Troubleshooting: different results for different mesh on exact same geometry (Rectangular channel)

B_RahmanB_Rahman Member Posts: 4

Hello All! I have been running some simulations on a simple rectangular (square) channel on ANSYS Fluent, and analytically verified the results. 

I am facing two problems: (1) When I lower the mesh size (add more elements), keeping dimensions and other parameters fixed, the pressure drop somehow keeps increasing, even when the centerline velocity seems to converge. 

(2) To analytically verify the ANSYS results, I used Navier Stokes for a thin rectangular channel. I am aware that for a square channel, the error should be ~10%. Using the following equations I obtained the analytical centerline velocity and pressure drop values which differ greatly from the ANSYS calculations. While I understand that the centerline velocity of fully developed flow will not be the same as the inlet velocity, I am confused as to how the analytical centerline velocity can be an order of magnitude over the inlet velocity.  

Does anyone have some insight on how to resolve these two issues? 

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