[AamirSultan]

Hello Everyone , Hope you are doing fine .
I am running a 2D analysis of flow over an airfoil at Re Number=10^5
I am running a steady state , density based solver simulation of the case .
At higher angle of attacks >= 10 degrees , I am getting continuous fluctuations (in the form of sinusoidal waves) for lift and pitching moment coefficient values .
Any idea where am I lagging .
Thanks

[FMDenaro]

Originally Posted by AamirSultan

Hello Everyone , Hope you are doing fine .
I am running a 2D analysis of flow over an airfoil at Re Number=10^5
I am running a steady state , density based solver simulation of the case .
At higher angle of attacks >= 10 degrees , I am getting continuous fluctuations (in the form of sinusoidal waves) for lift and pitching moment coefficient values .
Any idea where am I lagging .
Thanks

Simply, this flow problem does not have a steady state in deterministic sense. Use a time-dependent solver and perform a time averaging.
In a more rigorous approach, you 2D flow problem cna have a statistically steady state that you can try to reach using the RANS equations.

[AamirSultan]

Originally Posted by FMDenaro

Simply, this flow problem does not have a steady state in deterministic sense. Use a time-dependent solver and perform a time averaging.
In a more rigorous approach, you 2D flow problem cna have a statistically steady state that you can try to reach using the RANS equations.

Thank you so much for a concise and clear answer.
Actually I have to make Cl vs Alpha plot , so I am confuse that which value of lift coefficient should I use , as the values will be changing with time and I will have multiple values of lift coefficients at the end .

Another Question: I can calculate the time step size using Courant number and value of smallest cell size .
but How many iterations per time step should I choose .

I am a beginner and my questions may seem very basic to you so I am apologizing in advance .

Thanks again.