[S-CG46] Rheology, fracture and friction in Earth and planetary sciences

[SCG46-P07] Study of the mobile granular layer in bedload transport by laminar shearing flow in a tilted channel

*Chong-Wei Hong¹, Franco Tapia², Pascale Aussillous³, Élisabeth Guazzelli⁴, Chi-Yao Hung¹ (1.Department of Soil and Water Conservation, National Chung Hsing University, Taichung, Taiwan, 2.Department of Mechanical Engineering, Tokyo University of Agriculture and Technology, Tokyo, Japan, 3.Aix-Marseille Université, CNRS, IUSTI, Marseille, France, 4.Université de Paris, CNRS, Matière et Systèmes Complexes (MSC) UMR 7057, Paris, France)

Keywords:granular media, particle/fluid flow, sediment transport

Erosion is a natural phenomenon which moves materials from the earth's surface thanks to a shearing fluid, and has a significant effect on the morphodynamics of river beds. When sands and rocks are transported, this process is hard to clarify since we can only observe the surface motion. Following previous work to investigate experimentally the mobile layer of a granular bed due to a shearing fluid flow we use a refractive index matching technique. The experimental setup consists of a rectangular channel partially filled with particles as shown in the figure. We use index-matched combinations of spherical hydrogel particles and a mixture of water, citric acid, and ucon oil to control the hydrogel particles diameter (which have swelled in the fluid) and the fluid viscosity. The tube is tilted, between 20 deg and 40 deg, and we impose an upward fluid flow thanks to a pump, which ensures a stationary regime. Indeed, the upper layers of particles are transported upstream due to the fluid shearing flow whereas the granular bed tends to slide down due to gravity. Both particle and fluid velocity profiles are obtained using particle image velocimetry. The experimental results are compared with a two-phase continuum model having frictional rheology to describe particle-particle interactions. By varying the viscosity of the fluid, we study the influence of inertia while staying in a laminar regime. We also focus on the role of the elasticity of the particles on the frictional rheology.