it seems to work well.
JR22 likes this.
eti0123456789 is offline   Reply With Quote

Old   April 9, 2013, 02:36
Default
  #6
s.m
Senior Member
 
saeideh mohamadi
Join Date: Aug 2012
Posts: 229
Rep Power: 4
s.m is on a distinguished road
hi eti,
would you please explain your text?
e.g. where should we add this text?
thank you very much.
s.m is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
SnappyHexMesh with local refinement of ONE STLfile wolle1982 OpenFOAM Mesh Utilities 16 August 23, 2013 12:12
Boundary layers in Gambit Ian FLUENT 3 March 3, 2012 09:54
snappyHexMesh layers part marine OpenFOAM 7 April 27, 2010 07:09
stitchMesh and snappyHexMesh gdbaldw OpenFOAM 0 December 23, 2009 02:09
no boundary layers using snappyHexMesh thorsten OpenFOAM Native Meshers: snappyHexMesh and Others 1 October 22, 2009 06:01


All times are GMT -4. The time now is 22:49.