Experimental Investigation Of Multi-scale Coherent Structures Controlled By Periodic Blow-Suction Disturbance On Wall Turbulence

In this paper, the technique of constant temperature anemometer is usedto study the turbulent boundary layer which is controlled by periodicblow-suction on the wall.In the present experiment, the time sequence of longitudinal velocitycomponent within different periodic blow-suction and withoutblow-suction, along different normal positions in a flat-plate turbulentboundary layer has been finely measured by IFA300 constant temperatureanemometer with resolution higher than Kolmogorov scale. The scales ofmulti-scale eddy structures are determined by self-correlation function. Itis represented that the coherent structures and intermittency are identifiedby multi-scale flatness factor based on locally averaged velocity structurefunctions. Phased-average evolution shapes for multi-scale coherent eddystructures in turbulent boundary layer are extracted by this conditionalsampling technique. The dynamic course of multi-scale coherent eddystructures'bursting is researched.A periodic blowing/suction forcing, issued from a thin latitudinal slot onthe wall, is introduced to alter multi-scale ingredients of coherent eddystructure and their energy distribution in turbulent boundary layer, what ismore, to perturb and control the coherent eddy structures in order toaccomplish drag reduction of skin friction.It is found that within periodic suction, the viscous sublayer is incrassateand the buffer layer is attenuation even disappears near the wall region;the log-law region moves upwards, the coherent structures are obviouslyrestrained and also the flow trends to be laminar flow. The resistance isdecreased. In the log-law region and even further away from the wallregion, the locally periodic suction has no effect on the flow structures.