Blade tip blocking (icem)
 

Hi everybody,

I'm meshing a three blade wind turbine and some blocking located at the blade tip are causing me trouble.
In the 1st picture you can see the blade tip with sharp trailing edge and its blocking. There are O-grid blocks around the blade and then all edges converge to a unique vertex in the very extreme of the tip + O-grid distance (vertex 624).
In the message box you can see that a collapsed edge is causing an internal error. This is causing negatives volumes as it is shown in the histogram (negative volumes for the same point of view are shown in the 2nd picture).

How can I avoid that?

Is there a better option for blocking at the blade tip?

Thanks in advance!

attach files.

that's not what I would call a sharp trailing edge...

In the picture the visible edge is the leading edge. The trailing one is on the backward side.
Also, it can be confusing because there's a curve of the same colour as the surface.
But I think that's a sharp edge.

Thanks.

Well, geometry files are not mine so I can't share them until I got permission. :D

I've realized that negative volumes are not only at the blade tip but in the whole blade surface. I'm gonna try a simpler blocking around the blade and I'll try again.

I'll keep posting.

Like this? :cool:


http://imageshack.us/a/img822/7977/sharpwing005.jpg

http://imageshack.us/a/img856/7364/sharpwing006.jpg

http://imageshack.us/a/img51/5707/sharpwing001.jpg

http://imageshack.us/a/img819/5300/sharpwing004.jpg


http://imageshack.us/a/img203/8971/sharpwing002.jpg

http://imageshack.us/a/img546/2905/sharpwing003.jpg

PS: This was not done by me. I guess this master piece was done by Ralen (But I am not sure)

see this post

http://www.cfd-online.com/Forums/ans...ca0009-3d.html

For 2nd thought

http://www.cfd-online.com/Forums/ans...spinnaker.html

Hi, I'm back with the blade tip blocking after some days off. I've seen Ralen's approach but I have some questions. In the comment #12 of the thread:

http://www.cfd-online.com/Forums/ans...tml#post362126

In step 2 and 3 I don't know exactly in which surface I have to do the o-grid. I guess it's in the selected surfaces in the attached picture, if I am right how do I create an outer o-grid in just that selected surfaces? If I enable around selected blocks the o-grid appears all around the blocks, and not just in the selected surfaces.

I've already solved that, I was just messed up with the o-grid selection. :D

After several trials I've managed to get some valid blocking for the blade tip following Ralen's approach. See picture 1 before associating vertices :cool:
Then I've made all the vertex-point, edge-curve and face-surface associations (picture 2 and 3).
But when I start meshing, there's somethins strange at the tip (see pictures 4 and 5), this has happened to me other times but I don't know how to fix it now. I've checked all associations and they seem all right to me. Why does this happen?:confused:

Solved, I just had to move one of the vertex because it was to close to side1 instead of side2.

good...................

I've found a new issue. I've been trying to solve it for a while but I can't find a solution.
The problem is that I want to mesh two parallel edges from a rectangular surface, everything pretty simple (purple surface in picture 1). I've done the associations point-vertex, edge-curve and face-surface. I do the bunching (picture 2), copying to all parallel edges, but it's not meshing properly (picture 3). The two long parallel edges are being mesh just from a concentrated point near the corners (pictures 4 y 5).

What is the cause? What can be the solution?

Thanks a lot!

PS: I don't know if I should open a new thread for this matter, as it is no longer related to the balade tip.

It is the association issue. check associations !

I've checked all associations, even edge to surface ones (picture 1). Everything seem okay. I've done the same for the nearby rectangle and this one has been properly meshed (picture 2).

You think it's a edge to curve association issue of the two long sides?

Yes. It could be edge to curve or vertex to point association problem.

I still don't find the problem. What does the white arrows in previous picture 1 mean? I don't hace those arrows in the other rectangles.

Blocking -> Associate -> Update Association.

If it doesn't work, you would have to redo all the association hand by hand.
Your problem sometimes occures if you delete curves or trim surfaces ... It's always better to disassociate a curve (Blocking -> Associate -> Disassociate from geometry -> Edges), and then reassociate.

Good luck ;)

That solved the problem! Far, you're the man.

I meant Alenxadre, merci beaucoup! Thank you too, Far!

That was Broly not FAR !!!:p

Yes he is not Far from you

Volume orientations
 

Well, returning to the initial topic of this thread, some days ago I got negative volumes due to bad quality elements, I though it was just on the blade tip but it resulted to be all over the blade surface.

I've done all the blocking again to make it simpler, I've moved vertices to avoid complicated shapes, etc. but I still get many negative volumes (pictures 1 and 2).

I've tried the block check options: run-check/fix and fix inverted blocks and nothing changed.:(

I choose to fix them
Then a message appears about multiple edge (picture 3) and I choose to ignore.:confused:

Then another message appears about non-manifold edges (picture 4) and I choose to fix (441 out of 2644 could not be fixed).:(
And that's it.

How can I improve those 208 elements quality to avoid the volume orientation issue? as I guess volume orientation is the cause of negative volumes.


What should I try next? Any ideas?

That looks like to be an association issue. But you should share your .tin and .blk file so we could have a look.

For your record, multiple edge is a possible problem.
But if you have 3 or more surfaces which intersect at the same curve, this curve would be considered as a multiple edge. So that's not a problem.
But if you have 2 surfaces which intersect at the same curve, this curve should NOT be considered as a multiple edge, otherwise, there is a problem.

Non manifold vertices often means nodes which are not connected to other nodes ..

Geometry is not mine, so I'm not allowed to share it now.:(

I don't have 3 or more surfaces intersecting in a curve.

I have many pairs of surfaces intersecting in the same curve. How can I know that these curves are multiple edges? How can I change them to single edge?

Merci bien pour l'aide!

On the tree menu, right click on curve -> color by count :

Yellow means that the curve is in contact with one surface.
Red means that the curve is in contact with 2 surfaces.
Blue means that the curve is in contact with 3 or more surfaces.

That colors means something if you have done a build topology. Otherwise, all your curves would be colored by yellow.

Are you sure you have associated all your edge with the right curve ?
Zoom more around the blade, make picture with the mesh.
Do the same without, only with curve and with the option "show association" activated.

Here you are some pics:

It's really hard to help you without the project files ..

I know, I'm sorry. I'm gonna ask if I can upload the files but that won't be until tomorrow. I'll keep posting.

Thanks a lot.

That is wind turbine ?

Yes, it's a wind turbine, a 120º sector with periodic boundary conditions to use a rotating SRF in Fluent.

Curves colored by count
 

You can see the counts by color in the pics. I have blue, red, green and yellow curves in the sector and prism around the blade. And green and yellow coincident curves in the blade. What does green mean?

What is to build a topology? I've created geometry and blocking for the prism around the blade, and then imported a sub-topology for the rest of the domain.

I've found many extra curves, I guess I have to delete them and leave just one curve, and then associate that only curve to each edge. Right?

I'm very sorry I cannot upload geometry and blocking files.

Thanks a lot for your effort guys!

How do you import the sub-topo? How does sub-topo work and what is the advantage of using it?

I started working just with the prism around the blade, to make it easier to remesh as it is a smaller domain. I did the rest of the domain in another project, so when I wanted to merged both blocking files I had to use sub topologies.
On the tree menu, on topologies, right click and save, it is saved as a blocking file. Then in the other project I had to import that file.

I asked for info about that in this thread: http://www.cfd-online.com/Forums/ans...tml#post408760

What is difference between making a single blocking and using suptopo? How do you make sure that at interface you have similar features for both blocking files?

I'm not sure about that, I just wanted to find a way to import some blocks into a file with many blocks. I think I have to apply the merge option to get just one blocking.

Unattached, single and double edges
 

I've been cleaning the geometry, deleting all redundant curves and points, and making some reading from icem help manual, and I've realized that I have many unattached curves even if it's supposed to be a two surfaces intersection, is that a problem?
The same happens with single and double edges. There are just two multiple edges (blue).

I attach some pictures of unattached (green, picture 1), single (yellow, picture 2) and double curves (red, picture 3), a general view of surfaces (picture 3) and a picture with surfaces in grey scale where you can see the double and multiple curves (picture 5).

The domain is a 120º cylinder sector with inlet, outlet, two symmetry curved faces and two flat periodic faces. Then there's a prism around the blade with several surfaces.

Please, ask me any required info. Thank you very much!

Already asked by Broly ;)


This topic has been discussed in very much detail by Simon. Search on forum.

Negative volumes in a simpler case
 

Well, I've found that same problem in a way more simple case. It's a 3D flat plate inside a prismatic domain. Even if blocking is very simple, after specifying the bunching in all edges (I don't use to specify surface mesh parameters, are they really necessary?) and pre-meshing, many tiny negative volumes appear (see picture), of the order of 7e-13 and smaller (see histogram in the picture)

I guess this issue has something to do with the blade one, so I'd really appreciate any help, as I'm running out of time...:(

As it is hard to be helped without .prj .tin nor .blk files I upload them so it's easier to be helped.

Thanks you all, guys!

Well, I've managed to resolved the issue in this simpler case. It was just reducing the bunching in some edges and negative volumes dissappeared.

So my questions are:
How can bunching generate negative volumes?
If an edge has too much nodes it seems to end up in negative volumes. Isn't it a limitation of the size of the mesh?

Thanks