Symmetrical Model With Non Symmetrical Solution

fugu · November 7, 2007, 07:07

Dragos,
you were totally right: the flow past a sudden expansion is inherently unstable and asymmetrical
when Re exceeds a critical value. Even the RANS mean flow shows asymmetrical features at least for averaging times used in literature.
See De Zilwa et al. "Flows through plane sudden-expansion" Int. J. for numerical methods in Fluids 2000 32 313-329
As for Jason problem, I guess might help to make the geometry of the join between the main pipe and the smaller ones as gradual and smooth as possible maybe reducing its angle.
Hope it helps
Luca

dmoroian · November 7, 2007, 10:57

Hi Luca,
Thank you very much for the references, I'll try to get them.
Jason, as I remember, the asymmetry appears only for certain ratios between the inlet diameter and expansion diameter. In my oppinion, one of the solutions (besides that suggested already by Luca), you should increase this ratio (decrease the inlet diameter or increase the expansion diameter). It sould be easy to see that with the simple example from above. Just play with the diameters until you get the symmetric solution.

jason · November 8, 2007, 06:05

Hi,

Thank you for your comments and help. I don't want to take up any more of your time so I will carry on looking into this further and let you know if I manage to solve it.

Kind Regards

Jason

armin_h · December 10, 2007, 04:19

Hello all

would you please any one let me know how can i push flow into the pipe in openfoam?
I have created the geometry of the pipe and also the mesh.
I need to see the velocity profile which comes from the moving flow into the pipe.
I am new user of openfoam and i dont know how can i put the amounts for the u velocity and see the motion of the fluid inside the pipe.

I would appreciate any comments.

sorry if it is not an advance question.

Cheers
Armin

dmoroian · December 10, 2007, 06:21

Hello Armin,
I think it would be helpfulf for you if you download the case files mentioned above ( POST17811), and start from there.

Dragos

armin_h · December 18, 2007, 02:49

Dear Dragos

Appreciate abot the answer.
I will work for it.
SOrry i bother you.

Many Thanks again.

Kinds Regards
Armin Hosseinian

November 7, 2007, 07:07	Dragos, you were totally righ	#21
fugu New Member Luca Liberti Join Date: Mar 2009 Location: Rome, Italy Posts: 22 Rep Power: 17	Dragos, you were totally right: the flow past a sudden expansion is inherently unstable and asymmetrical when Re exceeds a critical value. Even the RANS mean flow shows asymmetrical features at least for averaging times used in literature. See De Zilwa et al. "Flows through plane sudden-expansion" Int. J. for numerical methods in Fluids 2000 32 313-329 As for Jason problem, I guess might help to make the geometry of the join between the main pipe and the smaller ones as gradual and smooth as possible maybe reducing its angle. Hope it helps Luca BlnPhoenix likes this.

November 7, 2007, 10:57	Hi Luca, Thank you very much	#22
dmoroian Senior Member Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 20	Hi Luca, Thank you very much for the references, I'll try to get them. Jason, as I remember, the asymmetry appears only for certain ratios between the inlet diameter and expansion diameter. In my oppinion, one of the solutions (besides that suggested already by Luca), you should increase this ratio (decrease the inlet diameter or increase the expansion diameter). It sould be easy to see that with the simple example from above. Just play with the diameters until you get the symmetric solution.

November 8, 2007, 06:05	Hi, Thank you for your comm	#23
jason Member Jason Dale Join Date: Mar 2009 Location: UK Posts: 80 Rep Power: 17	Hi, Thank you for your comments and help. I don't want to take up any more of your time so I will carry on looking into this further and let you know if I manage to solve it. Kind Regards Jason

December 10, 2007, 04:19	Hello all would you please	#24
armin_h New Member Armin Hosseinian Join Date: Mar 2009 Location: Perth, Western Australia, Australia Posts: 17 Rep Power: 17	Hello all would you please any one let me know how can i push flow into the pipe in openfoam? I have created the geometry of the pipe and also the mesh. I need to see the velocity profile which comes from the moving flow into the pipe. I am new user of openfoam and i dont know how can i put the amounts for the u velocity and see the motion of the fluid inside the pipe. I would appreciate any comments. sorry if it is not an advance question. Cheers Armin

December 10, 2007, 06:21	Hello Armin, I think it would	#25
dmoroian Senior Member Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 20	Hello Armin, I think it would be helpfulf for you if you download the case files mentioned above ( POST17811), and start from there. Dragos

December 18, 2007, 02:49	Dear Dragos Appreciate abot	#26
armin_h New Member Armin Hosseinian Join Date: Mar 2009 Location: Perth, Western Australia, Australia Posts: 17 Rep Power: 17	Dear Dragos Appreciate abot the answer. I will work for it. SOrry i bother you. Many Thanks again. Kinds Regards Armin Hosseinian

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