Detecting Multi-Scale Coherent Eddy Structures andIntermittency in Turbulent Boundary Layer by Wavelet Analysis

Abstract

Multi-scale decomposition by wavelet transform has been performedto velocity time sequences obtained by fine measurements of turbulentboundary layer flow. A conditional sampling technique for detectingmulti-scale coherent eddy structures in turbulent field is proposed byusing multi-scale instantaneous intensity factor and flatness factor ofwavelet coefficients. Although the number of coherent eddy structuresin the turbulent boundary layer is very small, their energy percentagewith respect to the turbulence kinetic energy is high. Especially inbuffer layer, the energy percentages of coherent structures aresignificantly higher than those in the logarithmic layer, indicatingthat the buffer layer is the most active region in the turbulentboundary layer. These multi-scale coherent eddy structures share somecommon dynamical characteristics and are responsible for the anomalousscaling law in the turbulent boundary layer.