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NACA 0012 low speed validation problem

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Old   March 4, 2019, 14:46
Default NACA 0012 low speed validation problem
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Hi everyone,

I am modelling a NACA 0012 airfoil using CFX at velocity 1.15 m/s, 1.55 deg AoA in air at 20 deg C (Re = 76104), but I am having issues validating the drag coefficient at this velocity as there seems to be about a 35% error when compared to NASA validation.

The lift coefficient validates quite well.

I have been using this for validation: https://turbmodels.larc.nasa.gov/naca0012_val.html

Re for NASA validation = 6 million

Am I using the wrong validation due to these differences in Re?

Thank you!

Last edited by 35matt215; March 4, 2019 at 17:24.
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Old   March 4, 2019, 17:09
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Re = 76000 is likely to be a transitional flow, with turbulence transitional the rear half of the foil or maybe fully laminar flow. That depends on the exact airfoil, upstream conditions, surface roughness and so on.

Re = 6M is definitely fully turbulent over the whole airfoil.

They do not look like a good match to me.
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Old   March 4, 2019, 17:19
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Thanks for your reply!

So do you think it would be best if I look for papers with a smaller Re in order to validate my model with?
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Old   March 4, 2019, 18:44
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Reynolds number is probably the most fundamental parameter in fluid mechanics. If you don't match the Reynolds number then you are talking about completely different flows.

So in short, yes - you need to find data at the same Re number you are modelling.

Here is a great resource for low Re airfoils - https://m-selig.ae.illinois.edu/uiuc_lsat.html
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