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how to deal with sharp trailing edges in icem

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Old   May 18, 2010, 13:27
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joegi
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Hi,

I used curve settings instead of surface settings because I was using a patch dependent method and then filling the interior with a delaunay method (let me know if this is the correct way).

I will check my periodic settings, but basically the periodic faces were different when visually inspecting ("view => front"). For the grid without the prismatic layers the mesh was perfectly periodic.

Btw, where do you find the option to run the periodic checks?

Joel
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Old   May 18, 2010, 13:51
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Joel,

Oops, there is the part I missed. The Patch Based Mesher does not respect the periodicity settings, at least not by default. To make it happen, you can mesh the one side, lock all the nodes, copy over to the other side and then mesh the remaining surfaces while respecting line elements... Not the easiest way to handle things. In your case, it worked out ok in the beginning (coincidence) because your curve sizes were all periodic.

But yes, if you want to use Patch Conforming mesh, you need to set the curve sizes.

The Check Periodicity option is under Edit Mesh => Check Mesh.
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Old   June 6, 2010, 15:03
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Hi Simon,

Here are where the bad elements are, and blocking.

Thanks,

Brian
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File Type: jpg bad_elements.jpg (84.6 KB, 216 views)
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Old   June 7, 2010, 09:15
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I can't really see these elements in this pic, but I can see that they are the trailing edge wedges, both within the solid and the fluid.

First off, you can ignore the poor quality solid elements unless you are doing conjugate heat transfer. If you do need to keep them, the rest below still applies.

You can improve the quality a little on the far side of the fluid by opening up the angle there. The geometry doesn't go all the way, so the mesh doesn't need to be perfectly conformed to that shape all the way either. Open it up to 30 or 60 degrees at the FF using edge splits (not block splits). But this still won't help the elements right at the trailing edge.

Zoom in and take a look at those. The angle is constrained by the geometry, so you can't do anything about that. But if they are really long and skinny (long in the chord direction short across) then perhaps reducing the side 2 mesh size is the best solution to improve aspect ratio. Also look and make sure they don't appear warped or twisted (usually a mis-projection issue or an issue with misaligned edge params).

If your only concern is angle (which you can't possibly fix due to geometry constraints), then I suggest you just send it to the solver and see if the solver is as concerned about it as you are.

Keep in mind that these are just metrics, and some may not align with the needs of your particular solver. The ICEM CFD Quality metric is very "conservative" for prism quality. To calculate the ICEM CFD Quality metric, the software actually divides the prism (Penta-6) into 3 tetras (numerically speaking) and then gives the quality of the worst one. This very conservative metric is needed for some solvers, but not for others.

If you were checking based on "min angle", you would also get a low number, but that would be because it was a prism... The ideal angle for a Hexa is 90 and you really want to stay above 18 or at least 9 degrees for Fluent, but the ideal angle for a prism is 60, and the min angle tolerated by Fluent is much lower.

At 13.0, we are introducing a new "Orthogonal Quality" metric designed by a team of Fluent and CFX developers as the best measure of quality for those solvers.

Last edited by PSYMN; June 7, 2010 at 09:16. Reason: :0
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Old   June 10, 2010, 22:48
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Hi Simon,

Here is where I am getting angles below 9 degrees. I have tried a few things but no improvement. Any suggestions?

Thanks
Brian
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Old   June 11, 2010, 08:49
Default Ogrid on the inside...
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This is inside your wing... Do you need to keep the mesh inside your wing for conjugate heat transfer?

This is basically the exact same problem as you had on your far field... The fix is the same also.

If you need the mesh inside your wing (and beyond the wing tip), You must extend your CGrid into your wing and then split the ogrid to capture the surface of the wing. Then collapse three trailing edge blocks. If you don't get it, I can show you...

Another option (I forget your exact topology, so this might not apply) is to sweep unstructured mesh thru the inside of the wing... This would prevent your solid mesh count from getting too high and would be fun to do... Look under "Blocking (tab) => Edit Blocks => Change Block Type" Look for sweep and select the triangular face on the one side.

Simon
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Old   June 11, 2010, 22:02
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sorry the pic is decieving, the elements are actually right on the surface of the wing. Ill try a few things over the weekend.

thanks,

Brian
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Old   June 12, 2010, 00:51
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The elements outside the wing shouldn't have any topology related angle issues... Are you sure these are not right inside where the HGrid corners are opened up to the continuous curve on the inside of the airfoil?
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Old   June 14, 2010, 07:02
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Could you show me how to " If you need the mesh inside your wing (and beyond the wing tip), You must extend your CGrid into your wing and then split the ogrid to capture the surface of the wing. Then collapse three trailing edge blocks. If you don't get it, I can show you..." , thanks a lot.
I am still confused about how to mesh beside the wing tip.
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Old   June 14, 2010, 22:30
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Hi Simon,

You were right, the elements were on the inside of the wing. I tried all the suggestions you mentioned but could not get rid of the low angle elements. Fluent seemed to like the mesh engough to try to solve. Now I will see if I can get a reasonably converged solution.

I can see what splitting edges does(at least along a curved line) but couldnt really tell any difference in the mesh??

Thanks

Brian
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Old   May 8, 2014, 09:59
Default Sharp corners of wedges
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hii I am new to Icem want to mesh one of the part of the object below please give me an idea for blocking of that object..
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