Combining CFD and DEM using Ansys Fluent and ANSYS Rocky may generate a multiphysics simulation of non-spherical particle-fluid interactions. If particles have distinctive forms, these software tools can accurately simulate them. The airflow field solution comes from Ansys Fluent, whereas Rocky DEM computes particle-fluid interaction. This gains importance in the CFD-DEM simulation of particles inside cyclone separators. However, the study relies on the Reference paper entitled “ Numerical study on gas-solid flow characteristics of ultra-light particles in a cyclone separator [1] “.

• Reference [1]: Zhou, Haili, et al. “Numerical study on gas-solid flow characteristics of ultra-light particles in a cyclone separator.” Powder technology344 (2019): 784-796.
• Reference [2]: Hoekstra, A. J., J. J. Derksen, and H. E. A. Van Den Akker. “An experimental and numerical study of turbulent swirling flow in gas cyclones.” Chemical engineering science13-14 (1999): 2055-2065.
• Reference [3]: Wang, B., et al. “Numerical study of gas–solid flow in a cyclone separator.” Applied Mathematical Modelling11 (2006): 1326-1342.

Figure 1: Schematic of cyclone separator [1]

Simulation Process

Following the same methodology and design is one of the underlying steps through the simulation based on a paper. This is why a cyclone separator was created with 8 parts, allowing for later generation of a structured grid. Initially, the gas flow is solved by means of CFD methods using ANSYS Fluent. Then, the gas continuous phase results are transferred into ANSYS Rocky to solve discrete phase particles inside the cyclone separator. The 7-equation Reynolds Stress turbulence model leads us to the most reliable solution for the flow.

Post-processing

The CFD-DEM simulation shows how the particles inside the cyclone dance in a beautiful spiral pattern. When we look at the velocity streamlines, we can see an attractive circular pattern. Near the walls, the speeds reach up to 47 m/s but they drop to about 23 m/s in the middle. This circle is not only pretty, it’s also the main thing that causes separation. ANSYS Fluent took care of the complicated airflow patterns, and ANSYS Rocky followed each particle’s path to see how it reacts to these moving currents. Rocky is an expert at modeling non-spherical particles, which is different from basic simulations and a big deal for real-world industrial uses where particle shapes that aren’t round have a big effect on how they separate.

Figure 2: Streamlines in Cyclone Separator CFD-DEM simulation

The picture of the particle distribution shows how the cyclone separation sorts particles by how much they weigh. Heavy particles (about 3.29e-7 kg) are thrown out by rotational forces and slide down the walls to the bottom, where they gather. Lighter particles, which are blue and weigh between 1.5 and 7 kg, become trapped in the inner vortex core and leave through the top outlet. The cyclone’s shape and flow patterns naturally cause this clear sorting based on mass. The Reynolds Stress model correctly showed the turbulence, including recirculation zones and secondary flows that other models would have missed. This Multiphysics simulation is unique because it combines fluid dynamics and particle mechanics into a single solution. This wasn’t possible before the Fluent-Rocky coupling was made available for commercial use.

Figure 3: Particles colored by mass extracted from ANSYS Rocky