Study of Junction Angle Effect on Flow Characteristics at Channels Confluences

Open channel confluences are present in many man-made and natural waterways; such as irrigation and sewage networks and river systems. In this research, it has been attempted to simulate the junction flow in rectangular channels by utilizing, Volume of Fluid (VOF) scheme and RSM based turbulence models of FLUENT software. The effect of branch channel angle on flow behavior pattern and free surface water level for angles 30^০,45^০, 60^০ and 90^০ are studied The results show that reduction of branching angle leads to a decrease in water level at the upstream of the cross point and to an increase in water level at the downstream of it. Upstream depths of water at the cross point are found 2%, 4.3%, 6% and 9% higher than the junction depths of  water at the downstream for the angles of 30^০,45^০, 60^০ and 90^০, respectively. A separation zone and a stagnation point are formed in the main channel at the downstream and upstream corner of the junction, respectively. The decrease of cross angle causes the reduction of separation zone dimensions and flow turbulence. Simulation of the shear stress distribution illustrates high shear stress concenteration on the opposite wall of the junction point and it increases with increase of the junction angle. With increase of channel junction angle, the separation zone dimensions increase and the effective width of the channel for the transition of the flow to downstream reduces. Reducing the junction angle and consequently reduction of the separation zone dimiensions helps to reduce the crossing problems of the two flows confluence.