Modelling of sediment suspensions in oscillating grid turbulence
Résumé
A $k–ε$ model is used to describe the steady state of fine-grained sediments maintained in suspension by purely diffusive turbulence, as generated in oscillating grid turbulence experiments. The behaviour is shown to depend both on the bulk Rouse number $Rou_0$ and the product of the bulk Rouse number and the bulk Richardson number $Ri_0 Rou_0$, built on oscillating grid parameters. For $Rou_0 < 0.01$, concentrated suspensions are observed with a homogeneous particle concentration in the suspension layer. An interface, called lutocline, separates the suspension layer from the clear water at a distance $z_m$ from the grid. The depth of the suspension layer is found to vary as $z_m/z_0∝(Ri_0 Rou_0)^{−1/4}$. For $Ri_0 Rou_0 \ll 1$ the decay of turbulence is affected by the particle concentration only in a region very close to the interface. In this case the flux Richardson number approaches the value of 1 near the interface. The lutocline is seen to vanish for large values of $Rou_0$. For $Rou_0 > 0.01$, the mean sediment concentration and turbulence decay simultaneously with increasing distance from the grid, and no sharp interface is observed.
Origine : Fichiers produits par l'(les) auteur(s)
