Difference between 2D and 2D axisymetric
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 
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.

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 
Reference value for depth is 1..
pressure inlet and pressure outlet with no slip conditions on the walls.. 
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Thank you guys for ur replies..

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Daniele 
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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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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