A rotary drum is a large, spinning cylinder used in many industries to mix, dry, or coat solid materials like powders and grains. Understanding exactly how these particles move and mix inside is very important for making better products in fields like medicine, food processing, and mining. To see this complex motion, we use a powerful computer simulation method called Rotary Drum DEM. This technique combines two different types of software.  The Discrete Element Method (DEM), using Rotary Drum Rocky DEM software, tracks every single particle as it tumbles, collides, and interacts with other particles and the drum walls. This Rocky solver gives us a complete picture of the process. By performing a Granular Flow DEM analysis, engineers can study particle segregation, find the best rotation speed, and design better lifters to improve mixing. This simulation is essential for optimizing the performance of these industrial mixers, and our study is based on the methods described in a trusted reference paper [1].

• Reference [1]: Hlosta, Jakub, et al. “DEM investigation of the influence of particulate properties and operating conditions on the mixing process in rotary drums: Part 1—Determination of the DEM parameters and calibration process.” Processes2 (2020): 222.
• Reference [2]: Mesnier, Aline, et al. “Mixing of Bi-Dispersed Milli-Beads in a Rotary Drum. Mechanical Segregation Analyzed by Lab-Scale Experiments and DEM Simulation.” Processes9 (2020): 1166.

Figure 1: The calibration process for virtual material properties, based on the reference study for our Rotating Drums DEM Rocky simulation [2]

Simulation Process: Fluent-Rocky Coupling, Defining Particles and Drum Rotation

For this Rotary Drum DEM Rocky study, we first designed a 3D model of a standard industrial rotating drum. The simulation was set up as Rocky DEM to capture the behavior of both the air and the solid particles at the same time. We injected a mix of three different particle types to study how they would separate. These included small spherical particles (2.5mm), large spherical particles (5mm), and polyhedral particles (3mm). The drum was set to spin at a speed of 15 revolutions per minute (rpm), which is a common speed for industrial mixing. In the Rocky DEM software, we defined all the important properties for the particles, such as their density and friction. The DEM part of the simulation handles all the physics of the particles hitting each other and the drum walls.

Figure 2: Initial setup of the three particle types within the drum for the CFD-DEM Coupling Simulation.

Post-processing: DEM Analysis, Visualizing Particle Velocity and Segregation

The velocity distribution contour gives us a clear view of the motion inside the drum. This professional visual shows that the particles move at different speeds, ranging from very slow (0.008 m/s, blue) to quite fast (1.07 m/s, red). The fastest particles are seen near the drum wall, where they are lifted up by the rotation, reaching speeds close to 1 m/s. These particles then fall back down into the main pile of material. At the very bottom of the drum, we see a large area of blue, indicating a slow-moving bed of particles where most of the gentle mixing happens. The lifters attached to the drum wall create localized areas of higher velocity (green and yellow) as they scoop up material and drop it, which helps to stir everything more actively.

Figure 3: Translational velocity distribution from the Rotary Drum Rocky DEM analysis, showing speeds from 0.008 m/s to 1.07 m/s at a rotation of 15 rpm.

The cross-section view of the particle sizes reveals a very important behavior called segregation. The color coding clearly shows that the different particle types have separated. The large, 5mm spherical particles (red) have gathered near the center and bottom of the mixing pile. In contrast, the smaller, 2.5mm particles (blue) are spread more evenly throughout the drum. This happens because the larger particles have more energy and tend to roll down the pile to the bottom. The 3mm polyhedral particles (light blue and green) are found in between. While the lifters help to fight this segregation, they cannot stop it completely. The most important achievement of this simulation is the successful use of a DEM model to accurately predict  the complex particle segregation patterns inside a rotary drum. This provides engineers with a powerful and trustworthy digital tool to optimize lifter designs and operating conditions to achieve better, more uniform mixing in real-world industrial applications.

Figure 4: Particle size distribution from the Particle Segregation analysis, showing how larger (red) and smaller (blue) particles separate during rotation.