Abstract
In order to analyze the shear effect of secondary currents on the flow structures in a meandering channel, this research developed a two-dimensional shallow water model, which included the dispersion stress term accounting for the shear effect in the vertical velocity profile. A new equation for the vertical velocity profile that included nonlinear shear effects was derived from the equation of motion in the meandering channel with sharp curvature. Using the experiment data obtained from large-scale meandering channels, the ratio of the depth over the radius-of-curvature was incorporated into the shear intensity of the secondary flow in the proposed equation. Comparisons with the experimental results by previous research showed that the computed values of the primary velocity distribution by the proposed model showed better fit with the observed data than the simulations with linear models and models without secondary flow consideration. The simulated results in the large-scale meandering channels demonstrated that simulations with the nonlinear secondary flow effect added into modeling gave higher accuracy, reducing the relative error by 19% in reproducing the skewed distributions of the primary flow in meandering channels, particularly in the regions where the effects from spiral motion were strong, due to sharp meanders.
Highlights
Modeling of the primary and secondary flows in a meandering channel is a challenge compared to straight channels, due to the complication in flow structures
Large-scale experiments were conducted in the KICT River Experiment Center (REC) meandering channels to find the nonlinear effect of the secondary current on the primary flow distribution
The proposed velocity profile equation was inserted into the momentum equations with the dispersion stress method in order to induce the nonlinear shear effect of the secondary flow, which is normally neglected in the depth averaging process
Summary
Modeling of the primary and secondary flows in a meandering channel is a challenge compared to straight channels, due to the complication in flow structures. This secondary flow in meandering channels is caused by the local imbalance between the transverse water pressure forces generated by the super elevation of the water surface, and the vertically varying centrifugal force [1]. The advective momentum transport by the secondary flow causes longitudinal velocity redistribution, in which the primary flow is shifted to the outer bank, as shown in Figure 1 [2]. Understanding of the shear effect of the secondary flow in bends is necessary in order to analyze the transverse distribution of the longitudinal velocity, as well as to study the mixing of sediments and pollutants in meandering channels
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