Circular Weir: Eulerian 3-Phase Flow of Air, Water, and Sand

Description

This project simulates the three-phase flow of water, air, and sand over a circular weir using ANSYS Fluent, investigated through CFD analysis. When an obstacle is placed in the path of a flow, it causes the fluid level to rise behind it and the velocity to increase, eventually leading the fluid to spill over the obstacle; structures of this kind are known as weirs. Weirs take various forms depending on their intended use and are widely employed in civil and agricultural water management — for controlling and measuring flow in irrigation channels, canals, and other water-conveyance systems central to agriculture.

The model was built in 2D using SpaceClaim. Meshing was performed in ANSYS Meshing, producing 4,770 elements.

Methodology

In this simulation, water enters the computational domain at a velocity of 1 m/s and flows over a sand bed situated behind the weir. As it passes over the weir, the flow lifts some of the sand and carries it downstream.

The standard k-epsilon model is used to solve the turbulent flow equations, while the Eulerian multiphase model is employed to capture the motion of and interaction between the three phases — water, air, and sand.

Conclusion

On completion of the solution, two-dimensional contours of the volume fraction of the air, water, and sand phases, along with pressure, streamlines, and velocity vectors, were obtained.

As the sand volume fraction contour shows, the water flow lifts a portion of the sand from the bed and transports it as it spills over the weir. Over the long term, the sand bed behind the weir is washed away entirely, and the emptied region behind the circular obstacle becomes a tangential path for the water — illustrating the sediment-transport and scouring behavior that is important when designing weirs for irrigation and agricultural water systems.