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April 12, 2013, 00:40 
Difference between 2D and 2D axisymetric

#1 
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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 
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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 
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Daniele
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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 
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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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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 

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Thank you guys for ur replies..


April 14, 2013, 11:19 

#7  
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Daniele
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Quote:
Daniele 

April 14, 2013, 20:14 

#8 
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Stuart Buckingham
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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
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April 15, 2013, 13:09 

#9  
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Daniele
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Quote:
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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