# Difference between 2D and 2D axisymetric

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 April 12, 2013, 00:40 Difference between 2D and 2D axisymetric #1 Member   Join Date: Apr 2012 Posts: 48 Rep Power: 6 Hello, Im solving a flow through circular pipe. I am specifying pressure drop. When I use a axisymetric case, I get the velocity as per the Hagen Poiseuille Equation. But when I try to solve it using a 2D case it gives me velocity exactly twice of the axisymmetric case. Or simply put the avg. velocity which I am getting after running a 2D case is twice as what I should get from the Hagen Poiseuille Equation. Where can I possibly go wrong while simulating these two cases? Thanks. Varad

 April 12, 2013, 00:45 #2 Member   Join Date: Apr 2012 Posts: 48 Rep Power: 6 Or simply put the avg. velocity which I am getting after running a 2D case is twice as what I should get from the Hagen Poiseuille Equation.

 April 12, 2013, 02:19 #3 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 995 Rep Power: 17 2d axisymmetric simulates a cilindrical pipe, 2d simulation a square/rectangular duct; what are your boundary conditions?under reference values what is the value for "depth"? Daniele

 April 12, 2013, 09:30 #4 Member   Join Date: Apr 2012 Posts: 48 Rep Power: 6 Reference value for depth is 1.. pressure inlet and pressure outlet with no slip conditions on the walls..

April 14, 2013, 02:04
#5
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Sijal
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Quote:
 Originally Posted by ghost82 2d axisymmetric simulates a cilindrical pipe, 2d simulation a square/rectangular duct; what are your boundary conditions?under reference values what is the value for "depth"? Daniele
I would like to add further. For shapes other than cylinder, rectangle and square you have to model it as quarter or half symmetrical at least (3D).

 April 14, 2013, 11:06 #6 Member   Join Date: Apr 2012 Posts: 48 Rep Power: 6 Thank you guys for ur replies..

April 14, 2013, 11:19
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Daniele
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Quote:
 Originally Posted by vagaikwa Reference value for depth is 1.. pressure inlet and pressure outlet with no slip conditions on the walls..
This means that when you are simulating a 2d model, you have a rectangular duct which has an inlet/outlet area of 'your coordinate' x 1 m (depth under reference values).

Daniele

 April 14, 2013, 20:14 #8 Senior Member   Stuart Buckingham Join Date: May 2010 Location: United Kingdom Posts: 267 Rep Power: 17 No, this is incorrect. 2D models are infinitely long in the spanwise direction (Z axis, which you are not modelling). Any geometry that has a finite span, or does not have a perfect cylindrical cross section at all stations along its length must be modeled in 3D. Stu __________________ http://bc247.wordpress.com

April 15, 2013, 13:09
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Daniele
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Quote:
 Originally Posted by stuart23 No, this is incorrect. 2D models are infinitely long in the spanwise direction (Z axis, which you are not modelling). Any geometry that has a finite span, or does not have a perfect cylindrical cross section at all stations along its length must be modeled in 3D. Stu
yes you are right, that means that since you are not modeling the z coordinate, you are assuming that interactions occur in the x-y directions.
However I meant that if you are assigning for example an inlet velocity of 1 m/s and you have set a depth of 1 m with the inlet edge 0,2 m long your resulting flowrate will be 0,2x1x1 m3/s.
For sure you are not modeling z interactions.

Daniele

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