Computational Fluid Dynamics (CFD) analysis of a three dimensional (3-D) National Advisory Committee for Aeronautics (NACA) 2412 airfoil was compared with same dimensional 3-D NACA 2412 with internal passage. The computational domain was composed of 2109509 elements for NACA 2412 and 2258962 elements for NACA 2412 with internal passage. Calculations were done for various Mach numbers by varying the angle of attack constant for above mentioned turbulence model. The flow patterns were studied by solving the steady-state governing equations of continuity and momentum conservation combined with turbulence Spalart-Allmaras model. The objective of the study was to compare flow separation location and characteristics for the NACA 2412 and NACA 2412 with internal passage. From the results, we observe that as the angle of attack increases, the value of lift coefficient also increases which in turn implies increase in lift force. When we compare the lift coefficient for 3D NACA 2412 airfoil and 3D NACA 2412 airfoil with internal passage, we can observe that value of lift coefficient is higher for 3D NACA 2412 airfoil with internal passage at high angle of attack and at higher free stream velocities. From the comparison of the pattern of streamlines for 3D NACA 2412 airfoil and 3D NACA 2412 airfoil with internal passage, we can conclude that point of separation for 3D NACA 2412 airfoil with internal passage is shifted towards trailing edge. This reduces the boundary layer separation at higher angle of attack from the airfoil.