Open Channel Flow: Pollution Spread in the Stagnant River

Pollution Spread in a Stagnant River, ANSYS Fluent Training

Description

This project simulates the entry and spread of a pollutant into a stagnant river using ANSYS Fluent.

The core of this case is open-channel flow — flow in a channel or river whose upper surface is open to the atmosphere and free to deform, rather than being fully enclosed by walls. In open-channel problems the position and shape of the free surface is part of the solution, and gravity governs how the water and anything riding on it settle and move. A river receiving a discharge is a natural example: the pollutant enters at the surface and spreads across it, so tracking that free surface is essential, which is exactly what the open-channel (free-surface VOF) approach is built for.

The application itself is an environmental one. Water pollution from industrial waste is a serious concern: chemical by-products discharged into rivers endanger aquatic life and can enter the human food chain through it, causing disease. Simulating how a pollutant disperses once it reaches a river helps predict how far and how fast contamination travels.

The 3-D geometry was built in Design Modeler, with a river inlet width of 11.05 m. The domain was meshed in ANSYS Meshing with 161,562 elements, and because the spreading process evolves in time, a transient solver is used.

Simulation Methodology

The two phases — water and pollutant — are handled with the VOF multiphase model. The pollutant enters through a non-uniform profile partway along the river and diffuses into the water. Because its density is lower than that of water, it floats and spreads along the free surface. Turbulence is solved with the realizable k-ε model using scalable wall functions, pressure-velocity coupling is SIMPLE, and momentum and the volume fraction use second-order upwind discretization. The river water itself is initially stagnant, and the pollutant enters at 8 m/s.

Results & Conclusion

After solving, contours of velocity, pressure, and pollutant volume fraction were obtained. The results show the pollutant progressively diffusing into the river water over time, with the pressure near the pollutant inlet higher than elsewhere. The cross-sectional pressure contour also shows pressure increasing with depth, as expected for a body of water under gravity.