CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Community Contributions

[cfMesh] genetation of mesh for very thin airfoil propellers

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

Like Tree1Likes
  • 1 Post By nope

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 16, 2019, 06:20
Default genetation of mesh for very thin airfoil propellers
  #1
Senior Member
 
Kmeti Rao
Join Date: May 2019
Posts: 128
Rep Power: 3
Krao is on a distinguished road
Hi dear cfMesh/foam users,

I am using cfMesh since last two years for my cfd applications, thanks to the great tool. So far I had very good experience with cfMesh. As of now I am generating mesh for a wing of propeller which has a similar airfoil profile throughout as shown in the figure airfoil.png. Due to very thin region near the trailing edge no matter how good my refinements are I am unable to generate a mesh with more than two boundary layers. Also with two BLs I am still having a saw-tooth shaped airfoil profile at the trailing edge. Any attempt to add more boundary layers or making more refinements in the region resulting in poor to worst mesh quality during the checkMesh. It would be very great if anyone using cfMesh share their experience for a similar application/similar problem.

My meshing procedure is as follows,

1) Generate geometry in CAD (.stl)
2) Clean/Simplify the geometry using blender(de-featuring)
3) Generate the bounding box
4) Extract/generate surfaces for surfaceRefinement
5) Extract features using surfaceFeatureEdges and storing it as .vtk which is used for edge refinement
6) cartesianMesh to generate mesh

My meshDict,

Quote:
surfaceFile "dynamic.stl";

maxCellSize 0.027;

localRefinement
{


blade
{
additionalRefinementLevels 4;
refinementThickness 0.03;
//cellSize 0.05;
}

}


objectRefinements
{

cylindrical1
{
type cone;
p0 (0 0 0.06);
p1 (0 0 -0.06);
radius0 0.225;
radius1 0.225;
additionalRefinementLevels 2;
refinementThickness 0.027;
}
box1
{
type box;
lengthX 0.22;
lengthY 0.08;
lengthZ 0.045;
centre (-0.12 0.016 -0.011);
additionalRefinementLevels 4;
refinementThickness 0.00375;
}

}
edgeMeshRefinement
{
edge1
{
edgeFile "edgemesh_featureEdges.vtk"; //tip
additionalRefinementLevels 7;
//cellSize 0.005;
refinementThickness 0.0002;
}
}

surfaceMeshRefinement
{
SR1 //tip
{

surfaceFile "SR1.stl";
additionalRefinementLevels 7;
refinementThickness 0.0009;

}



SR2 //LE
{

surfaceFile "SR2.stl";
additionalRefinementLevels 7;
refinementThickness 0.0009;

}

SR3 //TE
{

surfaceFile "SR3.stl";
additionalRefinementLevels 7;
refinementThickness 0.0009;

}


}

boundaryLayers
{


patchBoundaryLayers
{

"(blade)" //patch name
{
nLayers 2;
thicknessRatio 1.2;
maxFirstLayerThickness 0.001;
allowDiscontinuity 0;

}



}

optimiseLayer 1;

optimisationParameters
{

nSmoothNormals 5;

maxNumIterations 5;

// feature size factor. Reasonable range <0.2, 0.5>
// lower values force thinner layers
featureSizeFactor 0.4;

// shall the normal vectors be recalculated
reCalculateNormals 1;

// relative thickess variation between two hair nSmoothNormals
// lower value produce thinner and more uniform layers
relThicknessTol 0.1;
}

}




renameBoundary
{

newPatchNames
{

"blade"
{
newName blade;
type wall;
}

"(patch0|patch1|patch2)"
{
newName rotor;
type patch;
}

}



}
Thank you in advance
Krao
Krao is offline   Reply With Quote

Old   August 16, 2019, 21:47
Default
  #2
New Member
 
Raul Ciria Aylagas
Join Date: Jan 2018
Location: Madrid, Spain
Posts: 3
Rep Power: 3
RaulCA is on a distinguished road
In those cases i stop the proccess after the edgeExtraction step with the workflowControls entry. If this mesh has not the shape you want at the boundaries, you should change something un your settings. You can try with the enforceGeometry option, although it will probably generate a very bad mesh.
RaulCA is offline   Reply With Quote

Old   August 18, 2019, 06:33
Default
  #3
Senior Member
 
Kmeti Rao
Join Date: May 2019
Posts: 128
Rep Power: 3
Krao is on a distinguished road
Hi RaulCA

Quote:
Originally Posted by RaulCA View Post
In those cases i stop the proccess after the edgeExtraction step with the workflowControls entry. If this mesh has not the shape you want at the boundaries, you should change something un your settings. You can try with the enforceGeometry option, although it will probably generate a very bad mesh.
Thank you for your reply. As you have mentioned enforcing geometric constraint has resulted in poor geometry. As you have mentioned about edge extraction step. If it is less refinement I end up with sawtooth edge. With more refinement I'm getting more number of skewness and bad cells. I am facing this problem so long for the first time due to very thin edge.

Krao
Krao is offline   Reply With Quote

Old   August 19, 2019, 06:04
Default
  #4
New Member
 
Join Date: Nov 2017
Posts: 7
Rep Power: 4
nope is on a distinguished road
Hi Kroa

Is the thin edge perfectly sharp? If so, consider to make it blunt. This is easier to mesh and in reality a perfectly sharp thin edge doesn't exist.

This does not really solve your problem, sorry about that. But it might be a way to get around the problem.

Cheers, nope
Krao likes this.
nope is offline   Reply With Quote

Old   August 19, 2019, 06:50
Default
  #5
Senior Member
 
Kmeti Rao
Join Date: May 2019
Posts: 128
Rep Power: 3
Krao is on a distinguished road
Quote:
Originally Posted by nope View Post
Hi Kroa

Is the thin edge perfectly sharp? If so, consider to make it blunt. This is easier to mesh and in reality a perfectly sharp thin edge doesn't exist.

Cheers, nope
Hi nope,

Yes the thin edge is perfectly sharp. I will consider your inputs, thank you. Maybe taking away a couple of micrometers would solve my problem.

Quote:
Originally Posted by nope View Post

This does not really solve your problem, sorry about that. But it might be a way to get around the problem.

Cheers, nope
True! Engineering is all about approximations and finding the best solution with the given amount of resources. Cheers!

If anyone have any other ideas I'm open to those as well, thank you.

Krao
Krao is offline   Reply With Quote

Old   August 19, 2019, 07:13
Default
  #6
Senior Member
 
Kmeti Rao
Join Date: May 2019
Posts: 128
Rep Power: 3
Krao is on a distinguished road
Maybe this link would be useful for the future readers, page 24 of this thread http://www.arek.pajak.info.pl/wp-con...flow_cadOF.pdf discuss about having blunt trailing edges instead of sharp trailing edges.

Krao
Krao is offline   Reply With Quote

Reply

Tags
airfoil, cfmesh, meshing, propeller, thin airfoil

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[ICEM] unstructured 2d airfoil mesh Mazur ANSYS Meshing & Geometry 19 July 26, 2017 12:24
[snappyHexMesh] No layers in a small gap bobburnquist OpenFOAM Meshing & Mesh Conversion 6 August 26, 2015 10:38
[ICEM] Hybrid Mesh on 2D airfoil Jrmy ANSYS Meshing & Geometry 2 August 14, 2014 16:08
[snappyHexMesh] snappyHexMesh won't work - zeros everywhere! sc298 OpenFOAM Meshing & Mesh Conversion 2 March 27, 2011 22:11
fluent add additional zones for the mesh file SSL FLUENT 2 January 26, 2008 12:55


All times are GMT -4. The time now is 23:18.