Wavelet analysis to detect multi-scale coherent eddy structures and intermittency in turbulent boundary layer

The velocity time sequence at different vertical locations in a turbulent boundary layer has been finely measured by IFA300 constant-temperature anemometer with resolution higher than the frequency that corresponds to Kolmogorov dissipative scale. The velocity signals are decomposed into multi-scale eddy structures by wavelet transform, which describes the local averaged structure function and relative strain distortion for multi-scale eddy structures in turbulent flows. The temporal scales of multi-scale coherent eddy structures are determined by auto-correlation function. A conditional sampling technique for multi-scale coherent eddy structures detection from simultaneous turbulent field has been introduced using multi-scale instantaneous intensity factor and multi-scale flatness factor of wavelet coefficients. Coherent eddy structures for different scales are extracted by this technique and the dynamics course of multi-scale coherent eddy structures is studied by their phase averaged velocity evolution shapes. Extended self-similarity scaling law is calculated using wavelet coefficients, and the influence of coherent eddy structures on extended self-similarity scaling law is also analyzed. The multi-scale coherent eddy structure evolution shapes extracted from turbulent field at small scales are similar and they are responsible for the anomalous scaling law in boundary layer. When such multi-scale coherent eddy structures are eliminated, intermittency anomalies are no longer observed and the Kolmogorov linear scaling prediction is resumed.