# Drag coefficient do not match of the experimental result

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December 5, 2018, 15:13
Drag coefficient do not match of the experimental result
#1
New Member

kaan
Join Date: Nov 2018
Posts: 7
Rep Power: 7
Hi i have a problem to my naca0012 airfoil (2d) analysis. I set the reference values, boundary conditions and i solve this with k-omega method but i get confused because of drag coefficient. im trying to match my values to experimental values(nasa's thesis) and i didnt. lift coefficient is excatly match but drag is not. what is the solution of this error(or whatever)?

mesh element number:40000

Thats my values

Thats Experimental Values

Model

Method

Reference Values

Pressure Farfield b.c

Also initial values (i computed from farfield)

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 December 5, 2018, 16:01 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,680 Rep Power: 66 Drop the coefficients and try comparing the forces in units of N.

December 6, 2018, 06:53
#3
New Member

kaan
Join Date: Nov 2018
Posts: 7
Rep Power: 7
Quote:
 Originally Posted by LuckyTran Drop the coefficients and try comparing the forces in units of N.
drop the coefficients? i didnt get it and forces dont matter on my problem i interested in coefficient also i have not force values to compare forces? Am i misunderstand about forces? Thx for comment btw.

Last edited by recep911234; December 6, 2018 at 11:44.

 December 12, 2018, 18:02 #4 New Member   kaan Join Date: Nov 2018 Posts: 7 Rep Power: 7 any help???

 December 12, 2018, 18:07 #5 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,680 Rep Power: 66 If one coefficient matches and not the other, usually it's because one of the coefficients is using different reference values than the other. That's why it's a good idea to forget about the coefficients altogether and compare raw forces (N) to forces (N) even if it means you have to back-calculate some parameters. Also you might find that you're unable to convert from the coefficients back to the force because something is missing in the publication or maybe you just don't know what you are doing. It is always a good idea to do some basic calculations.

 December 12, 2018, 23:54 Please cross check the values of turbulence and pressure #6 New Member   sree charan teja Join Date: Oct 2018 Posts: 8 Rep Power: 7 note: cross check the values of turbulence, try using k epsilon and at boundary conditions check the turbulence intensity (usually 5 % as turbulence intensity in default.) use analytical formula and find the corresponding values before using them. cross check the pressure at the boundary condition, it should be in corresponding with the gauge pressure. (else you can put the gauge pressure as 0 for less confusion)

 Tags airfoil 2d, drag and lift, drag coeffcients, fluent, naca 0012