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
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attach geometry file
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i attached my icem file with a random farfield that i dont know if its good or not . tnx for your help
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2d case..... Shouldn't it be 3d?
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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 .
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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. |
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 . |
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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 |
Your case is much difficult than your teacher did.
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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
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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 |
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yes From left to right and no angle . btw you split it to 9 blocks ?
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I just made three half ogirds. one for body, one for boundary layer and one for outer layer
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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 |
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..
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3D hemisphere
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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.:) |
Follow shpere-cube tutorial. What do you mean by good quality?
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were you looking for this. Just deleted lower part of sphere!!! do you need it? I am not sure.
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try this.......strategy is similar to sphere-cube tutorial
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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 |
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here is a 2D o-grid for a circle. http://www.cfd-online.com/Forums/att...1&d=1339053729 |
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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? |
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http://www.cfd-online.com/Forums/att...1&d=1339058837 and we need farfield as I created in the geometry file. |
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. |
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?
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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;). |
I have already started to work on this. Going to post it shortly
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Done
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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. |
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Thanks again. |
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. |
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How do you associate the inner block to hemisphere? |
When you delete the internal block or change its material, icem automatically makes the associations.
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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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