# Reference Values

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 May 13, 2012, 10:06 Reference Values #1 Member   nazareno mancinelli Join Date: Mar 2009 Location: argentina Posts: 35 Rep Power: 10 hi. i'm simulatig a 2D( 2ddp double precision solver) airfoil (naca0021). the chord lengh (was made up using gambit) is 0.14m. my problem is to correct set up the "Reference Values" to match the results with the published one (cd=0,019 cl=0,85) A=0.14 cd=0,135-----cl=0,85 A=1 cd=0,019-----cl=0,1119 as you can see, if i set the reference area = 0.14, i have a correct solution for lift, but wrong with the drag. whereas i set the reference area =1, i have a good drag, but a wrong lift what its wrong here? whats i'm doing wrong? it is not possible to solve a problem with a chord lenght that is not = 1? i thought i would not be a big problem to change it to 14cm can anyone help me? thanks in advance

May 13, 2012, 17:42
#2
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Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
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Quote:
 Originally Posted by yochule hi. i'm simulatig a 2D( 2ddp double precision solver) airfoil (naca0021). the chord lengh (was made up using gambit) is 0.14m. my problem is to correct set up the "Reference Values" to match the results with the published one (cd=0,019 cl=0,85)
you should use the same definition for each coeficient as the published result. what reference area did they use for drag and lift? the same or different references?

For airfoils, typically the reference area is the planform area which is sometimes equivalent to the chord length, keeping in mind this also changes with angle of attack.

 May 13, 2012, 17:49 #3 Member   nazareno mancinelli Join Date: Mar 2009 Location: argentina Posts: 35 Rep Power: 10 agree with that (the references its the chord lengh). but the problem here is that (lets say) with the chord lengh as reference area in the reference value pannel, i do have a good result for cl, but the cd its wrong. can you get the point here?

May 13, 2012, 17:52
#4
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Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 2,019
Rep Power: 27
Quote:
 Originally Posted by yochule agree with that (the references its the chord lengh). but the problem here is that (lets say) with the chord lengh as reference area in the reference value pannel, i do have a good result for cl, but the cd its wrong. can you get the point here?
if it's wrong then it's wrong, what can I do?

 August 4, 2017, 18:27 #5 New Member   Thusitha Join Date: Aug 2016 Location: UK Posts: 6 Rep Power: 3 Out of interest, did you managed to solve the problem?

 Tags airfoil, drag coefficient, lift coefficient, reference values

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