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ICEM aircraft mesh trailing edge difficulty

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Old   July 18, 2011, 11:37
Default ICEM aircraft mesh trailing edge difficulty
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Monty Roberts
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I am having a problem with meshing trailing edges. I have tried to associate the mesh with the edge curves. This does not seem to work.

The trailing edge of the root fillet is also a problem.

I'm a newb so feel free to point out any obvious problems, they are probably not obvious to me....

Any tips?
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Old   July 20, 2011, 11:16
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Monty Roberts
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I have improved the trailing edge situation. Mainly by changing the Edge Criterion in Volume Meshing Parameters under the Global Meshing Setup tab.

I also tried using define thin cuts. However, this resulted in a lot of holes in the mesh along the leading edge.

There are other vexing problems now:
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Old   July 22, 2011, 14:39
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After a lot of head scratching, I seem to be getting somewhere.

For those who come here searching for answers in the future I thought I would share what I learned.

1.) Trying to fix a problem like this by lowering the edge criterion will reach a point of diminishing returns. It is far better to construct the geometry so that the mesher "likes" it. I did this by truncating the aft edge of the airfoils. There is a blunt trailing edge about .25 in thick. This allows you to force the mesh to a smaller size along the trailing edge and prevents the small angle problem.

2.) Using thin cuts is also not a very good option.

This is starting to look like something I feel like I can run an analysis on. I still need to increase the fluid mesh density around the nose of the aircraft.......First I need to buy some more RAM
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Old   July 23, 2011, 13:56
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I admire your persistence to try and figure this out. It looks like you were getting close on your own, but like Wile-E-Coyote, it may have been good to combine methods in the right way...

Edge criterion definitely matters, but it may not get you all the way there on its own...

You should also use thin cuts, but they will fail if your trailing edge is not in a different component... So if the top surface is "A" and the bottom is "B", the curve between them can not be in "A" or "B", Put the curve in "C". In fact, if those two parts touch anywhere in the model, the thin cut will fail and you will see a message about it scroll by in the message window. This has to do with the logic of the thin cut algorithm and you can read more about it in the help.

Instead of creating a small flat edge to put a size on, you can just apply a finer size to the trailing edge curve its self...

You could also create a density line by picking points along the trailing edge... (this can be used to set the max size in this critical area).
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Old   July 23, 2011, 21:46
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PSYMN,

Thanks for the tips. I will try the edge curve trick. I could not get it to work because (as you accurately surmised)...I had it in the same part.

I was being lazy by modeling the surfaces that way, the flat trailing edge is more accurate.

I have done some structural analysis, but not much CFD...I'm learning as I go. Thin edges and points where geometry all comes together are my long term nemesis...in the modeling world, as well.

Unfortunately, I had everything ready to load into fluent, only to discover that our license only supports 500K cells...I have closer to 5 million, before refinement and using symmetry. Our license also does not support parallel processing.

This isn't commercial, and is only me trying to learn the ropes while working on an interesting problem.

Seems I'll be looking into OpenFoam......
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