Hydrodynamic characteristics in pools with leafless vegetation under ice-covered flow conditions − an experimental study and numerical simulation

Abstract

This study investigates the impact of submerged rigid leafless vegetation on the hydrodynamic characteristics in pools and explores the turbulent kinetic energy profile of flow under ice-covered flow conditions. To investigate the effects of leafless vegetation on flow velocity, turbulent kinetic energy, and secondary flow variations, laboratory experiments have been conducted in a large-scale outdoor flume considering different water surface cover conditions, submergence heights of vegetation, pool features, and hydraulic conditions. The Re-Normalization Group (RNG) k-ε turbulence model, implemented in Flow-3D (CFD) software, has been used to simulate fluid dynamics in the channel with pools. The results indicate that vegetation transforms the vertical distribution of main flow velocity within the vegetated zone from a logarithmic shape to a quasi-S shape. Compared to the non-vegetated conditions, vegetation in the pool bed induces notable disturbances in lateral velocity, fostering the formation of secondary currents across the pool cross-sections. The velocity decreases within the vegetated zone in the pool. Still, it increases as the height of vegetation rises, suggesting that vegetation significantly obstructs flow in the pool and creates a slow flow zone, potentially enhancing habitat suitability for aquatic organisms near the pool bottom. Turbulent kinetic energy exhibits significant changes near the vegetation tops, with the maximum values observed at the vegetation-water interface under open channel flow conditions forming a mirrored “C” shape, indicating substantial energy exchange at this boundary. In the presence of an ice cover on the water surface, the turbulent kinetic energy demonstrates a sharp increase near the surface. As inflow increases, the turbulent kinetic energy along the water depth in the pool increases. This study demonstrates that Flow-3D software effectively simulates the impact of leafless vegetation on the hydrodynamic characteristics of channels with pools, providing valuable insights for flood control, riverbank restoration, and ecological protection efforts.