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March 14, 2012, 09:07 |
Buoyancy driven flow
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#1 |
New Member
Hamid
Join Date: Mar 2012
Posts: 20
Rep Power: 14 |
Hi everybody,
I'm going to solve a simple flow over flat plate and I'm going to have heat equation and buoyancy effects in my flow. My domain size is 1500(height)x6000x6000 [m] and my first grid center is located 0.03 away from the ground. I have periodic lateral BC, Symmetry top BC and no-slip wall BC. I can simulate the flow when I have a neutral case but with temperature it diverges very fast. Do you have any idea what could be wrong? Note that with this size Grashof number becomes enormous, but I don't know if that's the problem. I appreciate all your suggestions |
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March 14, 2012, 14:07 |
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#2 |
New Member
Join Date: Jun 2009
Posts: 9
Rep Power: 17 |
How about first trying with reducing your URF and making your solution more stable.
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March 14, 2012, 14:26 |
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#3 |
Senior Member
Andrew
Join Date: Mar 2009
Location: Washington, DC
Posts: 211
Rep Power: 18 |
it sounds like a grid problem. Especially with buoyancy driven flow. Most of the interaction will be close to the wall, so you need a good grid in that region. I am assuming your plate is vertical and not horizontal.
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March 15, 2012, 08:02 |
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#4 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73 |
maybe, it can be a case of numerical instability due to the high Gr number...
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March 15, 2012, 10:03 |
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#5 |
New Member
Hamid
Join Date: Mar 2012
Posts: 20
Rep Power: 14 |
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March 15, 2012, 10:11 |
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#6 | |
New Member
Hamid
Join Date: Mar 2012
Posts: 20
Rep Power: 14 |
Quote:
Now, even the temperature equation works fine but only if I disregard the gravitation. |
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March 15, 2012, 10:13 |
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#7 |
New Member
Hamid
Join Date: Mar 2012
Posts: 20
Rep Power: 14 |
I might also take a look at the block communications (it's a multi-block structured code I'm using) to see if something goes strange ...
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March 15, 2012, 10:15 |
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#8 |
New Member
Hamid
Join Date: Mar 2012
Posts: 20
Rep Power: 14 |
mmm, yeah, meybe, since it scales up as L^3 (L being characteristic length scale) ... but isn't it what normally happens? I mean I'm just simulating a small part of the real atmosphere with temperature stratification ...
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March 19, 2012, 11:39 |
problem partly solved, not sure if it's true ...
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#9 |
New Member
Hamid
Join Date: Mar 2012
Posts: 20
Rep Power: 14 |
Hi again,
regarding the issue with buoyancy driven flow, I tried to decouple temperature and momentum equations completely i.e. after the solution for pressure and velocities converge, I solve the heat equation and most importantly "add the buoyancy contributions". Seems it solved the issue ... I know it's a general practice to treat the heat equation like this (quasi-steady) but not sure if it's true when you have buoyancy? since buoyant force affects the flow field directly and might make it inaccurate ... |
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March 19, 2012, 11:56 |
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#10 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,897
Rep Power: 73 |
Quote:
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April 19, 2012, 05:46 |
show me by CFX
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#11 | |
Senior Member
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 16 |
Quote:
My problem is the same as yours. I have fluid flow with heat transfer and the buoyancy takes place through my model. Regards |
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May 15, 2012, 00:56 |
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#12 | |
Senior Member
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 16 |
Quote:
thanks for your good thread.However, I'm still sad because I asked to show me how until I do it after 2 months!!..some guys do not care about the others. you will feel better whan youbecome helpful member |
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Tags |
buoyancy flow, divergence, grashof number |
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