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Old   April 6, 2010, 22:48
Default Unable to get rid of skewness- divergence
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Zaqie
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Hi Simon,

Reply to post#37...

Bad news!!....my simulation is diverging at velocities where calculations are absolutely necessary.

I tried one more thing. Instead of the sharp wedge shaped tip, I gave a cut in the geometr., to see if it will help in reducing skew.

It doesnt help.

I tried increasing the node at collapsed end, reducing node numbers, nothing seems to work. Also tried collapsing only till the blade block and not till far field.

Nothing worked. Is there any way out to control the tip?

Please help.

Regards

Zaqie Reza
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Old   April 7, 2010, 10:56
Default Shifted Periodic
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Simon,

Thanks again for the pointers on turbine meshing, I've been working through them and (as expected) have come up against some trouble (mainly just with the use of the O-grids). I don't want you to have to spell out each and every small step but if you could answer a few questions that would be great.

1) The use of the two quarter O-grids for the shifted periodic makes sense but I'm having trouble getting the same arrangement of edges in your picture. Would you make 4 splits around the blade first, then collapse the trailing edge and then use the O-grid function? or would you do it in a different order?

2) For the rounded section of the hub ('0' to '2' on your picture) have you first split along '2', then along the axis, and then used 2 quarter O-grids? The reason I ask, is that I've tried that and when I try to add the internal faces to the O-grid, the split propagates into the next blocks.

Many thanks,

Andy
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Old   April 10, 2010, 08:58
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How to set periodic boundary with tetra-prism meshing .

Please help.

Regards

Zaqie[/QUOTE]
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Old   April 10, 2010, 09:32
Default periodicity
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Go to “mesh tab => Global Mesh Setup => Set up Periodicity”

you can do it there.
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Old   April 10, 2010, 21:09
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Quote:
Originally Posted by Zaqie View Post
Go to “mesh tab => Global Mesh Setup => Set up Periodicity”

you can do it there.
thanks for you reply.
yes,i had done,but i can find nothing change. is there any sill in the opperation?
my module is a semicolumn with a wind turbine balde in it.
my step:
mesh tab => Global Mesh Setup => Set up Periodicity=>Set up globle mesh=>mesh.
is there something wrong?
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Old   April 11, 2010, 09:44
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Thanks very much for your help. I've solve this problem.
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Old   September 26, 2010, 22:28
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Thanks very much, I really appreciate that
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Old   November 11, 2011, 12:56
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Quote:
Originally Posted by Zaqie View Post
Hi Simon,

Reply to post#37...

Bad news!!....my simulation is diverging at velocities where calculations are absolutely necessary.

I tried one more thing. Instead of the sharp wedge shaped tip, I gave a cut in the geometr., to see if it will help in reducing skew.

It doesnt help.

I tried increasing the node at collapsed end, reducing node numbers, nothing seems to work. Also tried collapsing only till the blade block and not till far field.

Nothing worked. Is there any way out to control the tip?

Please help.

Regards

Zaqie Reza
Hello everybody,

I have some questions about meshing for the 3d blade inside the periodic air volume.

a) With the last meshing method asked by Zaqie, do I only get a surface mesh, i.e. for the blade and the for the walls? If so, how do I create a volume mesh? Because I want to study what happens to the flow downstream the turbine?

b) Since I only have two blades, can I apply the same concept (periodic) to a 180 degree 'slice' volume?

c) Do I have to use Multiple or Single reference frame? Is the whole volume rotating in this method?


Thank you very much,

best
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Old   November 15, 2011, 20:20
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a) If you are doing 3D Hexa blocking, you get the volume mesh by default. Perhaps you do not have it displayed? Run a scan plane to see it or right click on blocking and check info to see how many hexas are in your model... If we just displayed all the hexas by default it would be an incomprehensible pile of mesh and would take a lot more memory to display it, so by default we display the faces and you can use scan planes to see thru the volume...

b) Yes, you could have 180 degree periodic...


c) That depends on your model. In some cases you may have a rotating portion inside a shroud that is not periodic and not rotating... In that case you would create an artificial cylinder to be the boundary between the two regions... You would rotate the region inside the cylinder and not rotate the region outside. If you are just doing a blade passage you could probably assume the whole regions is rotating... Just remember that when you set up all your boundary conditions.
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Old   December 4, 2011, 13:48
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Quote:
Originally Posted by Zaqie View Post
I know I have been persistent. I am not really getting it right.

Can you give me a method to block the blade. I am having trouble at the hub area, the problem as mentioned below

I collapsed the blade section. Since collapsing of blade section was leading to collapse of section underneath it effecting the hub area, i split the blade block to two, one a larger one above and a smaller one below. Then I used index control for the upper larger section for collapsing for the blade. Associated vertices and curves to edges of the blade. Since the splitting of upper block created a additional block in the hub area , i merged the two blocks inside the hub. Then I tried creating the ogrid using the two blocks, i.e one in the blade and and the other at the hub. But I got an error message on the lines of "Ogrid could not be created".

Please help. If possible please give me tips on blocking the domain completely. I am really stuck.

Zaqie
Hi, how's your simulation going? i am doing the similar thing as you did, but i got stuck at 1. mesh quality, 2. mesh export; when i collapsed the block, i got some very bad elements as well, are there anything i can do on it to get rid of it? then when i try to export the mesh(the solver is Fluent v6), it shows the error "Fluent format doesn't support 7 node HEXA element", do you have any idea?
really appreciate if you can give me some suggestions, i have been sturk here for one week~~

Best Regards,
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