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[ICEM] Problems with C-topology for airfoil

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Old   December 15, 2009, 07:56
Default Problems with C-topology for airfoil
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Hi ,all
I am trying to mesh a 2D airfoil with ICEM Hexa which has a sharp trailing edge. I have read many threads about airfoil mesh in the forum, and i decide to use C-grid according a topology example as the below four images show.
(pictures are got from the thread :Airfoil meshing)





I have managed to attain a similar block topology,but there is some wrong with my grid.

as the image in the attachment show, my grid line is not a intigrated C-grid, but divided buy center line. The upper grid line do not connect with the lower grid line respectively, they all get together into a point which is the intersection of the center line and the arc.

so, how can i get the real c-grid?

thanks very much for any suggestion.
Attachment 1768

Attachment 1769

Attachment 1770

(the mesh has been coarsen in order to show the grid line clearly.)
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Old   December 15, 2009, 10:00
Default Blocking correctly associated?
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Hi ringtail,

First of all I am no ICEM expert...

Are you sure your blocking is correctly associated to the geometry?
I mean are you sure the vertices are associated to the correct points and the edges to the correct curves?

You can check this by right clicking on "edges" at the "blocking" in the "model tree" and activate "show association".
Another usefull check might be to activate the "projected edge shape" and disactivate the curves.

Try to check this and let me know if all looks good.

Otherwise can you post a clearer image of the front part of your blocking?
Also one showing the associations and projected edge shape? This migth help me...

Kind regards
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Old   December 15, 2009, 15:05
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you associate edges to point. dissociate it and check orthogonality{it may be very poor}
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Old   December 16, 2009, 10:44
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Quote:
Originally Posted by Anorky View Post
Hi ringtail,

First of all I am no ICEM expert...

Are you sure your blocking is correctly associated to the geometry?
I mean are you sure the vertices are associated to the correct points and the edges to the correct curves?

You can check this by right clicking on "edges" at the "blocking" in the "model tree" and activate "show association".
Another usefull check might be to activate the "projected edge shape" and disactivate the curves.

Try to check this and let me know if all looks good.

Otherwise can you post a clearer image of the front part of your blocking?
Also one showing the associations and projected edge shape? This migth help me...

Kind regards
hi , anorky,thanks for your reply.

asoociation:
screenshot4.PNG
screenshot5.jpg
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Old   December 16, 2009, 11:23
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Hi ringtail,

I think tgrt18 is right, you associate edges to point.
If you remove the associations and then correctly associate edges to curves and vertices to points your problem should be solved.

Good luck, and let me know if it works

Kind regards
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Old   December 16, 2009, 23:53
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hi, anorky and tgrt18.

i dont think there is something wrong with the association. Actually, i do not associate any point to edge. I just associate the whole outside wall curves of domain to the whole outside edges.

And i also associate the four inner edges to airfoil shape curves integrally.

According to your suggestion, i activate the "projected edge shape" and disactivate the curves. The below two images have shown the result.

screenshot6.jpg

screenshot7.PNG

i find that the bottom right egdes is missing.

Is this the real reason for th problem? and how can i correct it?

thanks
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Old   December 17, 2009, 05:40
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Hi ringtail,

Indeed the missing bottom edge migth be (part of) your problem.
Some associations are going wrong there.

Try to disassociate all edges and vertices:
go to blocking>edit assoiciations>disassociate; select all vertices and all edges and press apply.
Then start over again, manually associate the correct vertices to the points, and edges to curves.
blocking>edit assoiciations>associate vertex to point
blocking>edit assoiciations>associate edge ->curve

This should solve your missing lower edge and probably as well your other problem.

Let me know if it works, otherwise I'll have a better look at your problem.

Kind regards
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Old   December 17, 2009, 08:50
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Quote:
Originally Posted by Anorky View Post
Hi ringtail,

Indeed the missing bottom edge migth be (part of) your problem.
Some associations are going wrong there.

Try to disassociate all edges and vertices:
go to blocking>edit assoiciations>disassociate; select all vertices and all edges and press apply.
Then start over again, manually associate the correct vertices to the points, and edges to curves.
blocking>edit assoiciations>associate vertex to point
blocking>edit assoiciations>associate edge ->curve

This should solve your missing lower edge and probably as well your other problem.

Let me know if it works, otherwise I'll have a better look at your problem.

Kind regards
Hi Anorky,
I just disassociate all the edges, and the associate them to curves respectively but not integrally.Then the "projected edge shape" semms good as the blow image show.
(I have disabled the curvse and enabled edges->bunching, projected edge shape, and blocks->IJK. )
Attachment 1809
For describing the problem more clearly, I have uploaded the geometry and block files.
airfoil.zip
Attached Images
File Type: jpg Screenshot.jpg (47.9 KB, 64 views)
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Old   December 17, 2009, 11:26
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Hi ringtail,

I tried blocking your geometry and for me it works.
I uploaded the new geometry and blocking file and the replay file.

I changed your geometry a bit, in order to associate all vertices to points.

I split the blocking 2 times in x and y direction, see 3.blk to see the result.

Then I merged the 2 vertices near the trailing edge together. Do the same at the middle of your outlet plane, the middle block behind the Trailing edge disappears.

Delete the block inside the airfoil

move the vertices near the leading edge of the airfoil to the respective upper and lower points, splitting the airfoil upper and lower curve. (this vertices are the "forward" cornerpoints of the middle blocks in x direction near the airfoil)

Move the vertice at the middle of the inlet towards the leading edge of your airfoil.

merge the most upper and lower vertice at the inlet together and place it at the middle of the curved inlet (I mean the most forward negative x coordinate point of the geometry)


delete the block inside the airfoil

Then associate the remaing vertices to the correct points,
do the same for the edges to curves

set your meshing parasms and this should work.

I'm sorry for the bad, unstructured explaination but for the moment I don't have much time...
Anyway the correct file are 2.tin and 2.blk

This should help you out, if not let me know.

kind regards and good luck
Attached Files
File Type: zip airfoil.zip (20.6 KB, 49 views)
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Old   December 18, 2009, 12:00
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Hi, anorky.
I'm very much obliged to you.
After studing the files your give me, I learned how to divide blocks.
Then, I tried to mesh my original geometry model . Your method also works well. The mesh quality is good.

But, there are some other problems. After i converted the pre-mesh to unstructured mesh, I check it, and ICEM notify there are "single edges" around the airfoil and outside domain walls.

I also tried to convert the mesh to FLUENT v6 format, then check it . FLuent think the mesh is good.
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Old   December 19, 2009, 16:55
Default Single edges is expected on a 2D model.
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Single edges is under "possible problems".

It just means that the elements are not surrounded by other elements. In a 2D model, you should expect single edges around the perimeter. As long as you have line elements around the perimeter for Fluent to hang the boundary conditions on, you will be fine (if you didn't, it would give an uncovered faces check in ICEM CFD or a Null Pointer error in Fluent.)
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Old   December 19, 2009, 23:00
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Quote:
Originally Posted by PSYMN View Post
Single edges is under "possible problems".

It just means that the elements are not surrounded by other elements. In a 2D model, you should expect single edges around the perimeter. As long as you have line elements around the perimeter for Fluent to hang the boundary conditions on, you will be fine (if you didn't, it would give an uncovered faces check in ICEM CFD or a Null Pointer error in Fluent.)
I see , thank you
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