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-   -   [ICEM] 2d hemisphere in wind tunnel (https://www.cfd-online.com/Forums/ansys-meshing/102816-2d-hemisphere-wind-tunnel.html)

aftertime June 3, 2012 13:27

2d hemisphere in wind tunnel
 
i just wanna calculate drag of a hemisphere in wind tunnel .i had a problem in first step when i tried generate mesh file in icemi . i dont know which far field is better . i tried some but i had problem in aspect ratio . if some one can help me it would be great . i must add that wind hit the flat side of hemisphere in tunnel . sry for my bad english

Far June 3, 2012 16:20

attach geometry file

aftertime June 4, 2012 09:09

1 Attachment(s)
i attached my icem file with a random farfield that i dont know if its good or not . tnx for your help

Far June 4, 2012 10:25

2d case..... Shouldn't it be 3d?

aftertime June 4, 2012 11:18

our teacher did it for a sphere with a bigger sphere for far field and as far as i know we do it in 2d and the axis line make it a perfect sphere . for my case i did same thing with hemisphere . for a sphere mesh had good quality but for hemishpere the flat line causes some aspect ratio problem .

Far June 4, 2012 11:33

My favourite post
 
I like this post very much http://www.cfd-online.com/Forums/ans...sh-fluent.html
It is classical work using ICEM.

aftertime June 4, 2012 12:23

the topic you linked is great but i feel my issue is very simple and primary

the project our teacher wanna us to do is a simple one like the one he did in class (because we are beginner and amature )
here is a link for the one he did for sphere . he did it in 5 min and asked us do it for different geometry like mine(hemisphere)
and after that exported it to fluent . and i know what to do there for drag and ...
http://encodable.com/uploaddemo/files/sphere.zip
( i just wanna know how should i take my far field for a good blocking and after that meshing ) again sry for bad english ;)

tnx a lot for your attention and time .

Far June 4, 2012 13:12

1 Attachment(s)
Ok . Done in five minutes (I wasn't counting :p.)

http://img403.imageshack.us/img403/2716/12531369.png

http://img818.imageshack.us/img818/646/30150213.png

Far June 4, 2012 13:26

Your case is much difficult than your teacher did.

diamondx June 4, 2012 13:26

2 Attachment(s)
here is how i changed the far field, of curse you need refinement so you can capture boundary layer. i suppose you know how to play with it. i'm sure there is a better blocking strategy

aftertime June 4, 2012 13:33

tnx man you helped alot . now i must look at it and figure it out how u did that ( im amature as u know :D)
thank you very very much

Far June 4, 2012 13:40

Quote:

i must add that wind hit the flat side of hemisphere in tunnel
From left to right? Any angle of attack?

aftertime June 5, 2012 08:00

yes From left to right and no angle . btw you split it to 9 blocks ?

Far June 5, 2012 08:56

I just made three half ogirds. one for body, one for boundary layer and one for outer layer

aftertime June 5, 2012 12:47

I worked on what you suggested and here is what i did ( i should thank diamondx too ) . i think it has lots of problem . i exported it to fluent and when i checked quality the Minimum Orthogonal Quality was 6.62394e-01 . i dont know how i can enhance the quality .
http://uploading.com/files/c218e433/New%2Bfolder.zip/
and something else . i need check the drag coefficient from experiment with what i calculate . do you have any idea where i can find one? i search a little for it but i didnt find any .
again thanks for your help

* sry that i upload my file in different place . i just wanna some expert (like you ;) )see it with detail and help me correct mine

Far June 5, 2012 13:31

0.6 is very good quality. Minimum needed is 0.01 by fluent. Meshing is good, but you have very fine mesh in far field..

reza45000 June 5, 2012 15:41

3D hemisphere
 
1 Attachment(s)
Hi, I have some problem related to this topic: I want to compute drag coefficient on a hemisphere and I know that the best way is an axisymmetric simulation. but for training I want to run a 3D simulation and need a 3D mesh.
actually I couldn't make a good one with ANSYS ICEM!
could you please help me?
Thanks.:)

Far June 5, 2012 16:09

Follow shpere-cube tutorial. What do you mean by good quality?

Far June 5, 2012 16:41

1 Attachment(s)
were you looking for this. Just deleted lower part of sphere!!! do you need it? I am not sure.

Far June 6, 2012 11:09

1 Attachment(s)
try this.......strategy is similar to sphere-cube tutorial

Far June 6, 2012 11:48

I am not happy with mesh. I dont know why mesh goes circular to square shape and then again square to circular. In this type of geometry where internal and external parts have similar shape, we should have the very good looking circular mesh. Any idea why this is happing?

http://img337.imageshack.us/img337/3862/51976330.png

http://img684.imageshack.us/img684/8881/58104809.png

http://img72.imageshack.us/img72/7494/21404523.png

http://img215.imageshack.us/img215/2884/68130736.png

reza45000 June 7, 2012 02:37

1 Attachment(s)
Quote:

Originally Posted by Far (Post 364888)
Follow shpere-cube tutorial. What do you mean by good quality?

I Followed it but the main problem is the bottom circle of the hemisphere. It itself need a 2D O-grid but in 3D blocking it is not possible as I know.
here is a 2D o-grid for a circle.
http://www.cfd-online.com/Forums/att...1&d=1339053729

reza45000 June 7, 2012 04:07

1 Attachment(s)
Quote:

Originally Posted by Far (Post 364891)
were you looking for this. Just deleted lower part of sphere!!! do you need it? I am not sure.

it is impossible because Left Far-field and Right Far-field are Inlet and Outlet or vice versa.

Quote:

Originally Posted by Far (Post 365049)
try this.......strategy is similar to sphere-cube tutorial

as you mentioned it is not a good one, look at the min angle: we have 0-9 degree cells.http://www.cfd-online.com/Forums/att...1&d=1339053637

Far June 7, 2012 04:35

No, It is not true. You must have activated solid part. I was talking about the general mesh shape otherwise quality is good and angle is higher than 40.

I guess we are on different track. I guess circle should be hollow. Can you describe your problem again with geometry pics to be modelled and some additional description?

reza45000 June 7, 2012 05:49

1 Attachment(s)
Quote:

Originally Posted by Far (Post 365186)
No, It is not true. You must have activated solid part. I was talking about the general mesh shape otherwise quality is good and angle is higher than 40.

I guess we are on different track. I guess circle should be hollow. Can you describe your problem again with geometry pics to be modelled and some additional description?

Here is a sample picture: the hemisphere is solid not hollow
http://www.cfd-online.com/Forums/att...1&d=1339058837
and we need farfield as I created in the geometry file.

Far June 7, 2012 06:30

Ok , got it. Nevertheless, we still make the hemishpere as hollow since fluid is not going inside.

In this case the far feild on the other side should be rectangular in shape to ease the meshing.

Far June 7, 2012 06:45

In the mean time for hemisphere section, use strategy we have just discussed. And in the other part with flat end (cylindrical enclosure), use simple topology and then create o-grid inside circular base all the way to end of cylindrical domain. Got it?

reza45000 June 7, 2012 07:41

Quote:

Originally Posted by Far (Post 365214)
Ok , got it. Nevertheless, we still make the hemishpere as hollow since fluid is not going inside.

In this case the far feild on the other side should be rectangular in shape to ease the meshing.

I think it has no difference. The block associates with the far field whether in sphere shape or rectangular.

Quote:

Originally Posted by Far (Post 365220)
In the mean time for hemisphere section, use strategy we have just discussed. And in the other part with flat end (cylindrical enclosure), use simple topology and then create o-grid inside circular base all the way to end of cylindrical domain. Got it?

Sorry I didn't:confused:.
I think my problem is the mesh on the bottom of hemisphere (as I showed in previous comments) that we should make a 2d o-grid on that circle but I couldn't do it.
If you have time to make a correct blocking, I will appreciate;).

Far June 7, 2012 07:43

I have already started to work on this. Going to post it shortly

Far June 8, 2012 09:21

Done
 
1 Attachment(s)
Done. It has some tricky part, when I was trying to snap vertices to hemisphere. Unlike the space cube tutorial where all things were done nicely with associate vertex to point on the inner cube, but this is not the case with this problem.

Enjoy and let me know if you get same problem as discussed above.

Far June 8, 2012 13:52

pics
 
Pics:

http://img819.imageshack.us/img819/9939/88103190.png
http://img816.imageshack.us/img816/6307/16606127.png
http://img215.imageshack.us/img215/4139/22079432.png
http://img407.imageshack.us/img407/710/80107674.png
http://img838.imageshack.us/img838/2852/82813442.png
http://img692.imageshack.us/img692/1319/35161749.png

reza45000 June 11, 2012 04:40

1 Attachment(s)
Quote:

Originally Posted by Far (Post 365451)
Done. It has some tricky part, when I was trying to snap vertices to hemisphere. Unlike the space cube tutorial where all things were done nicely with associate vertex to point on the inner cube, but this is not the case with this problem.

Enjoy and let me know if you get same problem as discussed above.

Fantastic, I also did it and you can see. Thank you for your attention.You create a hemisphere part including the large circle. I create the hemisphere part exactly the hemisphere so in association process first I associate the bottom of block to bottom of hemisphere (using "associate edge to curve") and then associate the faces of my inner block to hemisphere part(using "associate face to surface") and finally using "snap Project vertices" vertices go to the right position and there is no need to move vertices manually.

Thanks again.

Far June 11, 2012 07:24

I learn to feel the ICEM
 
I guess, now I am feeling the ICEM from heart. For example in this case if you snap the outer block first and then inner block, you will get the mesh problems as I have stated previously. You have to snap vertices at once. So make all oblocks, change material and snap the vertices.

Mine vertices for inner block were placed at Y= 1.9, while Reza's vertices (same vertices) were found to be at Y = 2.9. When used above trick or method, I have also got the vertices at Y = 2.9.

Have fun.

Far June 11, 2012 07:26

Quote:

using "associate face to surface")
Dont use this method, this method is used for making the internal wall. You just need to change the material and you will get the mesh on hemisphere.

reza45000 June 11, 2012 08:46

Quote:

Originally Posted by Far (Post 365799)
Dont use this method, this method is used for making the internal wall. You just need to change the material and you will get the mesh on hemisphere.

I didn't exactly understand Why not to use it?
How do you associate the inner block to hemisphere?

Far June 11, 2012 08:54

When you delete the internal block or change its material, icem automatically makes the associations.

Far July 8, 2012 05:21

Quote:

Originally Posted by Far (Post 365055)
I am not happy with mesh. I dont know why mesh goes circular to square shape and then again square to circular. In this type of geometry where internal and external parts have similar shape, we should have the very good looking circular mesh. Any idea why this is happing?


I found the reason for this. This is because I have forgot to switch back transfinite degree = Quadratic to transfinite degree = linear (linear is default option), so ICEM made it my default method and I was wondering for weeks that this is bug in ICEM. But now things are good :D.

Mid and outlet plane with quadratic option:
http://img33.imageshack.us/img33/6284/84012066.png
http://img837.imageshack.us/img837/4931/98393900.png

Mid and outlet plane with linear option
http://img406.imageshack.us/img406/5254/92553335.png
http://img812.imageshack.us/img812/4431/39806727.png


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