Author(s): Luiz Eduardo Domingos De Oliveira; Johannes Gerson Janzen; Carlo Gualtieri

Linked Author(s): Luiz E. D. de Oliveira, Carlo Gualtieri

Keywords: Lateral cavity; Geometric shape; Sediment transport; Large eddy simulation (LES); Computational fluid dynamics (CFD)

Abstract: Lateral cavities are hydraulic structures that function as transient storage zones in natural streams. This structure plays a key role in mass related processes due to its transient storage capabilities. In rivers, this structure is used to retain sediment and mitigate accidental spillages, but also on the nutrient retention and release promoting vegetation growth. The flow and mass transport in lateral cavities depend on an aspect ratio between width (W) and length (L) that determines the quantity and the shape of the recirculation flow inside the cavity. Although, the influence of different geometric shapes remains uncertain and needs further study. This numerical study aims to assess the impact of geometric shapes on the hydrodynamics and mass exchange of a lateral cavity. The cavity was L = 0.25 m long (x-axis), W = 0.15 m wide (y-axis) and had a depth of H = 0.10 m (z-axis). The aspect ratio was W/L = 0.6 which corresponds to a single circulation system. The bulk velocity in the undisturbed channel was U = 0.101 m/s with a Reynolds number of 9000. The flow field was calculated with Large Eddy Simulation (LES) and the subgrid effects were accounted with the Wall Adapting Local Eddy-viscosity (WALE). The numerical model was validated using literature experimental data and the errors were calculated using three different meshes. The mean error in the velocity fields was 1.74% inside the cavity. Preliminary results showed that inside the cavity a single circulation occurred with a uniform distribution of velocities. Despite the uniform distribution of velocities, the estimative of the sedimentation fields showed that accumulation is prone to occur in the middle-upstream section of the cavity, as this region is far from the initial jet that occurs in the most downstream part. Additionally, sediment transport mode was not influenced by the flow, as the particle settling velocity was dominant over the other effects inside the cavity.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221064

Year: 2022