A Fluidized Bed DEM Rocky simulation is a critical tool for industries like pharmaceuticals and chemical processing. In a fluidized bed, gas is blown upwards through a container of solid particles to make them behave like a liquid. This is great for mixing and drying. However, it is impossible to see inside a real steel tank to know if the mixing is working correctly. A CFD-DEM coupling analysis solves this blindness. It combines two powerful methods: CFD (Computational Fluid Dynamics) to solve the gas flow, and DEM (Discrete Element Method) to track every single particle.

This report details a Fluent & Rocky coupling study. We simulate a binary mixture, which means there are two different sizes of particles. This is very hard to predict because large and small particles like to separate (segregate) instead of mix. By using ANSYS Fluent with Rocky DEM, we can simulate the complex collisions and drag forces that cause this behavior. A DEM CFD simulation is the only way to accurately predict phenomena like bubbling and slugging. This helps engineers design better reactors that mix materials perfectly without wasting energy. For more examples of these advanced particle simulations, please check our DEM tutorials. This study proves how ANSYS Fluent and Rocky DEM work together to solve complex industrial problems.

Figure 1: Showing the Fluidized Bed DEM Rocky model with thousands of particles interacting with the upward gas flow.

Simulation Process: ANSYS Fluent and Rocky DEM Coupling Configuration

The simulation process for this Fluidized Bed DEM Rocky project began by creating a precise 3D domain filled with a high-quality structured grid. The engineers defined a complex binary mixture of particles in Rocky DEM consisting of 4 kg of small particles (6 mm diameter) and 4 kg of large particles (10 mm diameter). To make the collisions realistic, specific material properties were set, including a Poisson’s ratio of 0.3 and a Young’s modulus of 1e+7 Pa. The core of this simulation is the two-way coupling method. This means ANSYS Fluent calculates the gas pressure and velocity and sends this information to Rocky, while Rocky calculates the position of every particle and sends that data back to Fluent to affect the gas flow.

The physics of the gas-solid interaction was carefully defined using the Huilin-Gidaspow drag model. This specific model was chosen because it is very accurate for both dilute flows (where particles are far apart) and dense flows (where particles are packed together). The solver was set to a transient solution, which calculates the flow step-by-step over time to capture the dynamic movement of bubbles and particle circulation. By synchronizing the time steps between the CFD solver and the DEM solver, the Fluent & Rocky coupling accurately reproduced the real-world physics of the fluidized bed.

Post-processing: Engineering Dynamics Inspection

The simulation results provide a “transparent view” into the reactor. We will now inspect the dynamics of the particles to understand if the fluidization is successful or if there are problems with mixing. The rotational velocity contours in Figure 2 act like a “collision detector.” When particles hit each other or the wall, they start to spin.

• The Bubble Effect: At time T1 and T4, we see red and green zones where the rotation is high (up to 433.3 rad/s). These high-energy zones are caused by gas bubbles rising through the bed. As a bubble bursts, it throws particles upwards, causing them to collide violently.
• The Resting State: In contrast, at times T2 and T3, the bed collapses and settles. The colors turn mostly blue (low rotation, 0-217 rad/s). This indicates a “dead zone” where the particles are packed together and not moving much.
• Engineering Insight: This cyclic pattern of “bursting and settling” is the heartbeat of the reactor. The simulation proves that the bubbles are the primary mixers. Without these bubbles, the particles would just sit still and not react.

Figure 2: The absolute rotational velocity and drag force contours. These contours visualize the particle collision intensity and spin at four different time steps (T1, T2, T3, T4) during the CFD-DEM coupling process.

The mass contours in Figure 3 reveal a critical challenge for manufacturers: segregation. We colored the small particles blue (lighter) and the large particles orange (heavier).

• The Separation Problem: At time T2 and T3, we clearly see the orange particles sinking to the bottom (below Y = 0.3 m) while the blue particles float to the top. This is called segregation. The large particles are heavier and fall faster than the gas can push them up.
• The Re-mixing Event: However, at T4, a new bubble rises. We can see the orange particles being pushed back up slightly.
• Engineering Insight: This result is vital for designers. It shows that the current gas speed is not strong enough to keep the large particles suspended. The system is failing to maintain a uniform mix.

This Fluidized Bed DEM Rocky-Fluent simulation provides direct instructions for improving the machine.

Figure 3: The particle mass distribution contours from the DEM Rocky analysis. The image compares the location of small particles (blue) versus large particles (orange) to reveal segregation patterns.