The dynamics and evolution of coherent flow structures over Dunes, Parana River, Argentina.

摘要

This study investigates links between large-scale turbulence, sediment suspension and dune morphology in the Parana River, Argentina. Three-dimensional flow and sediment transport data are decomposed in both time and scale with wavelet analysis, which is used to follow the spatial and temporal evolution of coherent flow structures. Wavelet analysis identifies coherent flow structures at a range of frequencies from 1 to 1x10-3 Hz, although two frequencies are dominant: higher frequency structures with periods of between ∼50 and 100 seconds (0.02-0.01 Hz) and larger structures with periods > ∼200 seconds (0.005 Hz). Cross-wavelet analysis illustrates the high coherence between the upward flux of turbulent fluid and higher suspended loads. Similarly, regions of enhanced suspended load correlate well with streamwise flow deceleration. These events are interpreted as fluid ejections. Several interpretations for coherent flow structure evolution are proposed, including a merging and clustering hypothesis, as well as vortex shedding and wake flapping.