Cavitation bubbles: a tracer for turbulent mixing in large rivers

Abstract : On the Seine river in Paris, the high frequency of tourist boats traffic may exert a significant impact on transport of sediments and thus on transport and residence time of pollutants. To have a better understanding of anthropogenic effects and more generally to study rivers suspended sediments dynamics, it is essential to quantify the river transport capacity. Turbulent mixing is one of these transport mechanisms and we present here a simple technique to estimate lateral coefficient using ADCP backscatter signal analysis. We realized several static measurements during low water discharge (Q = 140 cubic meters per second) in which we can see a strong correlation between high backscatter values and the passage of boats. We argue that these high backscatter values, in the center of Paris city, are not due to a sediment plume but to cavitation bubbles. These high values suggest that resonant, ~10 micron bubbles are present in the flow in agreement with LISST grain size measurements. Given their slow ascent velocity these particles can be used as passive markers to estimate the lateral turbulent mixing coefficient. For this purpose we develop a dimensionless form of the sonar equation that, when coupled to a simple lateral turbulent diffusion model, allows to compute lateral diffusion coefficients. These estimates of lateral diffusion coefficient have an important implication for representative river water sampling and can be very useful to calibrate numerical models of river flow and sediment transport.
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Communication dans un congrès
River, Coastal and Estuarine Morphodynamics, 2011, Beijing, China. River, Coastal and Estuarine Morphodynamics: RCEM2011, 2011
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  • HAL Id : hal-01501296, version 1

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H Chauvet, F Métivier, A Limare. Cavitation bubbles: a tracer for turbulent mixing in large rivers. River, Coastal and Estuarine Morphodynamics, 2011, Beijing, China. River, Coastal and Estuarine Morphodynamics: RCEM2011, 2011. 〈hal-01501296〉

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