An unsteady numerical simulation was performed to analyze flow structure behind a local suction/blowing in a flat-plate turbulent boundary layer. The local forcing was given to the boundary layer flow by means of a sinusoidally oscillating jet. A version of the unsteady k-epsilon -f(mu) model [Fluid Dyn. Res. 26 (6) (2000) 421] was employed. The Reynolds number based on the momentum thickness was about Re-theta = 1700. The forcing frequency was varied in the range 0.011 less than or equal to f(+) less than or equal to 0.044 with a fixed forcing amplitude A(o) = 0.4. The predicted results were compared and validated with the experimental data. It was shown that the unsteady locally forced boundary layer flow is predicted well by the k-epsilon -f(mu) model. The time-dependent numerical flow visualizations were demonstrated during one period of the local forcing. The effect of the pitch angle of local forcing on the reduction of skin friction was examined. (C) 2001 Elsevier Science Inc. All rights reserved.