Experimental Investigation of Multi-Scale Eddy Structures' Intermittency in Turbulent Flow Using Probability Density Function of Wavelet Coefficients

The longitudinal velocity component in a fully developed turbulent boundary layer was measured by IFA300 hot wire anemometer and the statistical properties were studied experimentally.The velocity time sequence at different vertical locations in the turbulent boundary layer was obtained with resolution higher than the frequency that corresponds to Kolmogorov dissipative scale.The velocity signals were analyzed by wavelet transform,which described the local relative strain distortions for multi-scale eddy structures in turbulent flows.The Extended Self-Similarity(ESS) was applied to the statistical analysis of the multi-scale wavelet coefficients.The intermittency features,studied through the probability density function of the wavelet coefficients,were found to be influenced by multi-scale coherent eddy structures and were confirmed to be dependent on the distance from the wall.The intermittency features and the probability density function were compared between before and after excluding multi-scale coherent eddy structures.It has been observed that multi-scale coherent eddy structures were responsible for the anomalous scaling law in turbulent boundary layer.When such coherent eddy structures are eliminated,intermittency anomalies are no longer observed and the Kolmogorov linear scaling prediction is achieved.This phenomenon is obvious in the entire turbulent boundary layer.