Numerical simulation of 3D flow at 90o straight-channel confluence with bed elevation discordance

Abstract

The paper aims at studying the effect of difference in bed elevations between the tributary and main canals (∆zT) on the flow in the confluence hydrodynamics zone. To do this, a 3D numerical model is used for flow simulation at 90 confluences with four different values of the ∆zT/h ratio (where h is the water depth in the main canal at the confluence). The values are in the range [0.0, 0.5]. The ∆zT /h = 0.00 case corresponds to the concordant beds confluence, and the value of 0.50 is the common value in field confluences. Special attention is paid to the flow deflection and recirculation zones. It is found that: 1) the vertical velocity component attains the same order of magnitude as the horizontal velocity with the increasing ∆zT , 2) the enhanced 3D flow close to the side-wall shifts the recirculation zone away from the wall to the boundary streamline, thus changing the recirculation zone orientation whose axis becomes inclined at an angle to the wall, 3) the size of the zone is reduced and 4) the structure of the zone is completely destroyed close to the free surface, where the core of the w_max is located.