Applicability and limitations of 3D numerical models in predicting the morphological changes at open channel junction

Despite the numerous applications of three-dimensional (3D) numerical models in predicting the morphological changes of the erodible bed in the various hydraulics problems, knowledge regarding its suitability and limitations in predicting the channel junction bed morphological changes is still limited. To fill this research gap, the present study investigates the applicability of a 3D numerical model in predicting bed deformations at a right-angled open channel junction using the computational fluid dynamics software, Flow-3D. The capability of the current numerical model in predicting the bed morphological changes at the junction is tested against the laboratory data available in the literature. The current model satisfactorily simulates the deepest scour zone in the flow contraction area with a percentage error of 4.65, which can be assumed to be quite reasonable. The results show that the deposition bar is poorly simulated. The mismatch in reproducing the junction bed topographies can be mainly attributed to the intrinsic uncertainty associated with various empiricism introduced in the scour model and employed Reynolds-averaged Navier-Stokes model. The present study also demonstrates that Meyer-Peter and Muller equation of bed load transport rate is more suitable for predicting the junction bed morphology compared to the Van Rijn equation and Nielsen equation.