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On turbulence-induced settling modification and the consequences on suspension models.


Thibaud Revil-Baudard

In the literature, the influence of the turbulence on solid particles settling velocity has been clearly highlighted. Depending on the turbulence and sediment properties, either a retarded or increased settling is observed compared with the settling velocity value obtained in still-water.

Settling experiments in a turbulence column have been realised in Karlsruhe to study the underlying mechanisms and to investigate the link with suspension sediment transport. Several particles types has been used with a relatively wide range of diameter, shape and density. Particularly, the plastic sediment particles which have been used in the intense sediment transport experiment in the LEGI tilted flume have also been used in the turbulence column.

The results obtained from image analysis (PIV and tracking) show the significant settling retardation induced by the ambiant turbulence. The analysis seems to indicate that this observed retardation is rather linked to non-linear drag effects on the particles. The consequences on the suspension models such as the Rouse model will be discussed in the presentation. A direct link between the turbulence induced settling retardation and the Schmidt number modification is suggested.