Numerical study of 3D flow at right-angled confluences with and without upstream planform curvature

Abstract

The purpose of this paper is to study the individual and combined effect of upstream planform curvature and difference in bed elevations at the tributary entrance to the confluence on the flow in the confluence hydrodynamics zone. To do this, flow at right-angled confluences with three planforms and four values of bed elevation discordance ratio (Delta Z(T)/h(d)) is simulated using a three-dimensional (3D) numerical model. Three confluence planforms include confluences with the (1) straight tributary canal (Sc), (2) right bend (RB) and (3) left bend (LB) in the tributary. Four Delta Z(T)/h(d) values in the range [0.0, 0.5] include both concordant and discordant beds' confluences. Overall, nine cases with the straight main canal are considered. Special attention is paid to the flow deflection and flow separation zones since the former affects transfer of momentum from the tributary to the main canal and the latter affects transport capacity of the post-confluence channel. Comparison of the results reveals that the influence of RB in the tributary is practically negligible in comparison to the straight canal case. With the increasing difference in bed elevations between the tributary and main canals (Delta Z(T)), the presence of LB strengthens 3D flow and the structure of the recirculation zone is destroyed.