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-   -   Coarser mesh different pressure and velocity (http://www.cfd-online.com/Forums/openfoam-solving/59114-coarser-mesh-different-pressure-velocity.html)

anita February 20, 2008 05:59

Hi, I am new to CFD. I am try
 
Hi,
I am new to CFD. I am trying to simulate Karman vortex street with flow around a trapezoidal body in 2D. The mesh is 8cm high and 15cm long. The trapezoidal body is 7.5mm high.
the boundaries are a inlet (10m/s), a outlet, and 2 symmetryPlanes. Because it is 2D the front and back are empty boundaries. As solver I chose IcoFoam.

I started with a mesh with approximately 25800 cells. And I got a good solution. I simulated 500ms and it needed 18 hours.

To get faster solutions I made the mesh coaser (5700 cells). And the calculation time was only 30min. I still get a nice karman vortex steet. But now the calculated pressure is lower (only half of the value) and also the velocity changed.

Now I don't know which result is right.
How fine must a mesh be to get good results?
Why does the results change, if I change refinement ?

How long does calculation normally take? I only have one DualCore computer.

Can someone help me?
Sorry for my bad English.

Greetings

Anita

anita February 20, 2008 06:17

Boundary condition of the trap
 
Boundary condition of the trapezoidal body is wall.


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