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Q: RN at NACA23012 Full Scale Wind Tunnel Data

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Old   February 11, 2013, 21:10
Default Q: RN at NACA23012 Full Scale Wind Tunnel Data
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Derek Kim
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Hello

I am trying to simulate NACA23012 with Fluent and found NACA23012 wind tunnel report.

Its last page which has the tables of Full Scale Wind tunnel data of the airfoil has been enclosed here.

My question is why the tables have two different Reynolds Number for Zero Lift and Max. lift respectively.

In my point of view, Reynolds Number and Velocity should be constant and the dimensionless values like Cl, Cd depend on angle of attack, don't they?

As you can see, the lift coefficient varies with AoA in the tables but what is RN that I should consider for the simulation?

For your reference, the information of the report is like below.
(Sorry, I can't upload the file here due to the size limitation).

Report No. 530
Characteristics of the N.A.C.A. 23012 Airfoil from tests in the full-scale and Variable-density tunnels
by Eastman N. Jacobs and William C. Clay,
March 1, 1935.
Attached Images
File Type: jpg NACA23012 wind tunnel report.jpg (85.8 KB, 6 views)
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Old   February 12, 2013, 00:23
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Martin Hegedus
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Yikes, your comparisons may not be as straight forward as you are hoping...

The tunnel you are referring to is the full scale one with an open section. Somewhere in that section they are measuring the dynamic pressure and the measurement is affected by the angle of attack of the wing. The data is then corrected for various things. You may want to read the reports describing the tunnels and corrections before you continue...

Try NACA-TR-478, "Experimental verification of the theory of wind-tunnel boundary interference" and the references mentioned in 530.
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Old   February 12, 2013, 02:23
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Quote:
Originally Posted by Martin Hegedus View Post
Yikes, your comparisons may not be as straight forward as you are hoping...

The tunnel you are referring to is the full scale one with an open section. Somewhere in that section they are measuring the dynamic pressure and the measurement is affected by the angle of attack of the wing. The data is then corrected for various things. You may want to read the reports describing the tunnels and corrections before you continue...

Try NACA-TR-478, "Experimental verification of the theory of wind-tunnel boundary interference" and the references mentioned in 530.
Hi, Martin

Thank you for your reply.
However, I can't catch your point.

I attached three files here and two of them are the tabulated test results in the report and the other one is the result graph summarized from one of the tabulated results, Table VI.
In the file, I added a red circle in order to show you the different reynolds numbers.
In the fig 4, the numbers are 3,199,000 for C_Lmax and 3,362,000 for C_Dmin, separately.

Depending on the purpose, the RN could be a variable. but, at least here, I think the variable is the Angle of attack and the RN should be constant. Why was the number changed during the test?

Because of that, I can't make the number constant in simulating the airfoil with Fluent.

Even though I read the report completely, there was not a reason for its change in the report. T-T

Please share your idea,

Have a good day!
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Old   February 12, 2013, 02:48
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Martin Hegedus
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The velocity will not be constant because of blockage due to angle of attack. Also, I gather, the actual velocity measurement may be very uncertain because it is an open tunnel. The uncertainties are probably not explicitly stated in that report, you must read the references. This tunnel was built either in the late 20s or early 30s. The Re was not intentionally changed, they just did the best they could in determining it with what they had. The technology does not represent today's standard. Also, a 2D airfoil was not tested. Instead a 3D wing was tested and the results were corrected to an infinity aspect ratio. It may be challenging to compare CFD to these results. However, being off on the Re may not represent much uncertainty. The Re can just be linearly interpolated between CLmax and CL0. That's close enough. It is the tunnel "walls", or lack of, and the wing aspect ratio which will cause the biggest uncertainty

The following references should be read:
http://hdl.handle.net/2060/19930091534 (NACA-TR-459)
And
http://hdl.handle.net/2060/19930091552 (NACA-TR-478)
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Old   February 12, 2013, 03:18
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From the concluding remarks of 478:

"The loss in total head seems to account for the greater part of the q correction. Quite evidently the pattern, or wake of the body, is carried around the tunnel."

So, the higher the CL, the higher the head loss, the lower the q, the lower the velocity, and, therefore, lower the Re.
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Old   February 12, 2013, 19:55
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Derek Kim
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Originally Posted by Martin Hegedus View Post
The velocity will not be constant because of blockage due to angle of attack. Also, I gather, the actual velocity measurement may be very uncertain because it is an open tunnel. The uncertainties are probably not explicitly stated in that report, you must read the references. This tunnel was built either in the late 20s or early 30s. The Re was not intentionally changed, they just did the best they could in determining it with what they had. The technology does not represent today's standard. Also, a 2D airfoil was not tested. Instead a 3D wing was tested and the results were corrected to an infinity aspect ratio. It may be challenging to compare CFD to these results. However, being off on the Re may not represent much uncertainty. The Re can just be linearly interpolated between CLmax and CL0. That's close enough. It is the tunnel "walls", or lack of, and the wing aspect ratio which will cause the biggest uncertainty

The following references should be read:
http://hdl.handle.net/2060/19930091534 (NACA-TR-459)
And
http://hdl.handle.net/2060/19930091552 (NACA-TR-478)
Hello, Martin

Thank you very much for your kind explanation.
It is really helpful enough and I'm reading the references.
thank you for that.

Have a good day!
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