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Drag coefficient do not match of the experimental result

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Old   December 5, 2018, 15:13
Question Drag coefficient do not match of the experimental result
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kaan
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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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Old   December 5, 2018, 16:01
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Drop the coefficients and try comparing the forces in units of N.
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Old   December 6, 2018, 06:53
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Quote:
Originally Posted by LuckyTran View Post
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.
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Old   December 12, 2018, 18:02
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any help???
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Old   December 12, 2018, 18:07
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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.
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Old   December 12, 2018, 23:54
Default Please cross check the values of turbulence and pressure
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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)
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airfoil 2d, drag and lift, drag coeffcients, fluent, naca 0012

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