Abstract
River bends are one of the common elements in most natural rivers, and secondary flow is one of the most important flow features in the bends. The secondary flow is perpendicular to the main flow and has a helical path moving towards the outer bank at the upper part of the river cross-section, and towards the inner bank at the lower part of the river cross-section. The secondary flow causes a redistribution in the main flow. Accordingly, this redistribution and sediment transport by the secondary flow may lead to the formation of a typical pattern of river bend profile. It is important to study and understand the flow pattern in order to predict the profile and the position of the bend in the river. However, there are a lack of comprehensive reviews on the advances in numerical modeling of bend secondary flow in the literature. Therefore, this study comprehensively reviews the fundamentals of secondary flow, the governing equations and boundary conditions for numerical simulations, and previous numerical studies on river bend flows. Most importantly, it reviews various numerical simulation strategies and performance of various turbulence models in simulating the flow in river bends and concludes that the main problem is finding the appropriate model for each case of turbulent flow. The present review summarizes the recent advances in numerical modeling of secondary flow and points out the key challenges, which can provide useful information for future studies.
Highlights
Rivers rarely run on straight paths, and most of them run on a curved route
The results showed a good agreement between Reynolds-Averaged Navier–Stokes equations (RANS) and large eddy simulation (LES) in the comparison of the computed bed and side-wall shear stresses
The results show that the mean absolute difference (M.A.D.) of the predicted from the observed bed levels was significant at 0.05 level of risk (α < 0.05) for the k-ω model (6.6 mm) and the k-ε model
Summary
Rivers rarely run on straight paths, and most of them run on a curved route. The flow patterns on river bends are very complicated and have special characteristics. Flow patterns in river bends are affected by certain factors such as the centrifugal force caused by the flow curvature and the vertically varying velocity, the cross-sectional stress, in addition to the pressure gradient in the radial direction due to the lateral slope of the water’s surface. All these factors create a flow called secondary flow (Ghobadian and Mohammadi, 2011) [1], which may significantly affect the primary flow motion and, in turn, affect pollutant dispersion and sediment transport. The secondary flow, according to Rozovskii (1961) [2] and
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