Etude expérimentale et numérique du transport de sédiment dans un coude à 90°

Details

Supervisors

Soares Frazao, Sandra

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil des constructions

Abstract

enPredicting the morphological changes induced by fast transient flows such as flash floods or dam-break flows is still a challenging task, especially when sediment transport is considered. In order to validate numerical simulation tools designed for such flow conditions, reliable experimental data is needed. In previous experiments performed over a fixed bed, it was observed that the fast one-dimensional dam-break wave issued from the reservoir first reflects against the bend, then a hydraulic jump is formed and starts moving back in the upstream direction and, at the same time, the remaining part of the initial wave propagates further downstream with strong two-dimensional flow patterns due to the sudden change in flow direction. In this paper, experiments of the same type are presented, but over a mobile bed made of coarse uniform sediments. The initial conditions consist of a constant water-depth in the upstream reservoir and a saturated sediment bed with an initial thickness downstream. Due to the strong reflection of the flow in the bend, complex morphological patterns can be observed, with significant erosion and deposition. Measurements were obtained using non-intrusive devices to capture the free-surface evolution as well as the bed morphological evolution. The free-surface evolution was measured using ultrasonic probes at several locations. The bed morphological evolution was measured using digital imaging devices and a laser-sheet to isolate given cross-sections of the flow on the images. Such a technique proved its efficiency in slower flow conditions, but its application to the present case with a fast flow involving significant sediment transport is challenging. These measurements were then compared to numerical simulations performed using a finite-volume scheme with a lateralized Hart-Lax-Van Leer-Contact scheme for the flux predictions. This scheme solves in a coupled way the system composed by the shallow-water equations and the Exner equation for the bed morphology. Sediment transport is predicted using the Meyer-Peter and Müller formula. Finally, a discussion of the numerical results is proposed, through the comparisons with the experimental data.