[didiean]

Hello, everyone!
My English is not very good, hope I can describe my problems clearly.
I am trying to do some simulation on deformation of an airfoil, before that, I tried to test validity of Fluent on 2D airfoil which I thought would have no trouble. BUT, I have got big troubles.
Here are my cases, and the outside of the flowfield is about 50 chord length listed as following pictures. The airfoil has sharp trailing edge with no length, so I try to construct a C-grid. The Reynolds number is 2 million.
First, I used velocity-inlet and outflow as boundary conditions. But the lift coefficients are about or even more than 10% less than the experiments using SA and other full turbulence models. For transitional SST models, the residuals and lift coefficient are quite unstable, and I am not sure it's the convergent results even its results are more accurate for the experiment.
Then I used pressure-far-field as boundary conditions. But it is not easy for me to get a convergent results. Most of the time, the residuals are varying at about 0.1 or 1 order, and the lift coefficients are varying.

I doubt maybe my mesh is too poor. So I try my best to get better meshes. But it doesn't work. Check the mesh quality with gambit, the biggest EquiSize skew is about 0.479, and the biggest aspect ratio is about 589 near the airfoil. (Wall plus <1) . Check the mesh quality with Fluent 12, the maximum cell squish is about 0.59.

What other parameters should I check ? Which aspect can I improve my grid? Or what set should I do for fluent？
It is driving me crazy~ I ever thought Fluent could simulate the lift coefficients of airfoil under moderate angles of attack~ And someone simulates blunt airfoil using O-grid whose cell squish is about 0.74 and biggest EquiSize skew is 0.54, can get convergent results quite easily.
I divide the flow field into several blocks, but I check the transition of different blocks very carefully, there are no sharp changes.

Any comment would be welcome~ Thank you~