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Fluctuations in lift and pitching moment coefficient values at higher angle of attack

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Old   December 20, 2018, 11:51
Exclamation Fluctuations in lift and pitching moment coefficient values at higher angle of attack
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Aamir Sultan
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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
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Old   December 20, 2018, 12:12
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Filippo Maria Denaro
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Quote:
Originally Posted by AamirSultan View Post
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.
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Old   December 20, 2018, 13:11
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Originally Posted by FMDenaro View Post
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.
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fluctuations, lift and drag, lift and drag calculation, lift coefficent

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