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January 19, 2007, 14:41 |
Converging problem of buoyancy flow
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#1 |
Guest
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Dear all,
I have reduced the under-relaxation factor, used 1st order scheme, follow every steps suggested by buoyancy simulation from the Fluent user guide, yet failed to obtained a converged solution. The simulated building block size is 20m x 20m x50m, the closing domain of outdoor air is 200m x 200m x 250m. Boundary conditions: 1 pressure inlet (top face of the domain) and 4 pressure outlets(4 side faces) For the mesh, I have produced a mesh with boundary layer growth factor (b/a) of 1.3, started at the first row (a)of 0.03 and the number of row of 4.The interval size of the mesh volume is 10. Thus, a fine mesh near the building wall surface and coarse mesh at the surface of the closing air domain is produced. (For Gambit meshing, I used meshing type T-Grid, and the elements option of Tet/Hybrid) As the solution did not converge, and so the velocity vectors produced looked unexpected. From your experience, can you suggest me about some important points I may ignore in making a good mesh or boundary conditions? And also, how many iteration steps you usually see when the solution starts to converge from your experience? Thank you very much Regards, Cadrian |
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January 19, 2007, 15:02 |
Re: Converging problem of buoyancy flow
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#2 |
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which multiphase are you using? are you using any turbulence model? if yes, check your y_plus/ aspect ratio of mesh.. Try with reduced URF..
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January 19, 2007, 15:43 |
Re: Converging problem of buoyancy flow
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#3 |
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Dear Sujith,
I am using the Boussineq model of the air. And also I am using k-e turbulence model. And I have tried a under-relaxation factor as low as 0.7 (is that enough?) Anyway, do you have any suggested value of y_plus/aspect ratio of mesh? Thank you so much =) Cadrian |
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January 19, 2007, 17:08 |
Re: Converging problem of buoyancy flow
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#4 |
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I had similar issues with buoyancy flows... perhaps there is no stationary solution, so you should use the unsteady solver and see what happens!
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January 19, 2007, 18:09 |
Re: Converging problem of buoyancy flow
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#5 |
Guest
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Hi Cadrain,
try running it transient with say 5 iterations per time step. You can calculte a velocity scale given Bak_Flow |
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