Water Discharge: Rotating Tank

Water Discharge of a Rotating Tank, ANSYS Fluent CFD Simulation Training

Description

This project simulates the water discharge of a rotating tank using ANSYS Fluent, applying the Volume of Fluid (VOF) model to solve the two-phase flow field, with air as the primary phase and water as the secondary phase. The tank rotates about the Y-axis at 80 rev/min, with water discharging through two circular orifices located at the bottom of the tank.

The geometry was generated in Design Modeler, modeling the tank as a cylinder with a diameter of 1 m and a height of 0.75 m, with each orifice measuring 150 mm in diameter. The domain was meshed in ANSYS Meshing using an unstructured grid throughout, totaling 470,369 elements.

Methodology

Several assumptions were applied to the simulation: given the incompressible nature of the flow, a pressure-based solver was selected, the simulation was run as transient, and gravitational effects were included at -9.81 m/s² along the Y-axis. The tank wall was assigned a rotational speed of 80 rpm about the Y-axis.

Key simulation settings included:

• Multiphase model: VOF with two Eulerian phases (air and water), sharp interface modeling, and explicit formulation

• Viscous model: Standard k-epsilon with scalable wall functions

• Material properties: Air (density 1.225 kg/m³, viscosity 1.7894×10⁻⁵ Pa·s); water (density 998.2 kg/m³, viscosity 0.001003 Pa·s)

• Boundary conditions: Pressure outlet at both the main outlet and orifice; tank wall defined as a moving wall rotating at 80 rev/min about the Y-axis (origin at 0,0,0)

• Solution methods: SIMPLE pressure-velocity coupling, PRESTO! for pressure discretization, second-order upwind for momentum, first-order upwind for turbulent kinetic energy and dissipation rate, and a compressive scheme for volume fraction

• Adaption controls: A cylindrical registration region (0.5 m radius, extending along Y from 0 to 0.6 m) used to define the initial water patch

• Initialization: Standard method, with the water phase patched into the defined cylindrical region at a volume fraction of 1

• Run settings: Time step size of 0.02 s, maximum 20 iterations per time step, over 700 total time steps

Conclusion

Results include contours of pressure, water volume fraction, eddy viscosity, and streamlines. The results clearly show that, under the combined influence of gravity and the tank's rotational motion, the water within the cylindrical tank rotates about the Y-axis as it discharges through the orifices — with the volume fraction contours tracing how the water body deforms and thins near the orifice openings as it exits. The streamline patterns further illustrate the swirling discharge behavior induced by the tank's rotation, showing how angular momentum imparted by the moving wall carries through into the exiting flow. Together, these results confirm that the rotating reference imposed on the tank wall successfully couples with the VOF-tracked free surface to reproduce the expected swirl-driven discharge pattern through both orifices.