Abstract
When the periodic velocity fluctuation is introduced in a mean flow, the separation flow changes in various manners. This report concerns with the "flapping" motion of the separation shear layer by means of the phase averaging of instantaneous velocity fields over the separation region. In order to know the principal motion of the velocity field precisely, wavelet transform is used. The shapes of contour are quite different at each phase and with the frequency of the fluctuation. The separation shear layer is depressed and pulled up with the fluctuating of the velocity in the mean flow. And when the suitable frequency was chosen the separation region disappeared at the phase of depression.
