Direct numerical simulations (DNS) of the flow dynamics over a NACA 0012 airfoil at Reynolds number Re = 5×104 at different angles of attack are presented. The dynamic of the large separation bubble, characterised by laminar boundary layer separation, transition to turbulence and flow reattachment is analysed in detail by means of instantaneous data al different locations in the suction side of the airfoil. It is found that LSB behaviour is characterised by a low-frequency with a time scale much larger than of the vortex shedding. Thus, in order to capture all the time scales of the flow, statistical results presented have been integrated during a sufficient long time.