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-   -   Greatly Urgent!!!!! Help me please. (http://www.cfd-online.com/Forums/fluent/49240-greatly-urgent-help-me-please.html)

MK September 11, 2008 16:51

Greatly Urgent!!!!! Help me please.
 
Dear Everybody

I am simulating an unsteady flow through a pipe. The cross-sectional area reduces to 10 percent in the middle. I mean the area is one tenth of the area at the begining or the end of the pipe.

I can not converge the problem in any method. I try changing any possible parameter, but the problem diverged. Could you please help me. I should also mention that I analyzed the problem very well with 50 percent area reduction.

I need your help as soon as possible.

Thanks a lot.

K.K.Singh September 12, 2008 08:28

Re: Greatly Urgent!!!!! Help me please.
 
Try SIMPLEC if not used so far.

MK September 12, 2008 13:27

Re: Greatly Urgent!!!!! Help me please.
 
Dear K.K.Singh

I appreciate your answer. I used the SIMPLEC, but the problem did not converged. If you have any other idea please make me known. Do you know where I can refer to?

Thanks a lot.

K.K.Singh September 12, 2008 16:37

Re: Greatly Urgent!!!!! Help me please.
 
Give more details like grids used, turbulence model, under relaxation factors etc. Have u tried node based gradient option instead of cell based gradient option? Try to refine mesh near the constriction by using adapt mesh command.

MK September 13, 2008 01:57

Re: Greatly Urgent!!!!! Help me please.
 
Dear K.K.Singh

I have used the Hex/Cooper mesh in the volume. The viscous model is laminar, but as I have checked the Reynolds number in the throat last night, it was over 10000, so the flow is turbulent. Does it make much error, if I use the laminar model for simulation?

Under relaxation factors are set as default in Fluent. I mean pressure=0.3 , density=1 , body force=1 , and momentum=0.7.

I should also mention that I have refined the mesh near the throat, but no improvement occured. By the way, where can I change node based gradient option to cell based gradient option?

Thanks a lot.

MK September 13, 2008 02:05

Re: Greatly Urgent!!!!! Help me please.
 
I forgot an item. If I need to use the turbulent model, please introduce the best one and tell me how to set related parameters?

Regards.

Madusuthanan September 20, 2008 06:51

Re: Greatly Urgent!!!!! Help me please.
 
you can set your turbulence model by using fluent menu DEFINE-Model-Visous, from that select the required turbulance model, The most used model is K-epsilon 2 equation model.Since you are dealing with pipe problem you have set the turbulence intensity and Hydarulic diameter in your boundary condition panel.

azadhoor September 29, 2008 15:19

Re: Greatly Urgent!!!!! Help me please.
 
Use finer mesh.


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