Érosion et transport de particules au voisinage d'un obstacle

Abstract : Erosion occurs when a fluid flowing over a granular bed exerts a large enough shear stress. When the fluid encounters an obstacle, the modification of the flow leads to a local over speed, and thus on an increase of the shear stress in the vicinity of the obstacle. As a result, the erosion is locally enhanced and is called scouring. In this work, we investigate this complicated situation experimentally at the laboratory scale. In particular, we address the question of the scouring threshold, i.e., the minimum critical approach velocity of the fluid leading to erosion in the vicinity of the obstacle. We report the existence of two different scouring patterns: the traditional horseshoe scour at the base of the obstacle, which dominates at large flow velocities, and we also highlight another scouring pattern downstream, which is called rabbit ear scour, at moderate speeds. We determine the onset of both erosion patterns visually using different grains and obstacles. Besides, we measure the bed topography over time using a laser profilometer. By monitoring the bed topography during the scouring process, we characterize the morphology of both scouring patterns and rationalize their competitive dynamics by measuring their formation timescale. In most cases, the rabbit ear scour development is inhibited by the faster horseshoe scour growth. The characterization of the flow using Particles Image Velocimetry (PIV), provides information on the shear stress exerted by the fluid flow on the grains, with and without obstacle. We can thus rationalize the threshold values for both scouring patterns, associated with different flow structures.
Complete list of metadatas

Cited literature [18 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-02276246
Contributor : Abes Star <>
Submitted on : Monday, September 2, 2019 - 2:09:06 PM
Last modification on : Wednesday, September 4, 2019 - 1:15:16 AM

File

73660_LACHAUSSEE_2018_archivag...
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02276246, version 1

Collections

Citation

Florent Lachaussée. Érosion et transport de particules au voisinage d'un obstacle. Mécanique des fluides [physics.class-ph]. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLS377⟩. ⟨tel-02276246⟩

Share

Metrics

Record views

80

Files downloads

34