Open Channel Flow: Water Pollution in the Meandering River

Description

This project simulates pollution transport in a meandering river using ANSYS Fluent, investigated through CFD analysis. Water pollution is the contamination of water bodies — usually the result of human activity — in a way that harms their legitimate uses. Such pollution prevents a body of water from delivering the ecosystem services it would otherwise provide, and it is broadly classified as either surface water pollution or groundwater pollution.

The model was built in 3D using Design Modeler. The river's width at the inlet is 14.035 m, and the pollutant enters through two circular profiles, each 3 m in diameter. Meshing was performed in ANSYS Meshing, producing 762,433 elements. Because of the time-dependent nature of the problem, a transient solver was used.

Methodology

This study employs the VOF (Volume of Fluid) multiphase model to solve the two-phase flow field. To represent the free surface of the river, the open channel option within the multiphase module was enabled, allowing the air–water interface and the gravity-driven surface flow to be captured accurately.

Pollutant enters the river through two circular inlet profiles near its start and then diffuses into the water. Because the pollutant is less dense than water, it accumulates at the river's surface, and the flow carries it downstream, spreading the contamination along the channel.

The Realizable k-epsilon viscous model with scalable wall functions was used to resolve the turbulent flow. Pressure-velocity coupling was handled with the SIMPLE scheme. A second-order upwind scheme was applied to the momentum equations, while a first-order upwind scheme was used for the turbulent kinetic energy and turbulent dissipation rate. Water enters the domain at 35 m/s, and the pollutant enters at 5 m/s.

Conclusion

Once the solution was complete, contours of velocity, pressure, pollutant volume fraction, water volume fraction, eddy viscosity, and streamlines were extracted and presented across different time steps.

As the results show, the pollutant enters the river through the two circular inlet profiles and gradually diffuses across the water surface over time. Driven by the river's flow, the pollution spreads along the free surface and ultimately leads to widespread contamination of the channel.