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 yochule May 13, 2012 10:06

Reference Values

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

 LuckyTran May 13, 2012 17:42

Quote:
 Originally Posted by yochule (Post 360803) 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.

 yochule May 13, 2012 17:49

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?

 LuckyTran May 13, 2012 17:52

Quote:
 Originally Posted by yochule (Post 360850) 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?

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