Preliminary experimental investigation on the interaction of a subaqueous dune like granular structure with a turbulent open channel flow

Abstract

We study the interaction of a subaqueous dune like granular structure with a turbulent open channel flow experimentally using optical diagnostics in the Shields and Froude parameter space ($0.05{\leq}{\theta}{\leq}0.32$, $0.1{\leq}Fr{\leq}0.4$). Interactions between the turbulent flow and the granular structure give rise to transient erosion-deposition dynamics leading to various types of particle transport. The subaqueous structures in the channel bed evolves due to shear-stress-induced erosion, gravity-driven deposition, and subsequent particle transport. We study the centroid motion and the granular structure shape evolution. At lower end of our ${\theta}-Fr$ parameter space, we observe no erosion and the structure remains at rest. We show that the critical Shields number (${\theta}_{cr}$) is of the order of $0.1$ beyond which erosion starts to occur. At intermediate values of ${\theta}$ and $Fr$ we observe slow erosion, resulting in a rigid body motion of the granular structure without significant shape deformation. Higher values of ${\theta}$ and $Fr$ causes vortex formation at the upstream of the dune resulting in stronger erosion, rapid shape deformation and relatively higher translation velocity of the centroid.