Effect of local forcing on a turbulent boundary layer

An experimental study is performed to analyze flow structures behind local suction and blowing in a flat-plate turbulent boundary layer. The local for cing is given to the boundary layer flow by means of a sinusoidally oscilla ting jet issuing from a thin spanwise slot at the wall. The Reynolds number based on the momentum thickness is about Re-0 = 1700. The effects of local forcing are scrutinized by altering the forcing frequency (0.011 less than or equal to f(+) less than or equal to 0.044). The forcing amplitude is fi xed at A(0) = 0.4. It is found that a small local forcing reduces the skin friction and the skin friction reduction increases with the forcing frequen cy. A phase-averaging technique is employed to capture the large-scale vort ex evolution. An organized spanwise vortical structure is generated by the local forcing. The cross-sectional area of vortex and the time fraction of vortex are examined by changing the forcing frequency. An investigation of the random fluctuation components reveals that turbulent energy is concentr ated near the center of vortical structures.