Experimental Investigation Of The Mechanism Of Riblet Surface Drag Reduction In Turbulent Boundary Layer

In this paper, the measurement technique of constant temperature anemometry, is used to carry out experimental study on the mechanism of riblet surface drag reduction on the turbulent boundary layer of riblet surface in wind tunnel. In the present experiment, time sequence of longitudinal velocity component and normal velocity component over riblet surface and smooth surface, along different normal positions on turbulent boundary layer which is controlled by a V-grooved plate and a flat-plate side by side in the wind tunnel has been finely measured by IFA300 constant temperature anemometer with resolution higher than Kolmogorov scale, together with single-hot-wire-sensor probe,double-hot-wire-sensor probe.The riblet surface plate and smooth surface plate experimental model is blowed with six Reynold's numbers(free stream velocities) in wind tunnel. The mean velocity profile on the turbulent boundary layer on different surfaces has been finely measured with single-hot-wire-sensor probe. Accounting of the relation of the logarithmic law of mean velocity profile and skin friction velocity, fluid viscosity coefficient etc. inner scale physics quantities the relation of skin friction velocity and skin friction shear stress,the turbulent skin friction drag and skin friction coefficient are measured with the method of mean velocity profile, by nonlinear iterating to fit the skin friction coefficient u ?.The characteristics of riblet surface drag reduction are investigated comparatively, providing experimental foundations for acquainting the mechanism of riblet surface drag reduction more.It is employed that the coherent structures and bursts are identified by multi-scale wavelet coefficient of stream velocity component signal. The time scales of multi-scale turbulent structures are defined by self-correlation method.Phased-average waveforms for longitudinal and normal fluctuation velocity, as well as Reynolds stress of multi-scale coherent eddy structures in turbulent boundary layer are extracted by the conditional sampling technique and phased-average technique.The dynamic development and evolvement course of longitudinal and normal fluctuation velocity, as well as Reynolds stress of wall turbulence multi-scale coherent eddy structures burst is studied.The characteristics for example the durative period, energy distribution and conditional phased-average waveforms of multi-scale ingredients of coherent structure on riblet surface and smooth surface flat turbulent boundary layer are analysed. The statistical mean characteristics of multi-scale coherent structure on riblet surface and smooth surface flat turbulent boundary layer are compared detailedly. The mechanism of V-grooved riblet surface turbulent boundary layer drag reduction is investigated by controlling multi-scale coherent structures.