[frossi]

Hi,

I am running a steady state simulation in pseudo transient. My problem is that my residuals, lift, drag, and mass flow rate converge perfectly until at 1000 iterations, and stay like that until 2000 iterations. At this point they start diverging more and more (see pictures).

Also note that I am doing a parametric study. I keep the wing geometry and mesh the same, while only changing the velocity. My results for lower velocities (from Mach 0.2 to Mach 0.3) are right and stay converged. While when I run Mach 0.35 (the same case as the pictures) you can see how the results diverge. How come this problem arises only at higher velocities?

I also tried to change the timescale factor from 1 to 0.1 to 0.05 to 0.01, but it diverges in every case.

I also uploaded screens of my mesh.

How can I fix this problem? I would really appreciate help, I have been stuck on this for a long time.


Best regards to all.

[Светлана]

This is not really a good mesh. You have inflation next to the foil surface, but you also need additional mesh refinement at the foil tail which is where a lot of flow activity takes place.

With the current mesh, switching to a second-order solver may increase stability.

You could also consider using dynamic mesh in Fluent if you are lazy to make a proper mesh yourself. Dynamic mesh would adapt to the flow and could work well.

Please remember to do a mesh convergence study in your work. Test for the foil lift and drag for different mesh sizes.