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Lift and drag coefficients of the NACA 0018

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Old   September 8, 2017, 17:33
Question Lift and drag coefficients of the NACA 0018
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Volodymyr Klymko
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Hi all,

The goal of my project is to get both drag and lift coefficient of the NACA 0018.

I am using Converge and EnSight in order to get these values.

By using Converge I am able to get x,y,z components of the Force induced by the air flow. So, if I know the direction of my flow I will be able to to get Drag Force (parallel to the direction of the flow) and Lift Force (perpendicular to the direction of the flow). Then, by knowing the area of the airfoil (Span*Chord) I can easily get the drag and lift coefficient as Drag Force=0.5*rho*v^2*A*Cdrag and Lift Force=0.5*rho*v^2*A*Clift.

Could anybody let me know if flow of thoughts is correct, please?

Thank you in advance.
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Old   September 21, 2017, 15:44
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Tristan Burton
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Volodymyr,

That is correct!

Best regards,

Tristan
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Old   September 21, 2017, 16:05
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Volodymyr Klymko
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Tristan,

Thank you for your answer.

In case of 3D NACA airfoil would the calculation of the area (A=chord*span) be the same? Or It should be changed to a reference area?

Personally, I think that it should be the same, however I would like to have a professional opinion if possible.

Also, my airflow is aligned with x-direction and in order to get Drag force I am adding Pres_Force_X and and Visc_Force_X. What about Lift force? It should be only Pres_Force_Y or Pres_Force_Y + Visc_Force_Y?

Thanks.

Volodymyr.
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Old   September 22, 2017, 17:23
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Jerome Le Moine
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Volodymyr,

Be careful when dealing with 2D vs 3D, there is a difference between the 3d lift coefficient (CL) and 2d lift coefficient (Cl). Literature will usually report the 2D lift coefficient but by doing a surface integral of the wing you will find a 3D lift coefficient because it is calculated over the overall area of the wing. There is a correlation between 2D and 3D lift coefficient in function of the aspect ratio that can be found in literature. Lift is a pressure force so no viscous forces should be included in the calculation of the lift. Viscous forces comes in play when calculating the drag. For more details on these I will refer to a introduction to aerodynamics book. I hope this helps. Thanks,
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Old   September 22, 2017, 17:52
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Jerome,

Thank you so much for your reply.

I'm sorry I haven't mentioned yet that my goal is to simulate the flow over the vertical axis wind turbine and then over the counter-rotating VAWT.

I've started with NACA profile for the fist base.

So, one of the Converge's output files is a "bound(ID of the wall)-wall out", which gives the value of the wall area of my airfoil. Would this value be correct in order to get my lift and drag coefficients or it is better to use (Span*Chord)?

Thanks again for your information.
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