[anita]

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]

Boundary condition of the trapezoidal body is wall.