not convergence in high angle of attack in low reynold number
 

why at the angle of attack iof airfoil s increased in the range of 10 degrees, iteration does not converge, but at a low angle of attack 0 to 8 degrees, to achieve convergence, I use the segregated solver, implicit, and K-W turbulence models, why can not achieve convergence. where lies the fault .. I put the inlet velocity boundary conditions of 2.5m / s, and the chord length 1m. help me..

Take a look at your residuals, you will probably notice that they are large and unsteady on the upper aft portion of your airfoil, and you'll probably have some unsteady shedding behaviour as well that will cause high residuals in the wake.

At high angles of attack, there isn't really a physically meaningful 'steady-state' for you to converge to, the physically meaningful solution is unsteady.