Cyclone: Fly Ash

Fly Ash Cyclone CFD Simulation, ANSYS Fluent Training

Description

This project simulates the motion of particles within a fly ash cyclone using ANSYS Fluent, employing a one-way DPM approach to model the discrete phase. A cyclone is a device used to separate particles from a gas stream, with widespread applications across industrial processes.

A cyclone separator is a particulate control system used to limit particulate emissions into the atmosphere — efficient, cost-effective, and low in energy consumption. It separates particles of varying sizes from a gas stream using centrifugal force, and although the design is somewhat complex, its high separation efficiency more than compensates. Structurally, cyclones consist of an upper cylindrical barrel, where separation occurs, and a lower conical section, where separated particles are collected.

The cyclone's flow field and separation performance are shaped by gas-solid interactions within it. Since particle loading remains relatively small, the presence of particles doesn't meaningfully alter the flow field, though the coupled particle effect on the surrounding stream remains significant. The separation principle relies on inertia: particles with higher density carry greater inertia, causing them to revolve at a larger radius. Heavier particles spiral outward toward the wall and slide downward, while lighter particles rotate closer to the center and are drawn out through the top.

This simulation uses the Eulerian-Lagrangian technique: gas is treated as a continuum under the Eulerian framework, while individual solid particles are tracked through the flow field using Lagrangian tracking. Given the large density ratio between gas and particles, both drag and gravitational forces play a significant role in this simulation.

Geometry & Mesh

The 3D geometry was built in SpaceClaim and meshed in ANSYS Meshing using an unstructured grid totaling 1,028,959 cells.

Methodology

Several assumptions were applied to the simulation: a pressure-based solver was used, the simulation was run as unsteady, and gravitational effects were included at -9.81 m/s².

Key simulation settings included:

• Viscous model: Reynolds Stress model

• Discrete phase: Enabled with unsteady particle tracking; anthracite defined as the injected material, treated as inert, using a group injection type

• Boundary conditions: Velocity inlet at 5.9 m/s with discrete phase set to escape; pressure outlet at 0 Pa gauge pressure with discrete phase set to escape; stationary walls with discrete phase set to reflect

• Solution methods: SIMPLE pressure-velocity coupling, second-order discretization for pressure, first-order for momentum, and first-order upwind for the modified turbulent viscosity

• Initialization: Hybrid method

Conclusion

The simulation examined particle motion throughout the cyclone alongside contours of particle velocity, pressure, and gas flow. The results confirm that lighter and heavier particles separate as expected, driven by the combined effects of centrifugal force and gravity. Most particles entering through the inlet exit through the lower outlet, while air exits through the upper outlet — though a small fraction of particles become trapped in the upper section of the cyclone rather than following either primary exit path, consistent with the separation behavior observed in similar cyclone configurations.