Negative angles of incidence
 

Hi everybody. I´m studying an airfoil in order to calculate lift and drag coefficients over a range of angles of incidence. The results are OK for the possitive ones, but I find some problems when calculating drag coefficients for the negative angles of incidence, like -1º and -2º. The airfoil is a supercritical one, and the boundary conditions are pressure far fiel and wall for the airfoil. Mach number is 0.76. The domain (far field) is big enough. Thanks for your help!!!!!!!