Flow dynamics and bed morphology in a narrow channels: A comparative study of experimental and numerical approaches to velocity distribution

Abstract

The effects of narrow channels on flow structure and hydrodynamics have been widely studied. However, due to the complexity of flow dynamics in narrow channels, three-dimensional flow properties have rarely been explored. This paper presents a novel experiment investigating the influence of narrow channels with an aspect ratio of 4.615 on three-dimensional turbulent properties and bed morphology. The findings contribute to a deeper understanding of how narrow channels impact turbulent properties and bed feature dynamics in mobile bed flows. The results showed that longitudinal velocity is higher towards the centre and free surface, while vertical velocity shows upward flow near the bed and downward flow towards the free water surface, with intensities varying across the channel. Experimental longitudinal velocity was compared numerically using the Realizable k-ε model by Ansys Fluent software and an analytical model. Both models performed well in predicting values, with the analytical model showing slightly higher accuracy as indicated by statistical indices. Turbulent kinetic energy and Reynolds shear stress are higher close to the bed and banks of the channel. Bed features generates ripple bedforms, which are dynamic and complex, influenced by flow dynamics, sediment transport, and channel geometry, creating a rich and intricate flow environment. The three dimensional skewness and kurtosis are also explored in this paper. This information is valuable for river or canal design engineers, with implications for stability and navigation, and it can guide maintenance strategies for narrow rivers and canals.