No steady solution for airfoil at high AoA

NonStopEagle · January 17, 2020, 16:11

Hey guys,
I am trying to simulate a NACA 0015 airfoil at high AoA (about 16 degrees)
I am getting oscillating cl and cd values when I run a steady simulation.
Upon switching to an unsteady simulation, for very small time steps( of the order 1e-5) the cl and cd values become constant, but are incorrect. When I increase the timestep ( to about 1s or 2s) the oscillating behavior of cl and cd plots returns.
How do I get convergence?

NonStopEagle

AidealZohary · March 3, 2021, 16:52

Hi, I did not use NACA 0015 and at a high AOA. But I do know that the stability of the unsteady simulation is also important. I outlined some steps that I did to get around it. Perhaps can be helpful. Take a look:

Numerical Investigation on the Pressure Drag of Some Low-Speed Airfoils for UAV Application.

Unsteady 3-equation k omega intermittency SST was used. Good comparison with XFOIL and experimental data. Transition features also shown through cf and cp plots.

January 17, 2020, 16:11	No steady solution for airfoil at high AoA	#1
NonStopEagle New Member Join Date: Sep 2019 Posts: 24 Rep Power: 7	Hey guys, I am trying to simulate a NACA 0015 airfoil at high AoA (about 16 degrees) I am getting oscillating cl and cd values when I run a steady simulation. Upon switching to an unsteady simulation, for very small time steps( of the order 1e-5) the cl and cd values become constant, but are incorrect. When I increase the timestep ( to about 1s or 2s) the oscillating behavior of cl and cd plots returns. How do I get convergence? NonStopEagle

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March 3, 2021, 16:52		#2
AidealZohary New Member Aideal Zohary Join Date: Feb 2019 Location: Malaysia Posts: 28 Rep Power: 7	Hi, I did not use NACA 0015 and at a high AOA. But I do know that the stability of the unsteady simulation is also important. I outlined some steps that I did to get around it. Perhaps can be helpful. Take a look: Numerical Investigation on the Pressure Drag of Some Low-Speed Airfoils for UAV Application. Unsteady 3-equation k omega intermittency SST was used. Good comparison with XFOIL and experimental data. Transition features also shown through cf and cp plots.