Incorrect Drag Coefficients
 

Hi,
I'm a third year MechEng student and I'm having difficulties with some CFD analysis.
I am currently meshing an aerofoil in ICEM, and modelling in CFX at various angles of attack.

My lift coefficients are coming out with errors between 3% and 10%, which I'm ok with.
My drag coefficients however are producing errors between 55% and 80%, which is obviously not good.

So far I've tried re-fining my mesh, playing with the surface roughness of the aerofoil, trying different turbulence models.

I have attached a few of screenshots of my mesh, however I'm quite confident its alright because of my correct lift coefficients.

Any help would be greatly appreciated.
Thanks
Will

Attachment 7106

Attachment 7107

Attachment 7108

Apologies for the double post, the forum said the first post didnt work.
Can I delete one of them?

I have the same problem too.however in drag coefficient ,you'll try to use only pressure drag (not total drag ). In my view CFD can predict viscous force better than measurement which is usually hard to estimation, then CFD give the high value than experimental value in low angle of attack range.

hope this help