
[Sponsors] 
August 16, 2003, 10:06 
axisymmetry set up for multiple axes of symmetry

#1 
Guest
Posts: n/a

Hi all!
I have a geometry with three different axes of symmetry. Is it now possible to define this problem as axisymmetric in Fluent. Thanks for any hint in advance. Greetings Varghese 

August 16, 2003, 12:24 
Re: axisymmetry set up for multiple axes of symmet

#2 
Guest
Posts: n/a

If all your domain is symmetric relatively to three axes, you can choose one of them and use the axisymmetric solver. Remember that FLUENT consider the xaxis as axis of symmetry.
If only a part of your domain is symmetric relatively to an axis, you can't use the asisymmetric solver for your case. Also, you have to consider flow behaviour before using an axisymmetric model. Is the flow really symmetric? If not, you're imposing a nonphysical condition. Hope this helps Hi ap 

August 17, 2003, 09:55 
Re: axisymmetry set up for multiple axes of symmet

#3 
Guest
Posts: n/a

Dear ap
I think I must clarify my problem little further that you can help me. In the calculational domain I have one major axis of symmetry at the centre of the domain and two minor axes of symmetry at two inlets. The axes of symmetry are however distinct. When the major axis turns 180° the minor axes would have revolved through 360°. I was thinking of multiple frame of references(MRF). But am not sure whether I can keep all the three domains stationary in that case. Hoping your further reflection on the problem Greetings Varghese 

August 17, 2003, 15:02 
Re: axisymmetry set up for multiple axes of symmet

#4 
Guest
Posts: n/a

I've some difficulties to visualize your domain because I don't know what you're modeling and what form it has. So it's difficult to give proper answers
Specifically, I'm not sure if your domain is a solid of rotation around the main axis of symmetry. Only in this case you can use the axisymmetric solver. Keep me up to date and email me if you want. Hi ap 

August 18, 2003, 04:40 
Re: axisymmetry set up for multiple axes of symmet

#5 
Guest
Posts: n/a

Dear ap
The domain is a large cylindrical tank, to which two inlets are open. The inlets themselves are radial jets into the tank, but not placed axially with the main tank. They shift themselves away from the central axis and this is the main problem to model it in a single axisymmetric scheme. There are now a central axis of symmertry for the large tank and another two axes of symmetry centred on the two inlets. But all the three axes remain in the same plane, hence opening possibility of creating an axisymmetric model. The question is whether Fluent allows one to have three stationary axes of symmetry for the same calculational domain. Greetings Varghese 

August 18, 2003, 08:08 
Re: axisymmetry set up for multiple axes of symmet

#6 
Guest
Posts: n/a

If I'm not wrong, your geometry is something like this:
             < axis This model can't be solved using the axi solver, because of the presence of radial inlets. If you use the axi solver, representing your domain like:           < axis you'd obtain a circular inlet all along the cilinder circumference. You have two choices: 1) Use a 3D model which represent the whole domain. It's the best solution, but it's time consuming and computationally expensive. I think you can do this for sure if you're going to do a steady simulation. If you want to do an unsteady calculation the computational time will grow a lot. 2) Use a 2D model (not Axi) If you decide for the 2D model, you can use the Axis boundary condition to represent the main axis of symmetry.           < axis Honestly I don't see any significant advantage (reduction of computational time) imposing the symmetry condition at inlets. Hope this helps Keep me up to date Hi ap 

August 18, 2003, 10:24 
Re: axisymmetry set up for multiple axes of symmet

#7 
Guest
Posts: n/a

Dear ap
Thanks for the effort you make to help me. Sorry for causing confusion once again. The geometry infact look like this: The two inlets are not from the side, but from the top.   major axis It is a transient calculation, hence can be really expensive, if I donot make an approximation. As you may observe in the domain, the axes of the inlets donot coincide with that of the major axis. It is precisely the problem for the axisymmetric reductiion. (I really wonder how you manage to draw precisely. It was tough time for me to draw at least in this crude way.) Expecting further insights Greetings Varghese 

August 18, 2003, 11:08 
Re: axisymmetry set up for multiple axes of symmet

#8 
Guest
Posts: n/a

So, your domain is like
inlets  <>             _________________  < Major axis This can't be modeled using the axisymmetric solver because of the presence of the two inlets. You can try a 2D model, in which you can represent your whole domain, without considering symmetry. I don't know what model you're going to use, but you shouldn't have problem with grid dimension with this approach. Anyway, the best solution is always the 3D model...but it's really expensive for an unsteady calculation. P.S. To draw better, just insert your preformatted text between the HTML tags PRE put here your preformatted text and drawings /PRE PRE and /PRE has to be between <> Keep me up to date Hi ap 

August 19, 2003, 04:16 
Re: axisymmetry set up for multiple axes of symmet

#9 
Guest
Posts: n/a

Thank you very much Mr.ap
You spent considerable time for me. Thank you very much. I shall try the 2d model for my problem. But what if I use MRF? Is it really possible to use Multiple frame of reference when all the individual domains are stationary? These are the remaining questions. If you find some answers, please inform me. Greetings Varghese 

August 19, 2003, 05:43 
Re: axisymmetry set up for multiple axes of symmet

#10 
Guest
Posts: n/a

I never personally used multiple Multiple Frame of Reference, but I think that in your case it's easier the direct approach of a 2D model.
Anyway, I'll look for more info and tell you if I find something interesting. I'd like to know how big is your tank, just to extimate the mesh size. It's a pleasure to help other people which works in CFD Hi ap 

August 19, 2003, 06:34 
Re: axisymmetry set up for multiple axes of symmet

#11 
Guest
Posts: n/a

The tank is 12000m3 in size. So the 3d calculation can be extremely expensive. That is why I am looking for closer 2d approximations.
Thanks a lot Varghese 

August 19, 2003, 06:47 
Re: axisymmetry set up for multiple axes of symmet

#12 
Guest
Posts: n/a

That's a really big system. What about trying to use a scaled model?
Hi ap 

August 19, 2003, 07:42 
Re: axisymmetry set up for multiple axes of symmet

#13 
Guest
Posts: n/a

If axisymmetric simplification is not possible I will have to think in that direction.
Greetings Varghese 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
symmetry boundary conditions in cfx  lost.identity  CFX  41  May 22, 2013 07:21 
Forces in Symmetry  Matt  CFX  2  February 25, 2009 06:41 
Help with GNUPlot  Renato.  Main CFD Forum  6  June 6, 2007 19:51 
Symmetry plane error in solver  Santiago Orrego.  CFX  6  January 31, 2007 08:09 
Handling axisymmetry terms on the symmetry line  Sonny  Main CFD Forum  4  December 9, 2005 17:22 