Author(s): Mario J. Franca; Rui M. L. Ferreira; Ulrich Lemmin
Keywords: No Keywords
Abstract: In natural low relative submergence flows over gravel beds, different length scales exist simultaneously, ranging from grain configuration-to channel configuration-scales. Consequently, a wide range of time-scales co-exist which may be analyzed in an Eulerian frame. By taking into account the interaction between scales, the formal theoretical framework of these flows renders more complex. The present research contributes towards a multiscale analysis of river flows by studying the crosscorrelation partition between eddy-scales in several flow layers. The present study is based on 15 instantaneous 3D velocity profiles that were measured by means of an ADVP with a vertical resolution of 5 mm in a 0. 30 x 0. 40 m 2 horizontal grid for 3. 5 min each with an acquisition frequency of 26 Hz. Flow structures were isolated and characterized by their time-scales by means of conditional sampling techniques and wavelet multilevel decomposition of single point instantaneous velocity measurements. For this analysis, an eight wavelet decomposition was applied to velocity measurements in a gravel-bed river with low relative submergence (h/D 50 =2. 9). The cross-correlation between the isolated structures and the remaining signal was estimated. The global contribution of a particular scale to total normal stresses and also to local stresses within one coherent structure phase cycle is thus examined and analyzed.