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March 25, 2014, 04:39 |
Natural convection in water
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#1 |
New Member
Victor Pannel
Join Date: Mar 2014
Location: Marseille (France)
Posts: 12
Rep Power: 12 |
Hi guys,
Here is the case: I want to modelize the water natural convection. The geometry is quite simple: it's a parallelepiped rectangle. A surface heatsink represented by a quarter circle in a corner ( the center coordinate is (0,0,0). MESH: Polyhedral Mesher Prism Layer Mesher Surface Remesher BC: All the surfaces are wall except the 2 vertical walls between the surface are symetrics. The physics models I used are: Boussinesq Constant density Coupled Flow/energy Gradients Gravity Laminar 3D Liquid I tried steady and unstead but the calculation do not converges. The main problem is the Z- momentum (him residuals states at around 1-10) I saw that replacing the two walls and the top by outlet pressure instead of walls could gives results, but when I tried I had reversed flows.. Anyone can tell me wich are my mistakes and which parameters I have to modifiate? Thanks for reading |
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March 25, 2014, 09:16 |
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#2 |
Senior Member
Ping
Join Date: Mar 2009
Posts: 556
Rep Power: 20 |
natural convection is in real life an unsteady process so i would be surprise if you can get a converged solution in steady state.
so i would be running unsteady and testing a few time steps and checking the courant number and dumping scene images to check for reasonable flows. also when using the physics you have mentioned be careful to set the coef of expansion of the fluid since star-ccm+ sets this to 0. for some reason it is not in the material database. |
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March 25, 2014, 10:25 |
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#3 |
New Member
Victor Pannel
Join Date: Mar 2014
Location: Marseille (France)
Posts: 12
Rep Power: 12 |
It's working now for some reasons!
Thanks for your answer. Last edited by CneSpaulding; March 26, 2014 at 04:40. |
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May 5, 2014, 14:09 |
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#4 |
Senior Member
Joe
Join Date: Feb 2012
Location: Canada
Posts: 111
Rep Power: 14 |
Ping,
Could you please explain what did you do to fix it? what is you Ra number? How did you understand that it converged? just by checking the residuals or you defined some points/lines inside your domain and look for a converged of averaged value for the parameter you defined... Thank you, Hooman |
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May 7, 2014, 06:07 |
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#5 |
Senior Member
Ping
Join Date: Mar 2009
Posts: 556
Rep Power: 20 |
you had better ask CneSpaulding about how he solved his case.
but you should always have some relevant reports being monitored and plotted to help judge convergence, even for steady state cases. |
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May 13, 2014, 08:25 |
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#6 |
New Member
Victor Pannel
Join Date: Mar 2014
Location: Marseille (France)
Posts: 12
Rep Power: 12 |
Hi,
Sorry for the late answer, I'm quite busy this month. I used the following parameters: Implicit Unsteady Boussinesq Coupled Flow/Energy The 2 walls are adiabatic And I used a better mesh. I just checked the residuals plot, when I saw that all the parameters converged under 10-5 I decided to stop the calculation. |
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July 8, 2015, 11:14 |
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#7 |
New Member
Gregory Hannam
Join Date: Mar 2015
Posts: 7
Rep Power: 11 |
I still seem to be really struggling with this.
The fluid looks like its heating up its just not rising... I have the models set up like above, what am I missing? |
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July 8, 2015, 11:17 |
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#8 |
Senior Member
Joe
Join Date: Feb 2012
Location: Canada
Posts: 111
Rep Power: 14 |
greg_2666,
What's the problem exactly? Hooman |
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July 9, 2015, 04:18 |
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#9 |
New Member
Gregory Hannam
Join Date: Mar 2015
Posts: 7
Rep Power: 11 |
So all it is, is a simple model of a server immersed in water. It is a 90 cm board held vertically in the fluid. It has two hot chips towards the bottom which should heat the liquid up next to it and in turn the water should rise.
The models activated are: Boussinesq, Constant density, coupled energy/flow, gradients, gravity, K-e, liquid (H2O), steady, 3d, laminar, 2 layer wall treatment The board is 90cm high and I have made a block on the surface and subtracted it to give the fluid region. I set the temps of the two chips (modeled as 2 10x10 squares) at 320K and set the reference temp at 288K. I've just realised i don't have a heat sink, i've only set the wall temperatures of the fluid block at 278K I'm not seeing a heat transfer from the heat source to the water... I think it is not conducting heat from the source into the water, I've checked the properties and they all seem fine.. Last edited by greg_2666; July 9, 2015 at 09:44. |
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