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-   -   [ICEM] unstructured 2d airfoil mesh (http://www.cfd-online.com/Forums/ansys-meshing/111623-unstructured-2d-airfoil-mesh.html)

Mazur January 11, 2013 06:58

unstructured 2d airfoil mesh
 
1 Attachment(s)
Hello to every one in my first post. Please forgive me any language erros, because english is not my native language.

Im making some simulations of 2d airfoils in fluent and I make my mesh in icem cfd. I'm familiar with hexa meshing and bloking tehnique, but I want to make a comparison between hexa mesh and mesh made automaticaly. I also will make some more elements airfoils and it propably will be hard for a beginer to properly block the geometry.

I have a big problem with the prism layer over an airfoil. Although the height and the number of prism layers are correct, I am not able to set the element width. Thats a big problem, because the airfoil in mesh does not properly represent the curve contours. I post a picture of the situation.

My second question is how to properly make a mesh in trailing edge of airfoil with higher density. "create mesh density" seems to not function at all.

The parameters I use to mesh is surface patch dependent, quad dominant. I also have checked the "prism" option in part mesh set up. I tried to steere curve mesh params, but it also does not make any change. What do I make wrong?
Thank for all your answers :)

cfd seeker January 11, 2013 07:44

Do you have two curves representing upper and lower sides of the airfoil in your geometry?

If yes first set appropriate no. on nodes on the curves of the airfoil, then create the surface mesh using "All tri", dont use hexa-dominant.

Density box does not work in 2d. Set enough nodes in the trailing edge portion in order to allow prisms to properly fallow the curvature.
Hope it helps you

Mazur January 12, 2013 15:57

4 Attachment(s)
@CFD SEEKER

Thank you for the answer.
Yes I do have two curves representing the airfoil shape, but it does not work properly. The mesher doesn't correspond to the curve parameters I am seting. First when I make a surface 2d mesh i get no inflation layer over my wing at all (although I have it set). Then first when I go to curve mesh parameters I have to choose curve called tmp00 (I suppose it is automaticaly made by mesher) and then when I set parameters for curve tmp00 the mesher is according to my settings. But the curve tmp00 is one, representing the whole airfoil, and then I get those problems I showed in previous post. What is my mistake? Why the mesher does not keep to my curve parameters and generates new curves instead? I'm sittting on that problem for couple days now and I am not able to solve it...
Thanks for every reply!

PS.
I paste two screen shots of the situation. As you see the inflation layer is according to the gray curve which is the "tmp00" the green curve is airfoil and it doesn't work. I also added an additional curve at the trailing edge to dense the mesh but it isn't respected by the mesher at all.

PS2.

I also paste my meshing settings, maybe there I have something wrong?
I will also describe how I make my geometry (maybe there I'm doing a mistake?)

1. Import formated point data (two curves)
2. Drawing the far field. Three straight curves and one circle
3. Making FLUID surface "simpe surface" by selecting curves from previous point.
4. "segment/trim surface" FLUID, by the two airfoil curves.
5. deleting the new surface from point 4. And that's all.

Can You point out any mistake?
Thank for every reply I'm getting desperated ;)

Mazur January 15, 2013 17:09

Please is there anyone who could help me?

BrolY January 16, 2013 04:38

I quickly read your post, and, correct me if I'm wrong, you added curves to your geometry and the mesher didn't follow the mesh options you specified on those curves ?
If you use patch dependent, that's normal. From my experience, patch dependent works only after you did a build topology and use only the curves created by the build topology.
If you want to add curves, you must split your surfaces with those curves, and redo a build topology. The new curves should be created at the junction of two surfaces.

Mazur January 16, 2013 05:44

BrolY thank you for the answer!
"I quickly read your post, and, correct me if I'm wrong, you added curves to your geometry and the mesher didn't follow the mesh options you specified on those curves ?"

exactly :)

"If you use patch dependent, that's normal. From my experience, patch dependent works only after you did a build topology and use only the curves created by the build topology.
If you want to add curves, you must split your surfaces with those curves, and redo a build topology. The new curves should be created at the junction of two surfaces."

Whta does build topology mean? Is it the tmp00 curve that creates it self like i showed in my previous post?
By splitting surfaces you mean situation like if I had an airfoil at 0 degree AoA, and than split the fluid domain in half through the airfoil? I will try to do it that way, but I'm not sure if I understood it right. I would be very thankfull if you explained it to me a bit more speciffied. :)
Thanks for the answer again! I'm stucked with my project because of that problem.

BrolY January 16, 2013 06:21

Build topology recreates the topology of your geometry. For example, depending on the tolerance you specified, it creates the curves between surfaces. Have a look at the user manual, and try to play with it to learn how it works. At the end, you will know if your curves are connected to 1, 2 or more surfaces thanks to a color system (again, have a look at the user manual).
The patch dependent mesher works based on those curves. So if you add curves by your own which are not connected to any surface, the mesher would not take them into account.

"By splitting surfaces you mean situation like if I had an airfoil at 0 degree AoA, and than split the fluid domain in half through the airfoil? I will try to do it that way, but I'm not sure if I understood it right. I would be very thankfull if you explained it to me a bit more speciffied."
I didn't really understand what you mean, but from the picture you provided, if you want your mesh to follow a curve, you need to split the surface with this curve. So the build topology will see 2 surfaces and then, will create a curve between those 2 surfaces. The patch dependent mesher will then "follow" (or respect) the parameter you have specified on this curve.
Do I make myself clear or do you need more explanation ? It's not very easy to explain without being in front of ICEM :S

Mazur January 16, 2013 09:08

3 Attachment(s)
OK so now I'm understanding the idea of build topology.

Now I'm using those curves that create when I'm splitting the FLUID surface. And I get an inflation layer. But still I'm not able to split that curve into two curves. When I do it with geometric options I don't get mesh at all. And the inflation layer doesn't look good in the tail of the airfoil. And also the tetra elements sorrounding the tail of airfoil are in my opinion way to big. I post a picture that shows how does it look like. Can I make it somehow better?

Also about controling the tetra growth from the airfoil (over the inflation layer). I did it by making a rectangular shape and by splitting the FLUID surface into two parts, and then by setting parameters to the surface (max elem size). Is there any other way to make the mesh more densy around the airfoil? Because then in fluent i get parts like "fluid shadow" and I think they are messing with my results. Because although i get nice convergence my results are fully wrong.
Thanks for every answer because I'm getting confused..

Maybe one more question? How acurate can the tetra mesh + inflation layer be? Because with an structured mesh i got accuracy about 5% to air tunnel results(Cl), and this highly satisfying for me. But what about tetra?

BrolY January 16, 2013 09:23

There is an option "density box" which can help you to refine your mesh.
But I think it doesn't work with delaunay volume mesh, only with octree volume mesh .. I'm not sure about it. You should try it (under Mesh -> Create Mesh Density).

Otherwise you could use tetrawidth on the curve you have created ?

Mazur January 16, 2013 09:43

Density box does not work with 2d mesh. And the method I use to make the mesh more densy is rather wrong, beceuse as i said before i get some werid lines like "fluid:shadow". I turn it into "interior" in fluent, but the results are messed up.

BrolY January 16, 2013 09:49

Oh it's a 2D model .. I've never worked with 2D model.

You could split your domain in different surfaces and specify the max size elements on each surface/curve. Is that what you have already done ?

I don't know why it would not work with fluent, but I think the problem "fluid:shadow" comes from Fluent, not from ICEM. I would say it could come from the definition of your BC.

samiyare September 21, 2013 02:18

a Problem with boundary mesh
 
Dear Sirs,
I try to employ your comments. the mesh which created at the trailing edge doesn't follow the curved. I attach a picture of the airfoil. what is the wrong with my case?
thanks.

http://i39.tinypic.com/2zicxhi.jpg
http://i44.tinypic.com/2zf90fl.jpg

Far September 21, 2013 12:33

extend trailing edge

samiyare September 22, 2013 01:26

Links doesnt work
 
Dear sir,
I cannot download the file. maybe the link is broken. would you send me another link or send via email.
my email: habibimeisam@gmail.com
thanks for your attention in advance

Far September 22, 2013 01:58

which file ...

samiyare September 22, 2013 05:48

File
 
Tutorial on 2d hybrid meshing in ICEM





http://goo.gl/JmeCa
http://goo.gl/bacss

Far September 22, 2013 12:21

https://www.dropbox.com/s/oz1hgl9ee0..._2dairfoil.rar

Drop box has blocked by public links for second time. :confused:

metu_aee June 15, 2014 18:29

I generally make my mesh in ansys mesh. Often I cut the trailing edge in design modeler about 3mm from most aft. Thus inflation layer can turn around the aifroil easily. However the results can not be exact since the reflex and camber are lost at the trailing edge even if it is very small.

dengemunzur July 10, 2014 08:15

Unstructured Mesh Around airfoil
 
Dear All,

I have some problems about 2-D unstructured mesh around an airfoil. For my case, I need to obtain mesh arounda an airfoil. I am not experienced with triangular mesh.

And I have some basic problems.

When I tried to obtain mesh, I encountered a problem: I tried to obtain quad layers around the airfoil. When I tried to use the curves that I created, I couldn't have mesh as I wanted; no quad layer around the mesh. However, I obtained the quad layers when I used the curves named as tmp00, etc. I could obtain the quad layers. These were the curves that I had while segmenting the surface into parts created by the ICEM CFD itself.

Am I doing something wrong? I tried to obtain unstructured mesh for simple geometries and I still have the same problem.

I would like to define the airfoil as pressure side, suction side and trailing edge. The curve created by the ICEM is only one curve.
And also what about the additional curves, do I have to add them which part (pressure, suction, etc curves)? otherwise two different curves will be in the geometry.

Thanks to all


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