Hi , I'm running an airfoil flow simulation in FLUENT. I managed to get a good agreement with the experimental results for the lift coefficients but the drag coefficient differs alot. Is there a way to correct this?

Cheerios Rif

Typically this is an indication of poor resolution of the viscous boundary layer or a problem with the computation of the viscous contribution to the drag. Look at those two areas.

You can look for the materials of AIAA Drag Prediction workshops to find out what do you need to predict drag correctly - there are plenty of recommendations on grid resolution, turbulence models and etc.

[Ortherion]

Actually, I'm looking for a solution to this problem too. I don't think AIAA could report would be any help, in my case I've been following numerous advices, tutorials, various models and settings], all that kind of stuff, still, my Drag coefficient is ALWAYS 10x bigger than it should be according to experimental data. [even in negative values a few times ]. I think I got best results when I copied A PROCEDURE FOR NUMERICALLY ANALYZING AIRFOILS AND WING SECTIONS simulation, Cl error was 5%, Cd 600%

[agd]

As stated, this is usually an indication of a screwed-up representation of the viscous effects or the boundary layer. What is the maximum y+ of the first grid point off the airfoil surface? What turbulence model are you running? Do you even need a turbulence model? Are you resolving the boundary layer correctly?