Journal article

Turbulent particle flux and momentum flux statistics in suspension flow

The particle entrainment ability of coherent flow structures is investigated by comparing statistical properties of momentum flux u'w' and of turbulent mass fluxes c'u' and c'w' in suspension, open-channel flow under capacity charge conditions. The quadrant repartitions of these quantities as a function of the corresponding threshold levels are estimated. A cumulant discard probability density distribution is used to calculate the theoretical quadrant dynamics. Good agreement between the third-order model and the experimental results is found for all investigated quantities in the wall and intermediate flow regions. In the free surface domain, the increase of intermittency of the momentum and mass transport processes leads to small discrepancies between the model and the experimental results. The quadrant distributions of the horizontal and vertical turbulent mass fluxes are dominated by the same two quadrants as the momentum flux u'w'. Ascendent mass flux events are found to correlate with ejections over the entire water depth. A dynamical equilibrium between the shear stress production term and the turbulent energy dissipation term is found in the intermediate flow region where the value of the normalized vertical flux of turbulent kinetic energy in suspension flow corresponds well with the one observed in clear water flows. This points toward a universality of the normalized vertical flux of turbulent kinetic in highly turbulent boundary layers. The suspended particle transport capacity of coherent structures is directly quantified from the estimation of the conditionally sampled terms of the particle diffusion equation. Coherent structures are found to play a dominant role in the mass transport mechanism under highly turbulent flow conditions in open-channel flows.


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