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April 28, 2011, 23:14 |
"Wall" boudary condition setting
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#1 |
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Joe
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Hello, everyone! I got puzzled by the solution result.
Here is my case: Air flows through a duct, and turns down to the reactor. In order to optimize the distribution of velocity and try to make the flow angle as vertical as possiple, a rectifier is settled at the turning(as Geometry shows:the rectifer is constitute of non-thickness plate,with the space of 80mm between each other and height of 300mm). The inlet air has a uniform velocity of 15m/s, and the rectifer was defined as wall in fluent. As the rectifer has such a short space between each plate, I imagine the flow should be almost vertical after going through the rectifer, while the solution turns out a different result(see Velocity_Magnitude and Pathline). There is a huge vortex at the turning. It's really curious, I wonder if I've wrongly set some parameters about the rectifer as Wall, or is ther any other reason? Thank you for your attention! Picture link: Geometry: http://imageupload.org/?d=4DBA293D1 Velocity_Magnitude: http://imageupload.org/?d=4DBA29E51 Pathline: http://imageupload.org/?d=4DBA29E61 |
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April 28, 2011, 23:18 |
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#2 |
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Joe
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As seen from the pathline,the rectifer seems has no effect to guide the flow going downstream vertically. In another word, it seems that as if there is no rectifer at all.
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May 2, 2011, 07:12 |
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#3 |
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Maxime Perelli
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check the velocity distribution close to the rectifier.
Big zoom on it. Check also vectors. You can post the picture. If you want you can also upload your dbs file on a share server, I can check your geometry (the first picture sounds like to be from gambit)
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May 2, 2011, 22:20 |
Thank you for your help
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#4 | |
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Joe
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Quote:
velocity distribution: http://imageupload.org/?d=4DBF5F541 vectors: http://imageupload.org/?d=4DBF5F551 I also want to upload the .dbs file on a share server, if you have any good suggestion about which server is OK, plz tell me. I can send the dbs file to you instead, if you would like to leave me your Email, thank you! |
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May 3, 2011, 01:45 |
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#5 |
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qingkai
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So courious, did you set the roughness of Wall bc?
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May 3, 2011, 01:55 |
wall roughness
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#6 |
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Joe
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Hi, sailor, thank you for your attention. I didn't set the roughness of Wall bc. Do you think that will impact the result? I didn't get a clue how to set that parameter. However, I think the roughness of the wall can cause viscous stress, which leads to the pressure drop on the rectifier layer, but I don't think that may heavily impact the direction of vectors after going through the layer.
Thank you again! |
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May 3, 2011, 07:44 |
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#7 |
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Maxime Perelli
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can you post picture of veocity contour, but really on the rectifer.
here: Sans titre.png I checked your geometry and it is ok. I already defined such interior face (split) as wall, and fluent defined it as a baffle (consistent results). So it is supposed to work...
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May 3, 2011, 23:58 |
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#8 | |
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Joe
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Quote:
I'm afraid I didn't catch what you said. Any way, thank you for your lasting care about my problem. Below is the velocity contour around the rectifier layer(the grids of rectifier is turned off). http://dl.dropbox.com/u/28013317/Velocity-contour.png |
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May 4, 2011, 01:09 |
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#9 |
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Maxime Perelli
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your plane seems to go through a baffle row... (the blue contours show the zero velocity at walls which is correct)
offset this plane in z direction (for being between 2 baffle rows) and repost picture. Then generate the same picture but on a yz-section
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May 4, 2011, 02:02 |
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#10 | |
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Joe
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Quote:
links, velocity-contour: http://dl.dropbox.com/u/28013317/Vel...our-update.png grids: http://dl.dropbox.com/u/28013317/grids.png |
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May 4, 2011, 02:19 |
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#11 |
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Maxime Perelli
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ok then try to refine your grid.
Typically you need at least 8 cells in a gap. But I would expect a flow rate even if you have just one cell in a gap. On your first picture (if the planes are placed between 2 walls) it seems you don't have fluid passing through the rectifer. Check if you don't defined top and bottom surfaces as wall (display/grid select only rectifer with option faces (light on) and check that the body isn't "closed")
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May 4, 2011, 03:39 |
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#12 | |
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Joe
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Quote:
I've checked the grids by the method you suggested. From the picture, it seems the grid is OK, and it is not a closed volume. I think if the rectifier was a closed volume(which means if I set the top face of the rectifier layer as wall by mistake) , there wouldn't be flow going downstream after the rectifier layer, however, from the calculation result, we can see flow running through the rest of the reactor. link, grids-rectifier:http://dl.dropbox.com/u/28013317/grids-rectifier.png |
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May 4, 2011, 03:43 |
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#13 |
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Maxime Perelli
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then check where the fluid is passing through.
Check velocity contour at section xz through the rectifier
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May 4, 2011, 03:49 |
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#14 | |
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qingkai
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Quote:
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May 4, 2011, 04:08 |
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#15 | |
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Joe
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Quote:
I think it might be caused by the fact that all cell nodes are on the wall(split faces), where the velocity is zero, then fluent may use the method of interpolation to calculate the velocity between the two walls, therefore, anywhere between the walls has a zero velocity. link, velocity-contour-xz-section: http://dl.dropbox.com/u/28013317/Vel...xz-section.png |
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May 4, 2011, 04:09 |
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#16 |
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Joe
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May 4, 2011, 05:14 |
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#17 | |
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Maxime Perelli
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Quote:
And since your geometry is symmetric, compute just on half of your domain (I assume your BC's enable you to use one symmetry plane)
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May 5, 2011, 06:10 |
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#18 |
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Joe
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