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[ICEM] Shifted Periodic topology

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Old   August 14, 2013, 07:20
Default Shifted Periodic topology
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Hi,
I want to mesh a 2D propeller blade with shifted periodic topology. I have seen some post where Simon was discussing about Shifted periodic topology. He has shown some example where he has applied Shifted periodic topology to wind turbine. I understood to certain extent but I don't know how to apply shifted periodic topology to my 2D propeller blade.

I have already meshed my geometry using O and C grid topologies. Firstly I created a block and made it periodic. Then I made a two horizontal split (along y-axis), one in the front of the blade and other behind the blade. And I also made two vertical split (along x-axis), one in the suction side and other in the pressure side. Then I inserted a O-block and merged the vertex in the trailing edge and converted into C-block. Then I associated the edges to the curves of the airfoil. The blocking strategy with C-Grid is shown in image 1 and the mesh is shown in the image 2. This blocking strategy works fine. But for highly stagger blade I heard it is better to with
shifted periodic topology.

As my geometry is periodic and it have as a different periodic boundary shape, I don't know how to create the shifted periodic topology. Actually I am trying to mesh a 3D propeller blade. Before going to 3D mesh. I think it is better if I master the meshing of 2D propeller geometry.

The details of 3D propeller geometry is discussed in the below thread

Propeller blade-Shifted periodic or J-Type BLOCK


Here is the link for the tin and blocking file
http://www.4shared.com/file/7WEA7lbg/Front_rotor.html
http://www.4shared.com/file/ekJacT6x/Front_rotor.html
http://www.4shared.com/file/KnzTI61V/Front_rotor.html

Please help me. Thanks in advance for your guidelines.
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Old   August 15, 2013, 08:35
Default Shifted Periodic topology
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Hi,
In the last post i forgot the attach the images. You can see the images in this post.
Attached Images
File Type: jpg blocking (1).jpg (42.6 KB, 35 views)
File Type: jpg mesh.jpg (85.5 KB, 32 views)
File Type: jpg ShiftedPeriodic.jpg (2.5 KB, 103 views)
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Old   August 15, 2013, 10:03
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It is done by adding a split to each side (adds two extra indices) and then collapsing all but one of the blocks in the new columns... (under merge verticies) The block you dont collapse (one on each side) is what gives you the final extra index...

Then go in and setup your periodic verticies to be shifted...
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Old   August 16, 2013, 07:13
Default Shifted Periodic topology
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Simon, thanks for your suggestion. I gave an attempt to create shifted periodic topology.

Quote:
It is done by adding a split to each side (adds two extra indices)
Simon, I don't understand which split you are talking about. Is it the split made for creating quater O grid (Image 2 and 3)?

Quote:
then collapsing all but one of the blocks in the new columns... (under merge verticies)
Do you mean that I want to collapse the block just behind the trailling edge to creat a C-grid (as sown in the image 1 of the next post)

Quote:
The block you dont collapse (one on each side) is what gives you the final extra index...
I dont get this point. Could you please explain a bit more.


I followed the blocking strategy as shown in the image 1. Firstly, I created a 2D planar block. Then I made a vertical and horizontal split ash shown in the Image 2. Then I created a quarter O grid by by choosing the appropriate block and edges (Image 2). Again I created another quarter O grid behind the trailing edge of the airfoil (Image 3). Image 4 depicts the two quarter O grid, one in the front and other in the behind the airfoil.

And I made three splits as in the image 5. Then I made the vertex periodic and associated the edges to curve. I deleted the block (1) which corresponds to the airfoil. Then I collapsed the block 2, 3, 4 (Image 1 - in the next post). Then I aligned the vertex and got a blocking as shown in image 2 - in the next post.

Still I am not able to get a good quality mesh. I have high skew cells as marked in the image 3- in the next post. Simon could you please check the things that I have done. Should I want to change the blocking method. I don't know where I am going wrong.

tin and blk files can be found in the below link

http://www.4shared.com/file/ZhYvmqBk...odic_try1.html
http://www.4shared.com/file/TBnobxP3...odic_try1.html
http://www.4shared.com/file/hUUVwVX8...odic_try1.html
Attached Images
File Type: jpg ShiftedPeriodic.jpg (55.6 KB, 29 views)
File Type: jpg quater o grid1.jpg (86.4 KB, 21 views)
File Type: jpg quater o grid2.jpg (89.7 KB, 18 views)
File Type: jpg quater o grid at LE and TE.jpg (85.2 KB, 17 views)
File Type: jpg split.jpg (87.0 KB, 18 views)
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Old   August 16, 2013, 07:16
Default Shifted Periodic topology
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I am posting the reaming images of the previous post
Attached Images
File Type: jpg collapse edge.jpg (87.6 KB, 24 views)
File Type: jpg Blocking.jpg.jpg (34.1 KB, 20 views)
File Type: jpg Mesh.jpg.jpg.jpg (89.3 KB, 26 views)
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Old   August 16, 2013, 07:39
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Original indices were :

1 (blue) = 1 (red)

2 (blue) 3 (red)

3 (blue) =

4 (blue) = 5 (red)

5 (blue) =6 (red)

6 (blue) =7 (red)

8 (blue) =8 (red)

2 (red) and 7 (blue) are created using the quarter o-grid!!!

PS: I am not able to work on any problem as my laptop is out of order (mother board fault) and will get it on coming monday
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Old   August 16, 2013, 10:10
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Quote:
Originally Posted by venkat_aero2007 View Post

Still I am not able to get a good quality mesh. I have high skew cells as marked in the image 3- in the next post. Simon could you please check the things that I have done. Should I want to change the blocking method. I don't know where I am going wrong.
[URL]http://www.4sha
You shifted it the wrong way... You shifted it so that your mesh had to shift even more in the section... You want to shift it the other way so that the mesh crosses the section more orthogonally, not less...

Put the extra index on the other side...
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Old   August 16, 2013, 10:26
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I think shifted peridoic is just equivalent to creating two to three quarter ogrids!!! Am I correct?
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Old   August 16, 2013, 11:32
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Quote:
Originally Posted by Far View Post
I think shifted periodic is just equivalent to creating two to three quarter ogrids!!! Am I correct?
We call it shifted periodic because we apply the periodic verts to different indicies... For Periodic, the number of verts (indicies) needs to be the same. The quarter ogrid added to one side means that we need to add one to the other side to make things even again. Shifting gives us some angular freedom between the periodic verts... Specifically, it lets us be more orthogonal when the blade is steeply inclined.

You could do it with 2 or 3 (or more) PAIRS of quarter ogrids if you want to shift it more, but you always need a matching pair on the other side for periodicity.

If you want to forget about periodicity (non conformal periodic), then you don't need to worry about shifting things at all.
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Old   August 21, 2013, 09:31
Default Shifted Periodic topology
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Sorry I was out of station for few day. I somehow managed to mesh the geometry with shifted periodic topology. Figure 1 shows the blocking strategy.

Quote:
You shifted it the wrong way... You shifted it so that your mesh had to shift even more in the section... You want to shift it the other way so that the mesh crosses the section more orthogonally, not less...

Put the extra index on the other side...
Simon I think this time I have shifted the index in a right way such that the mesh crosses the section orthogonally. The minimum angle quality is 29.43. Figure 2 shows the mesh obtained using sifted periodic blocking. In figure 2 the red circle shows the clustering of cells. Is there any way to avoid such clustering? Will that cause any problem in during simulation?

I tried to insert C-grid around the airfoil as shown in the figure 3. The minimum quality is 40.59 (figure 4). There is no clustering of cells as shown in the figure 2 (without C-grid).
Attached Images
File Type: jpg Blocking.jpg.jpg (36.2 KB, 16 views)
File Type: jpg mesh quality shifted periodic.jpg (96.8 KB, 20 views)
File Type: jpg shifted with C-block.jpg (41.5 KB, 16 views)
File Type: jpg mesh quality C-block.jpg (96.8 KB, 20 views)
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Old   August 21, 2013, 09:41
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But when I insert C-grid, I am not able the control the node distribution (figure 1 in this post). I just applied 35 node count to the edge which just is above the suction side of the airfoil, but this mesh count is automatically copied to the remaining edges. I have no clue how it automatically copied to the other edges.

While the block without C-grid has a nice distribution as shown in the figure 2.
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File Type: jpg mesh distribution.jpg (89.7 KB, 13 views)
File Type: jpg shifted node count.jpg (42.7 KB, 14 views)
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Old   August 21, 2013, 12:11
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I assume that the problem with the control of node distribution is because when you run the o-grid command, all those vertices that you refer about become parallel. As a result, the number of nodes is copied through all of them.

There might be a way of controlling this in order to have more control over the mesh.

Regards,
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Old   August 21, 2013, 12:13
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.................

Last edited by cesarcg; August 22, 2013 at 09:54.
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Old   August 22, 2013, 12:06
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Quote:
I assume that the problem with the control of node distribution is because when you run the o-grid command, all those vertices that you refer about become parallel. As a result, the number of nodes is copied through all of them.
cesarcg, I also think the same.

I would like to know whether shifted periodic topology supports the C-grid around the airfoil.

Because the problem is that when I insert C-grid around the airfoil, I am not able the control the node distribution (figure 1). I just applied 35 node count to the one edge which just is above the suction side of the airfoil, but this mesh count is automatically copied to the remaining edges. I have no clue how it automatically copied to the other edges.

While the block without C-grid has a nice distribution as shown in the figure 2.

With shifted periodic topology I got a nice mesh but there is clustering of nodes at the outlet section (figure 3). Is there any way to reduce the clustering of nodes?

blocking files of shifted periodic topology
http://www.4shared.com/file/LBQWmObk/Front_rotor.html

blocking files of shifted periodic topology with C-grid around the airfoil
http://www.4shared.com/file/H3AOoKVk...otor_try1.html
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Old   August 22, 2013, 12:09
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Quote:
Originally Posted by cesarcg View Post
I assume that the problem with the control of node distribution is because when you run the o-grid command, all those vertices that you refer about become parallel. As a result, the number of nodes is copied through all of them.

There might be a way of controlling this in order to have more control over the mesh.

Regards,
César
delelte blocks inside airfoil permentaly
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Old   August 22, 2013, 17:40
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the blocks inside the airfoil are already deleted. i took a look at the blocking and was analyzing for a while, but i was not able to find out the reason why the number of nodes in one edge is reflected to the next one aside.

sorry venkatesh, let's see if simon and far give us a hint of how to solve this problem.

regards.
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Old   August 27, 2013, 01:32
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Quote:
Originally Posted by Far View Post
delete blocks inside airfoil permanently
I deleted the block of airfoil permanently but the mesh distribution remains the same on all the periodic edges. But Instead of splitting the edge in vertical direction of airfoil, First I selected the upper side block of the airfoil and then made two split along vertical direction (split 12 and 13 in figure 1) then I made two similar split in the lower side of the airfoil (split 4 and 5 in figure 1). By doing this way I am to control the mesh distribution of shifted periodic topology to certain extent.


I am able to understand what is happening in the mesh distribution.

Edge 1-2 and 10-11 are periodic, so if I assign a edge distribution (45) to edge 1-2, it is copied to edge 10-11 because of periodicity.



Since the grid lines (vertical gridline) has to run from edge 10-11 to the edge 2-3, the edge distribution of 10-11 is automatically copied to the 2-3.


Since the edge 2-3 and 11-12 are periodic, the edge distribution (45) of 2-3 is automatically copied to the edge 11-12.


I assigned a distribution of 22 to the edge 3-4 so it is copied to its the periodic side 12-13. Similarly for the edge 4-5 and 13-14.


The edge 5-6 and 14-15 are periodic, so it has same edge distribution.


Since the grid lines (vertical grid lines) has to run from edge 14-15 to the edge 6-7, the edge distribution of 14-15 is automatically copied to the 6-7.


Since the edge 6-7 and 15-16 are periodic, the edge distribution (45) of 6-7is automatically copied to the edge 15-16. The same is applied for the edge 7-8 and 16-17.


I assigned a distribution of 25 to the edge 8-9 so it is copied to its the periodic side 17-18.

The problem is that I didn't assign any distribution to the edge 5-6, but it is automatically copies the edge distribution of 1-2 to 5-6. I don't know why it copies the edge distribution.
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File Type: jpg 2D-edited.JPG (55.3 KB, 12 views)
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Old   August 27, 2013, 01:41
Default 3D-Shifted Periodic topology
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I tried to apply the same shifted periodic blocking strategy to the 3D blade. The blocking suits well for the propeller hub section (Figure1). But at the blade tip I get a highly skewed cells. Figure 2 shows the blocking at the tip of the blade. Figure 3 shows the blocking at the far-field. But I am not able to get a good quality mesh. I think I want to make several split along the span of the blade.

Should I want to do any changes in the blocking strategy?. I am waiting for your inputs. Please help me.

I have uploaded the tin and blk files in the links below.
http://www.4shared.com/file/RcrwfHny...grid_SPLI.html
http://www.4shared.com/file/Uml0N_Ka...grid_SPLI.html
Attached Images
File Type: jpg 3D blocking at Hub.jpg (49.7 KB, 14 views)
File Type: jpg 3D blocking at blade tip.jpg (45.7 KB, 13 views)
File Type: jpg 3D blocking at top far field.jpg (39.5 KB, 12 views)
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