It is shown how well-chosen perforations in a wall flow can locally reduce skin friction drag by modifying the generation of bursts in the boundary layer. For this purpose, a detailed hot wire experimental boundary layer investigation of the flow past a perforated plate, complemented with large eddy simulations, is carried out and compared to the smooth baseline. The perforated plate is obtained with an array of flush-mounted circular cavities. These cavities are disposed in a periodic staggered arrangement. For the three tested flow velocities, the momentum thickness based Reynolds number varies from 1830 to 3380 and the cavity diameter and spacing in wall units respectively from 130 to 250 and 587 to 1075, the latter being identical in both spanwise and streamwise directions. The mean velocity profiles evidence a thickening of the viscous sublayer and a decrease of the friction velocity as compared to the smooth wall case. The application of the Variable Interval Time Averaging (VITA) technique highlights an upward shift of the bursts from the wall and an attenuation of the average burst intensity and duration.Spanwise measurements evidence an overall bursts attenuation despite the lack of spanwise uniformity.The 3D mean flow topology arising from the large eddy simulations provides evidences of the qualitative similarities between the current setup and the spanwise wall oscillations.

Two separate experimental campaigns of a spatially developing turbulent boundary layer under approximately zero-pressure-gradient at moderate Reynolds numbers ($1700<Re_{\theta} < 3400$) are conducted with stereoscopic Particle Image Velocimetry and one component Hot Wire Anemometry. This range of Reynolds numbers is found to be of particular interest for turbulent boundary layer control investigations.The motivations behind this work rely on the lack of recent studies which provide a rigorous experimental database on a flat plate turbulent boundary layer, openly available online. This is critical as, in most of the cases, the modification of the statistics resulting from turbulent boundary layer control strategies are compared with a smooth baseline reference.The statistics of the velocity fields, obtained with the two techniques, show a good match with the Direct Numerical Simulation in literature results. We focused on the skin friction evaluation by means of Clauser's chart technique.The near wall turbulence activity and the associated coherent structures are investigated by means of the Variable Interval Time Averaging technique using the hot wire signal. The influence of the acquisition and algorithm parameters as well as the effect of the Reynolds number are reported. The logarithmic and outer structures are investigated by applying the Uniform Momentum Zones technique to the PIV data-set. The hierarchical distribution of the uniform momentum zones as a function of the the wall distance as well as their variation with the Reynolds number confirm the validity of the Attached Eddy Model even at the moderate Reynolds numbers of the current investigation.

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