An experimental study employing LDV and PIV was performed to analyze the effect of local forcing on a turbulent boundary layer. The local forcing was introduced to the boundary layer by means of a sinusoidally-oscillating jet issuing from a thin spanwise slot on the surface. The Reynolds number based on the momentum thickness over the slot was about $Re_θ=690$. Two forcing frequency ($f^+$= 0.044 and 0.066) were chosen at a fixed forcing amplitude. Based on the longitudinal mean velocity distributions by LDV, the skin friction coefficients ($C_f$) were calculated with the computational Preston tube method. The reduction of skin friction by the local forcing was achieved, where the higher frequency forcing was more effective than the lower one. The flow visualization and the phase-averaged velocity profiles by PIV revealed that the spanwise large-scale vortices were generated at the downstream of the slot and they persisted farther downstream.
