# Help with the discretization of the source term!

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 September 22, 2009, 03:32 Help with the discretization of the source term! #1 New Member   Libo Qian Join Date: Sep 2009 Posts: 5 Rep Power: 10 Now I am doing numerical research on the turbulence, using FVM and collocated grids arrangement and Low Re turbulence model. Could you tell me how to discreteize the source term for u- v- k- epslion- equation with non-uniform grids. I've tried a lot of method, but I can't get correct solution. I don't know why? I'am very grateful for your advice!

 September 22, 2009, 06:09 #2 Senior Member     p ding Join Date: Mar 2009 Posts: 337 Rep Power: 11 which method did you use. Finite volume method or finite difference method. in the finite volume method, it is much easier.

September 22, 2009, 06:18
#3
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Libo Qian
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Quote:
 Originally Posted by ztdep which method did you use. Finite volume method or finite difference method. in the finite volume method, it is much easier.

Finite volume method!
I don't know how to deal with the source term correctly!
With non-uniform grids

 September 22, 2009, 23:51 #4 Senior Member     p ding Join Date: Mar 2009 Posts: 337 Rep Power: 11 Dear friends: Since the FVM is used. the grid points are always placed at the center of the control volume. We only need to evalue the derivative at the interface by iterpolation. we can caculate all the source term. Could you please detail which source term trouble you. Regards

September 23, 2009, 00:19
#5
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Libo Qian
Join Date: Sep 2009
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Quote:
 Originally Posted by ztdep Dear friends: Since the FVM is used. the grid points are always placed at the center of the control volume. We only need to evalue the derivative at the interface by iterpolation. we can caculate all the source term. Could you please detail which source term trouble you. Regards
The u- and v- source term!
Actually, I've discretized the source term using FVM and coded it. But the results became divergent sudenly during iteration process. I mean in this step the results is convergent, while it will become divergent next step.
I don't know why?
Should I limit some parameters?
If so, which?
Thank you!

 September 23, 2009, 00:29 #6 Senior Member     p ding Join Date: Mar 2009 Posts: 337 Rep Power: 11 which alogirithm did you use. Have you validate your code? If your code is correct, i think you may try to lower the realxation parameter for u and v. BY the way, which method did you use to solve the linear algrebra equation.

September 23, 2009, 01:47
#7
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Libo Qian
Join Date: Sep 2009
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Quote:
 Originally Posted by ztdep which alogirithm did you use. Have you validate your code? If your code is correct, i think you may try to lower the realxation parameter for u and v. BY the way, which method did you use to solve the linear algrebra equation.
SIMPLER, collocated grid, non-uniform grid
Yes, I've validated my code: lid-driven cavity flow, natural convection in square cavity and so on.
I use ADI to solve the linear algrebra equation.
If I want to simulate turbulent natural convection in a square cavity, the best relaxation factor ? Could you give me some advice?
Thank you!

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