# Converting 3-D NACA Wind tunnel test data to 2-D data

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 August 5, 2014, 08:50 Converting 3-D NACA Wind tunnel test data to 2-D data #1 New Member   M. Abdul Akbar Join Date: Feb 2013 Posts: 19 Rep Power: 13 Hi, For the purposes of my work, I need to get lift and drag coefficients of certain NACA airfoils for certain Reynolds Number's. However, the constraints of the wind tunnel at my lab does not permit a 2-D (infinite span) test. I can only fit a smaller sized specimen which will inevitably lead to 3-D effect by vortices at the ends. My questions is, how can I convert the 3-D (finite span) lift and drag coefficients obtained from the wind tunnel test to a 2-D (infinite span) ????. Please excuse my ignorance on aerodynamics. Thanks in advance.

 August 5, 2014, 10:43 #2 Senior Member   Troy Snyder Join Date: Jul 2009 Location: Akron, OH Posts: 219 Rep Power: 18 It may be possible to reduce the vortex induced drag by fitting your 3d experimental airfoil with winglets. The results should then compare better with 2d data.

 August 5, 2014, 11:11 #3 Member   Join Date: Dec 2012 Posts: 92 Rep Power: 13 In our university they just mount the wing between two walls. According to Helmholtz a vortex can end on a wall and you get rid of the wind tip vortex. If you can't do that you can calculate back from your wing with the theory for induced drag to a 2D-wing. This works as well but is obviously more error prone and more work.

 August 5, 2014, 21:55 #4 New Member   M. Abdul Akbar Join Date: Feb 2013 Posts: 19 Rep Power: 13 Thanks for the replies. Hi Beer, I hope you mean the correction calculations as shown in this page, right ??? http://people.rit.edu/pnveme/EMEM682n/review/liftcoeff.html When you say it is error prone, do you mean to say that it is more prone to calculation mistakes or that the results may be inaccurate. If it is about the results being inaccurate, do you have any idea of how much the results may vary from the actual ??? Thanks in advance

 August 5, 2014, 23:27 #5 Member   Join Date: Dec 2012 Posts: 92 Rep Power: 13 Hi The page shows pretty much what I meant to say, but not exactly. What you want to know is the red arrow called L in the picture of the wing with the forces. It is the "real" lift force which is rotated by the wing vortex. If you merge the equations for lift and drag (0 degree and induces drag) you can find a correction factor for the lift coefficient not just for the lift coefficient slope. To your question: both. But I assume you are able to calculate that problem without making mistakes there. What I meant is error prone can be seen at the end of the page. A wing is almost never perfectly elliptic. So you have to guess, measure or calculate the Oswald factor. There are some good approximation (I remember using them at uni) for differently shaped wings based on empirical equations. I think the error of these should be small because the equations are approved by the FAA, at least AFAIK. One other remark: I just read through your first question again. The fact that you use NACA can help you solve your problem. You can try to find lift and drag data on the internet and compare it to your experimentally generated and corrected data to see if your calculations are right.

 Tags drag, finite span, infinite span, lift, wind tunnel