Incoherent values of Cl in 2D calculation
 

Hi there,

I'm blowing my mind on a Fluent problem. I've done some calculations on an airfoil with and without an airbrake. I gave up the 3D because I had some strange results (like 25% more lift with the airbrake up !).

So I made my 2D model using Catia, meshed with gambit, and processed with Fluent. The residuals are converging in like 1200 iterations. But for 1m² of my naked, 1m chord, FX66 airfoil, I get some impossible results :
- Drag : 8.69 N
- Lift : 608.41 N

That gives me 70 lift to drag ratio instead of a normal 25 for this airfoil. I wouldn't mind to have like too much or too few lift AND drag because I know it's a reference value thing, but in that case this is the drag to lift ratio which is not possible.
I tried changing things in the reference values but the Force reports is still exactly similar. It's even more frustrating that my flow looks nice.

http://img830.imageshack.us/i/airfoil.jpg/http://img830.imageshack.us/i/airfoil.jpg/

Did any of you encounter such a problem ? Do you have a clue for the solution ?

Thanks, greetings from France
Charles

I might have a clue.
I used a Size function to refine the mesh around the airfoil in Gambit. Is that regular in 2D ? I tried to compute this airfoil using basic "Tri" element without any refining and I get a 11 lift to drag ratio which is plausible at a 0° angle of attack.

If the size function is not appropriate in 2D and is the source of my problem ? What would you recommand to mesh my boundary layer ?

Thanks
Charles