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2D hybrid grid around high-lift airfoil

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Old   October 14, 2011, 11:22
Default 2D hybrid grid around high-lift airfoil
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Bastian Nebenfuehr
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Hello everyone,

I'm trying to create a grid around a three-element high-lift airfoil. In principle, I would like to have an unstructured grid, but with some structured regions in it. For example, I want to resolve the boundary layers with a structured approach and maybe some smaller regions between the elements. So, I admit that this is not entirely a new problem here. I think I would have to take a similar approach as done already in this thread here:
Hybrid mesh for 2D boundary layer

What I have tried, is the following:

1) I define a lot of small surfaces in the entire domain, on which I put a "2D surface blocking". Then I specify the respective surfaces to be either "mapped" or "free" with "all quads" or "all tets". This works, but seems very cumbersome, not to mention that the grid quality is rather bad.

2) I also tried using a "2D planar" blocking from the beginning and using O-grids around my airfoil-elements. This works great for the boundary layers, but I did not manage to specify some blcoks being structured and others unstructured.

So, I think an intermediate approach would be ideal, but I did not manage to combine a "2D surface blcoking" with a "2D planar". It seems like they cannot coexist, if I chose one of them, the other one disappears.

What would be your recommendations or what is the approach to pursue?

Any comments will be greatly appreciated!

/Bastian

Ps: Unfortunately, I cannot post a picture of my geometry here, but just to get an idea, of what kind of thing I'm talking about, look here:
http://people.nas.nasa.gov/~rogers/pegasus/images/fig1.jpg
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Old   October 15, 2011, 09:48
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Simon Pereira
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I would use 2D Planar and split the blocks to get what you need... Have you seen the Youtube video (yours would need extra splits to separate out the flaps and slats and then you would only delete the blocks in the solid regions...) This is the link to part one of three...

http://www.youtube.com/ansysinc#p/u/37/tYrbScUH9RE

If you already have the geometry, you can skip the geometry creation portion...

Once the model is blocked out, you could convert far field blocks to unstructured triangles if you like...
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Old   October 27, 2011, 02:59
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Bastian Nebenfuehr
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Hi,

thanks for the reply. I still have not yet found the time to test this properly, but I remember last time I tried, I had trouble converting the blocks into unstructured blocks. Even though I convert the blocks into "free" blocks, I still got "quad" elements. What is the trick to get only "tri" elements?
For the rest, I knew the video, but thanks anyhow, it's extremely helpful!

Best,
Bastian.
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Old   October 28, 2011, 07:13
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Bastian Nebenfuehr
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Now I made a test with a 2D planar blocking around my airfoil. It works quite nicely, but I still am not able to create blocks that are only producing tets. How do I do that?

Thanks,
Bastian.
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Old   October 28, 2011, 10:41
Default Free Face Mesh Type
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After making a block "free", the mesh defaults to quad with (up to) 1 tri.

You need to go in and set the "Free Face Mesh Type" to "All Tri" if that is the sort of paving that you want...

FreeFaceMeshType.jpg
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Old   October 28, 2011, 10:43
Default Quad Dominant
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You may actually prefer to go with quad dominant...

FreeFaceMeshType_QuadDominant.jpg
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Old   October 30, 2011, 07:22
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Bastian Nebenfuehr
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Thanks again. Now I was able to create a mesh in the way that I wanted. It only needs a little (well, actually a lot) of fine tuning.
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