[houkensjtu]

Hello everyone !
I'm trying to validate the result from icoFoam with the theoretical solution of hagen poiseuille flow. https://en.wikipedia.org/wiki/Hagen%...uille_equation


My mesh is a simple axisymmetric 2D pipe with a radius of 0.05m and 1m long. I defined a 10 degree wedge shape pipe, applied symmetry condition on the axis and "wedge" condition on the front and back surface. (As described in the openfoam user guide : https://cfd.direct/openfoam/user-guide/v6-boundaries/)


In order to avoid the flow bending at the entrance, I applied zeroGradient boundary condition for U at the Inlet and Outlet. For the pressure, I applied a fixedGradient at the Inlet and a fixed value at the Outlet so that the pressure won't float to random value.


I used the OpenFOAM foundation version of OpenFOAM (http://openfoam.org/) and the version is 5.x. The solver I used is normal icoFoam.


According to the theoretical solution, the pressure gradient I applied on the pipe should result in a parabolic velocity profile with a peak value of exactly 2m/s.


However, even after tried to increase the number of mesh or decrease the size of time step, I end up getting a velocity profile with a maximum value of around 1.98m/s . Although this 1% error might not be serious issue, I think such a simple laminar case should yield a more accurate solution.


I attached my case file if you would kindly have a look. Please suggest what might be wrong in my case. Thanks!


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UPDATE:


It seems that if I reduce the angle of the wedge model, the velocity profile gets closer to the theoretical solution. If I reduce the angle to less than 2 degree, the maximum velocity is now 1.99m/s.
But I still wonder, did I do everything correct in the modeling?