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Analysis of the Autocorrelation Within Turbulent Scales in a Gravel-Bed River

Author(s): M. J. Franca; R. M. L. Ferreira; U. Lemmin

Linked Author(s): Ulrich Lemmin, Mário Franca, Rui M.L. Ferreira

Keywords: No Keywords

Abstract: In river flows, mesoscale organized motion contributes more to strong local variations in transport, mixing and gastransfer processes than small-scale background turbulence. By applying wavelet decomposition to ADVP field measurements in a gravel-bed river with low relative roughness (h/D84=2. 94), we studied the autocorrelation distribution of different modes throughout the eddy scales. We present an analysis of the autocorrelation scale partition in several layers of the water column. An eight level wavelet decomposition of the turbulent velocity signal, using the Daubechies‘D4’wavelet type, provided sufficient resolution to describe the modes’energy partition over the turbulence scales. The highest correlated scales are found to be of the same order of magnitude or smaller than the water depth h. The curve corresponding to the autocorrelation distribution over the scales is characterized by the peak value and a dimensionless parameter representing the modes’energy dispersion through eddy scales. Both the structure scale corresponding to the peak value of the autocorrelation and the dispersion parameter are estimated and discussed.


Year: 2010

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