FLUENT: Oscillating Results for Cd and Cl values
 

Hi guys!
I have been dealing with a simulation that gives oscillating results for Cd and Cl values. For Cd values the oscillations go up to 15% in some cases.

The main goal is to obtain an optimum position (aerodynamically speaking) for a wing in an amphibian aircraft. So, I am running a steady simulation with half the model (assuming flow symmetry). Spalart-Allmaras as turbulence model.

I am using coupled (therefore semi-implicit) as the discretization scheme. At the beginning, I tried out using segregated schemes, but I came across with Turbulence divergences no matter the under relaxation factor or discretization order I used, so I switched to coupled.

Any advice on how to get rid of those oscillations? As far as I understand, that kind of error occurs due to mesh problems or numerical errors.

I would appreciate any insights into this.

I tried to increase Courant number, but it didn't seem to cause any effect on the amplitude of the oscillations.

For reference:
The mesh has around 1 300 000 cells and I am iterating 6000 times.

This can sometimes be due to unsteadiness in the flow and so the steady state struggles to converge to one solution. Consider running a transient to analyse this behavior further.