[MadsR]

Hi.

I get drag overprediction from CFX simulations of an 2D airfoil

Setup info:
1. I have an 2D airfoil setup in CFX
2. Mesh is created in ICEM Hexa. 200k->900k mesh dependent tests done
3. max(y+)<1
4. turbulence model is k-omega-SST
5. fully turbulent, no transition
6. angle of attacks investigated 0-15deg
7. Re is 3e6
8. domain extents sensitivity is investigated, 60chords of domain extent is found sufficient
9. butterfly/O-mesh, inlet (bottom/left)-outlet(top/right) BC's
10. high-resolution and specified blend factor of 1.0 is investigated
11. convergence to 1e-6 (max residuals) and lift/drag convergence monitored

I compare these CFX results with an academic code which has a good track record. I get less than 1% discrepancy on the lift coefficient, which is quite good. But drag (which I know is harder to resolve) is off by up to 20% (more than the academic code).

Any suggestions on what to check? Help would be greatly appreciated.

/Mads