Can I validate results from a different aerofoil?

jetaji1 · March 5, 2022, 18:18

Hi,

I am running CFD simulations on a NACA 0012 aerofoil profile with a plain flap, 80% chord length from the leading edge. I was trying to look for a good validation paper that has wind tunnel tests and have been struggling.

However, I found a paper (linked below) from NASA that investigates a plain flap at similar flow conditions and chord length but is conducted on a NACA 23012 aerofoil. Would I be able to use this paper to validate my results and state the discrepancies due to the different aerofoil?

If not, does anyone have any other way to validate my results?

N.b. Verification has been completed.
N.b. Link: https://ntrs.nasa.gov/api/citations/...9720006329.pdf

OR Title: WIND-TUNNEL STUDY OF SLOT SPOILERS
FOR DIRECT LIFT CONTROL by Dominick Andrisani II, Garl L. Gentry, Jr., and Joseph W. Stickle.

agd · March 8, 2022, 09:18

Well, consider the following. You are solving a set of partial differential equations whose solutions depend entirely on the boundary conditions, and you are asking whether you can use the solution based on one set of boundary conditions (i.e. the contour of the airfoil) to validate a solution using a different set of boundary conditions (different contour). So if you are asking if you can do a one-to-one comparison, then the answer is no.

Validation is not an easy task. What you may be able to do is actually run the case that you have data for (the NACA 2312 with flap). Use that to gain some confidence in your solver. If you do a good job with that, then you can at least have some confidence in the original solution.

joshwilliams · March 8, 2022, 10:04

I agree with agd. Experimental data is usually sparse and hard to come by for many applications. It is best to use the exact same setup (in this case, use the NACA 23012 with flap geometry). Then, once you get good agreement with experiments and have confidence with the mathematical and numerical setup (turbulence models, mesh spacing and structure, time discretisation resolution and schemes), then you can apply it to cases you do not have experimental data for (your NACA 0012).

In cases without experimental data, you should always at least exercise good practices such as mesh sensitivity tests to ensure results are robust and reliable.

fluid23 · March 14, 2022, 11:07

I would add to this that symmetric airfoils are notoriously more difficult to validate and the 0012 in particular has historical data sets that do not agree with each other. Deciding which is 'correct' can be a real challenge.

Unless you are married to the 0012, the 23012 is a better choice for a validation exercise IMO.

March 5, 2022, 18:18	Can I validate results from a different aerofoil?	#1
jetaji1 New Member JetT Join Date: Jan 2021 Posts: 4 Rep Power: 5	Hi, I am running CFD simulations on a NACA 0012 aerofoil profile with a plain flap, 80% chord length from the leading edge. I was trying to look for a good validation paper that has wind tunnel tests and have been struggling. However, I found a paper (linked below) from NASA that investigates a plain flap at similar flow conditions and chord length but is conducted on a NACA 23012 aerofoil. Would I be able to use this paper to validate my results and state the discrepancies due to the different aerofoil? If not, does anyone have any other way to validate my results? N.b. Verification has been completed. N.b. Link: https://ntrs.nasa.gov/api/citations/...9720006329.pdf OR Title: WIND-TUNNEL STUDY OF SLOT SPOILERS FOR DIRECT LIFT CONTROL by Dominick Andrisani II, Garl L. Gentry, Jr., and Joseph W. Stickle.

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March 8, 2022, 09:18		#2
agd Senior Member Join Date: Jul 2009 Posts: 351 Rep Power: 18	Well, consider the following. You are solving a set of partial differential equations whose solutions depend entirely on the boundary conditions, and you are asking whether you can use the solution based on one set of boundary conditions (i.e. the contour of the airfoil) to validate a solution using a different set of boundary conditions (different contour). So if you are asking if you can do a one-to-one comparison, then the answer is no. Validation is not an easy task. What you may be able to do is actually run the case that you have data for (the NACA 2312 with flap). Use that to gain some confidence in your solver. If you do a good job with that, then you can at least have some confidence in the original solution.

March 8, 2022, 10:04		#3
joshwilliams Senior Member Josh Williams Join Date: Feb 2021 Location: Scotland Posts: 112 Rep Power: 5	I agree with agd. Experimental data is usually sparse and hard to come by for many applications. It is best to use the exact same setup (in this case, use the NACA 23012 with flap geometry). Then, once you get good agreement with experiments and have confidence with the mathematical and numerical setup (turbulence models, mesh spacing and structure, time discretisation resolution and schemes), then you can apply it to cases you do not have experimental data for (your NACA 0012). In cases without experimental data, you should always at least exercise good practices such as mesh sensitivity tests to ensure results are robust and reliable.

March 14, 2022, 11:07		#4
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	I would add to this that symmetric airfoils are notoriously more difficult to validate and the 0012 in particular has historical data sets that do not agree with each other. Deciding which is 'correct' can be a real challenge. Unless you are married to the 0012, the 23012 is a better choice for a validation exercise IMO.