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.

Try SIMPLEC if not used so far.

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.

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.

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.

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.

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.

Use finer mesh.