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All're symmetrical , but fluid is not symmetrical ?

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Old   April 21, 2009, 21:38
Default All're symmetrical , but fluid is not symmetrical ?
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Hello , guys !

I've got a weird question : My model is totally axial symmetrical , other info. : Incompressible ideal gas , gravity enabled , and flow direction is opposite towards the gracity . and after my enabling energy equation , starting calculation , converged , the result shows that the fluid vetor is not symmetrical ! The only asymmetry is the grid , will it affect the result ?
What more , when species transport model enabled , the fluid looks more symmetrical , and easier to converge , then what's the effection of s-t model ?
Thanks for any help !
Regards !
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Old   April 22, 2009, 00:35
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Basically, if your domain is symmetric and also your BC... depending on the flowfield properties (Re, etc...) it is possible that the fluid doesn't flow symmetrical.
The von Karman vortex are a good example
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Old   April 22, 2009, 08:11
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Did you try refining your mesh or doing a grid check? - maybe your mesh is too coarse
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Old   April 22, 2009, 23:06
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Quote:
Originally Posted by -mAx- View Post
Basically, if your domain is symmetric and also your BC... depending on the flowfield properties (Re, etc...) it is possible that the fluid doesn't flow symmetrical.
The von Karman vortex are a good example
Thank you for your answer !

Actually I've tried laminar , k-e , S-A , and it looks turbulence model is better , despite the velocity is low, and Re is between laminar vs turbulence . So would it poosible caused by turbulence model ?

And what's more I'm using Incompressible ideal gas model , which is sensitive with high temperature , and the temperature in my case is more than 1000C , so is there some better density model for this ?

Thanks again !

lee
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Old   April 22, 2009, 23:16
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Quote:
Originally Posted by mettler View Post
Did you try refining your mesh or doing a grid check? - maybe your mesh is too coarse
Thanks for your answer !

I think the mesh is fine enough , and grid check is done . Actually the geometry model is simple , what I'm curious is whether the grid really affect symmetry ?

What more , if energy equation is not enabled , the fluid is symmetric depending on the same mesh , so I doubt maybe there's a thing on temperature .

well , thanks again !

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Old   April 23, 2009, 01:07
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If you think that it's linked to the mesh, you can split your model on the symmetry plane, and mesh the splitted domain.
Then copy this volume, with reflect and mesh option.
Connect the symmetry planes (which should be superposed).
Finally you get your full domain, but with symmetric mesh.
Re-compute and check if the solution is symmetric or not
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Old   April 23, 2009, 01:53
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Quote:
Originally Posted by -mAx- View Post
If you think that it's linked to the mesh, you can split your model on the symmetry plane, and mesh the splitted domain.
Then copy this volume, with reflect and mesh option.
Connect the symmetry planes (which should be superposed).
Finally you get your full domain, but with symmetric mesh.
Re-compute and check if the solution is symmetric or not
Thank you for suggestion !
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Old   April 23, 2009, 02:02
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Further more , is there a proper density model for gas under high temperature ?

Thanks very much !

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