Experimental Investigation Of Coherent Structures Influenced By Periodic Blow-suction Disturbance In Turbulent Boundary Layer

An experiment is performed to study multi-scale coherent structure in turbulent boundary layer, which is controlled by periodic blowing and suction disturbance with different frequencies over a flat-plate in the wind tunnel.A periodic local blowing/suction forcing produced by a woof with different frequency from a 5mm thin latitudinal slot on the flat is introduced to alter multi-scale characters of coherent eddy structure, such as occurring probability, turbulent intensity, energy distribution, phased-averaged waveform.Time sequence of longitudinal velocity component and normal velocity component within and without different periodic blow-suction disturbance along different longitudinal and normal positions have been finely measured by IFA300 constant temperature anemometer with high resolution. The method of Fast Fourier Transform Algorithm (FFT) has been used to extract the region containing the disturbance signal, to confirm the field where the disturbance has influence.The phased-average waveforms for longitudinal and normal fluctuating velocity components are studied from the view of Reynolds-stress in the process of eject and sweep, and the phase relationship between them. It is found out that the amplitude, durative period of phased-average waveforms for ejecting and sweeping, the phase difference of the longitudinal velocity component and normal velocity component have been changed by the periodic disturbance, the drag reduction is obtained in local region.