Abstract: The lift of traditional airfoil with sharp trailing edge, for which the time response course to angle of attack can be described by Wagner function, changes with angle of attack under the combined effects of the flap and slat; while for the airfoil with Internally Blown Flap (IBF), whose maximum lift is increased by means of the suppression of flow separation, the lift is effectively adjusted by the blowing jet, which can induce the change of the location of stagnation point and the airfoil circulation. Considering that it is not clear whether the time response characteristics of the lift of the airfoil with IBF are the same as those of traditional airfoils or not, this paper investigates the former in detail with the focus on the comparison between them. With the numerical method validated by the case of dual-radius circulation control airfoil with a flap deflection angle of 30°, the unsteady flow field around the subsonic airfoil with the ratio of maximum thickness to chord of 18% and IBF are numerically simulated under the effect of steady blowing and its transient features are also analyzed. The results imply that the time dependence characteristics of the lift response of the circulation control airfoil with IBF to blowing excitation have a correlation with Wagner function and can be described by using it.

Key words: lift response, circulation control, internally blown flap, time interval, jet effect