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August 29, 2004, 15:57 
How to use axisymmetric model?

#1 
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I am modelling a simple case(a jet in a cylinder.) In order to save some time, I choose axisymmetric model in solver. But it doesn't work until I change it to 2d model. Is there anybody can tell me what happen here?( In boundary condition, I set one side as axis. ) Another question: In my opinion, if I set boundary as axis, it should be axisymmetric model.Why should I choose it again in solver? Is there any contradict?


August 30, 2004, 03:21 
Re: How to use axisymmetric model?

#2 
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hi
you got to choose axisymmetry,to differentiate between symmetric and axisymmetric model. Axisymmetric model will have to sweep 360 degrees. 

August 30, 2004, 03:49 
Re: How to use axisymmetric model?

#3 
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Your axis must be 0x.


August 30, 2004, 08:29 
Re: How to use axisymmetric model?

#4 
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hi axisymetry will work for 2d only. you can't set axisymmetry for 3d. that to in 2d ,plane should be xyplane and axis of symmetry should be xaxis.


August 30, 2004, 11:25 
Re: How to use axisymmetric model?

#5 
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Thanks, I changed my model according to your suggestion, and it works


August 30, 2004, 11:34 
Re: How to use axisymmetric model?

#6 
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I too am using an axisymmetric mesh and it seems to work fine BUT when activated as axisymmetric, if I then do a "grid check" it says FAILED as "invalid axisymmetric gridthere are 290 nodes below the xaxis" If I switch back to 2D only grid check is fine. I have orientated xaxis as rotational axis and set BC accordingly. What, if anything, have I done wrong?
Chief 

August 30, 2004, 15:55 
Re: How to obtain mean flow

#7 
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hi, I am modeling packed bed column. I would like to know that I can I obtain/extract mean flowrate for the selected region in the packed bed reactor? Thanks Lee


August 31, 2004, 01:59 
Re: How to use axisymmetric model?

#8 
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hi There shd not be any element below Xaxis for axisymmetric problem. Try to change the geometry in gambit and orient in XY plane, do meshing & then import the mesh in Fluent with Axisymmetric.
Mahesh 

August 31, 2004, 10:04 
Re: How to use axisymmetric model?

#9 
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Mahesh,
thanks. I have a correct grid and mesh when 2D option is selected. A grid check passes fine. When the axis of rotation (also the x axis) is defined as an axis BC and the axisymmetric model is selected the grid check then fails. It is as if when the grid is rotated around the central axis it counts the nodes which have been swept around as being below the x axis. Well of course they would be because they have been swept around 360 degrees! Perhaps it is just a software glitch. The simulation seems to run fine anyway but I do not have the confidence to ignore the error message. I know that the bouyancy model I am using is very unstable and I am just trying to cover any possible areas of ambiguity. cheers Chief 

September 1, 2004, 18:45 
Re: How to use axisymmetric model?

#10 
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when you have axisymmetric shape you must modeling only one half of the problem then define>models > solve > axisymmetric then other condition and iterate


September 2, 2004, 08:42 
Re: How to use axisymmetric model?

#11 
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1)For axisymmetrical cases, the mesh must lie in the +y half of the plane. Fluent will use the xaxis as the axis of rotation. Any portions of cells falling below the xaxis will result in negative volumes.


September 2, 2004, 11:19 
Re: How to use axisymmetric model?

#12 
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ok cheers
Chief 

July 30, 2011, 07:46 

#13 
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soroush.armd@yahoo.com
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hi,i want to model a rotational disk,which one should i choose?axisymmetric or axisymmetric swirl?(i don't have a swirling flow!)
in addition,we could assign rotational speed to walls in both models,what is the difference between them? tnx. 

August 1, 2011, 09:20 

#14 
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JP
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Axisymmetric model is used when the geometry is axisymmetric (for example, flow through a pipe, where you can model just a 2D halfsection of the pipe). Here, there is no flow in the zaxis.
In axisymmetric swirl, there is swirling flow in the zaxis (normal to the geometry plane). In your case, you can model it like a stirred tank, by giving a rotational velocity to the walls. 

August 2, 2011, 05:23 

#15 
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soroush.armd@yahoo.com
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Thank you for your reply
I am trying to model a flow on a rotating disk,so I have a velocity component normal to the plane,you mean that I should use axisymmetric swirl model? tnx! Last edited by soroush; August 5, 2011 at 18:53. 

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