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Meshing an airfoil (3D - OF 2.2.0)

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Old   April 16, 2013, 09:47
Default Meshing an airfoil (3D - OF 2.2.0)
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Andreas Wendy
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Hi everybody,

currently I am trying to get a nice mesh of two rotor blades in an three-dimensional mesh.
But the mesh I get is not satisfying. The trailing edge is everything else then sharp and on the top and the bottom of the profile I get some "buckles".
I need a spherical mesh so my procedure is the following.

1. blockMesh
2. snappyHexmesh to get a spherical Mesh and refine the region around the airfoil
3. Meshing the airfoil with snappyHexMesh

You can find the case in the following url: http://ubuntuone.com/2Q0ITgnwbAr7zfvGonRAUe


I use for meshing OpenFOAM 2.2.0


I also have a different question. Is it possible to get on each patch (m1... - m9, p1... - p9...) different thicknesses of the first boundary layer?
I need them for getting good values for y+.

Best wishes

Andreas
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Old   April 18, 2013, 05:24
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Timo Kulju
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For the edges, try using surfaceFeatureExtract-utility (see $FOAM_TUTORIALS/mesh/snappyHexMesh/flange/ ). In my experience, for good mesh the blockMesh should be formed with perfect cubes. But I'm not 100% sure about that... For the layers, I think the number of layer levels can be defined per patch.

Best,

- Timo
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Old   July 9, 2013, 05:25
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Artur
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Hi,

I've been having similar issues as you when meshing a marine propeller.

I've discovered that with a "nice" .stl file with a smooth, continuous edge the surfaceFeatureExtract utility will not capture it unless you set (in the dict file):

minElem 1;

(In most tutorial cases I've seen it's set to a value between 5 or 10 by default) You can then see what edges have been extracted by running:

surfaceFeatureConvert constant/triSurface/your_file.eMesh your_file.obj

and then simply viewing it in paraview and comparing against the original .stl or the mesh.

Hope this helps.

Cheers,

Artur

P.S. I've been trying to find a way of having different layer mesh settings too but haven't found anything yet except for having different no. layers as pointed out by Timo. Let me know if you find out more about this please.
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Old   July 13, 2013, 07:08
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Miro
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Hi there,

you should run surfaceFeatureExtract. Then you can check what it did by:

Code:
surfaceFeatureConvert constant/triSurface/your_file_name.eMesh your_file_name.obj
paraview your_file_name.obj
change the angle in surfaceFeatureExtract dictionary and see what happens.

then you can reduce ResolveFeatureAngle in snappyHexMeshDict.

you can also use implicit feature snap. (disable the explicit)

I hope it helps. It should work. I'm also meshing a wing in snappy, but can't add boundary layer, everything else works fine.
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Old   August 19, 2013, 09:12
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saeideh mohamadi
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Quote:
Originally Posted by miro2000 View Post
Hi there,

you should run surfaceFeatureExtract. Then you can check what it did by:

Code:
surfaceFeatureConvert constant/triSurface/your_file_name.eMesh your_file_name.obj
paraview your_file_name.obj
change the angle in surfaceFeatureExtract dictionary and see what happens.

then you can reduce ResolveFeatureAngle in snappyHexMeshDict.

you can also use implicit feature snap. (disable the explicit)

I hope it helps. It should work. I'm also meshing a wing in snappy, but can't add boundary layer, everything else works fine.
Dear Miro,
what is the difference between implicit feature snap and explicit one?
i ask this question because you suggest for disabaling the explicit feature snap, and i don't why?
Thanks
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Old   August 19, 2013, 11:57
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Quote:
Originally Posted by s.m View Post
Dear Miro,
what is the difference between implicit feature snap and explicit one?
i ask this question because you suggest for disabaling the explicit feature snap, and i don't why?
Thanks
Dear s.m., thank you for your intrest;

this post was made in moments i was just learning ways with snappy, so I don't use implicit f.s. anymore.

As far as I know, you can have implicit, explicit or none f.s.
I'm not sure, but I think that implicit doesn't use the e-mesh files for snapping, but makes it's own on-the-fly.
Explicit, on the other hand, lets you define angle below your .stl mesh (or features) will be picked-up.
Someone should correct me if this is not true.

Note that you don't need to use explicit feature snapping for refinement only, if your surface is not smooth somewhere, running e.f.s. on that place with the same refinement as the surface could fix the problem.

Please ask if you have further questions
- miro
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Old   October 12, 2013, 08:01
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saeideh mohamadi
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Quote:
Originally Posted by Artur View Post
Hi,

I've been having similar issues as you when meshing a marine propeller.

I've discovered that with a "nice" .stl file with a smooth, continuous edge the surfaceFeatureExtract utility will not capture it unless you set (in the dict file):

minElem 1;

(In most tutorial cases I've seen it's set to a value between 5 or 10 by default) You can then see what edges have been extracted by running:

surfaceFeatureConvert constant/triSurface/your_file.eMesh your_file.obj

and then simply viewing it in paraview and comparing against the original .stl or the mesh.

Hope this helps.

Cheers,

Artur

P.S. I've been trying to find a way of having different layer mesh settings too but haven't found anything yet except for having different no. layers as pointed out by Timo. Let me know if you find out more about this please.
Dear artur,
i didn't understand where we should set "minElem 1;" to have a beeter *.eMesh after runnig the surfaceFeatureExtract?
whould you please guide me,
Thank you very much.
P.S. i have three stl file, i put my surfaceFeatureExtractDict in the attachment.
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File Type: txt surfaceFeatureExtractDict.txt (2.3 KB, 10 views)
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Old   October 12, 2013, 13:07
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Try this:

Code:
propeller.stl
{
	// How to obtain raw features (extractFromFile || extractFromSurface)
	extractionMethod    extractFromSurface;

	extractFromSurfaceCoeffs
	{
	    // Mark edges whose adjacent surface normals are at an angle less
	    // than includedAngle as features
	    // - 0  : selects no edges
	    // - 180: selects all edges
	    includedAngle   160;
	}

	trimFeatures
	{
	    // Remove features with fewer than the specified number of edges
	    minElem         1;
	}
}
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