Cannot produce identical result between 3D and axissymmetric 2D

zjoy · March 5, 2014, 14:01

Dear Foamers,

I'm testing simpleFoam simulation of a steady incompressible laminar flow on an axissymetric 2D model and the 3D model. The 3D model is a simple straight pipe with narrowed radius in middle section. The 2D model is the wedge shaped pipe with two patches (front and back) of wedge angle < 5 degree. The conditions setup are same between the 2D and 3D models except the flow rate at inlet is adjusted according to the inlet area. However, the result is different, the inlet pressure (0.153) at 3D model is higher than the inlet pressure (0.141) at the 2D model, the difference is about 7%. I cannot figure out what's wrong with the input.Do you have any example or comment for producing identical result on 3D model and corresponding wedge 2D mode? Thanks!

BTW: I'm using OpenFoam version 2.2.2.

Thanks,
Steven

alexeym · March 6, 2014, 06:00

Hi,

Can you be more specific?

Can you post case files? If not: Densities of the meshes are identical? What BCs do you use? What's in your fvSchemes and fvSolution?

zjoy · March 6, 2014, 10:54

Thanks. Densities are not identical. I will try to use same meshing pattern to test the result. Boundary condition is volume flow rate at inlet with zero gradient of pressure and at outlet with zero gradient of velocity and fixed value of pressure.

alexeym · March 6, 2014, 10:58

What type of BC do you use at the axis?

YYLI · November 3, 2015, 17:20

Is this problem solved?
I am facing a similar one now.

henryk42 · November 6, 2015, 00:47

Hi,
I'm new to OpenFoam,
Anyway, I'm running a flow in a series of pipes and using axisymmetric model. I found out that I need around 8 cells along the radius to get flow rate in agreement with analytical formula.

March 5, 2014, 14:01	Cannot produce identical result between 3D and axissymmetric 2D	#1
zjoy New Member ZJoy Join Date: Mar 2014 Posts: 2 Rep Power: 0	Dear Foamers, I'm testing simpleFoam simulation of a steady incompressible laminar flow on an axissymetric 2D model and the 3D model. The 3D model is a simple straight pipe with narrowed radius in middle section. The 2D model is the wedge shaped pipe with two patches (front and back) of wedge angle < 5 degree. The conditions setup are same between the 2D and 3D models except the flow rate at inlet is adjusted according to the inlet area. However, the result is different, the inlet pressure (0.153) at 3D model is higher than the inlet pressure (0.141) at the 2D model, the difference is about 7%. I cannot figure out what's wrong with the input.Do you have any example or comment for producing identical result on 3D model and corresponding wedge 2D mode? Thanks! BTW: I'm using OpenFoam version 2.2.2. Thanks, Steven

March 6, 2014, 06:00		#2
alexeym Senior Member Alexey Matveichev Join Date: Aug 2011 Location: Nancy, France Posts: 1,938 Rep Power: 39	Hi, Can you be more specific? Can you post case files? If not: Densities of the meshes are identical? What BCs do you use? What's in your fvSchemes and fvSolution?

March 6, 2014, 10:54		#3
zjoy New Member ZJoy Join Date: Mar 2014 Posts: 2 Rep Power: 0	Thanks. Densities are not identical. I will try to use same meshing pattern to test the result. Boundary condition is volume flow rate at inlet with zero gradient of pressure and at outlet with zero gradient of velocity and fixed value of pressure.

March 6, 2014, 10:58		#4
alexeym Senior Member Alexey Matveichev Join Date: Aug 2011 Location: Nancy, France Posts: 1,938 Rep Power: 39	What type of BC do you use at the axis?

November 3, 2015, 17:20		#5
YYLI New Member Join Date: Mar 2015 Posts: 1 Rep Power: 0	Is this problem solved? I am facing a similar one now.

November 6, 2015, 00:47		#6
henryk42 New Member Henryk Zaleski Join Date: Sep 2015 Posts: 3 Rep Power: 11	Hi, I'm new to OpenFoam, Anyway, I'm running a flow in a series of pipes and using axisymmetric model. I found out that I need around 8 cells along the radius to get flow rate in agreement with analytical formula.