The air inside our offices is very important for our health. Dust and small dirt particles can come in through open windows. Once inside, the ventilation system moves them around. It is hard to see these tiny particles with our eyes. To understand where they go, engineers use computer simulation. Particles Surface Injection is a method used to model how dust enters a room.

This project is a Particles Surface Injection CFD simulation designed to teach you how to track dust. We use ANSYS Fluent and the Discrete Phase Model (DPM) to see the path of the dust. By simulating this DPM Surface Injection, we can find out where the dirty air stays the longest. For more lessons on particle tracking, please visit our DPM tutorials.

Simulation Process: Modeling the Surface Injection DPM CFD Simulation

To start this DPM CFD simulation, we built a 3D model of an office with two rooms. The most important step was setting up the particle injection. In ANSYS Fluent, we selected the “Surface Injection” type. This means the computer releases thousands of particles from the face of the window, just like real dust blowing inside.

We did not use particles of only one size. Real dust comes in many sizes. So, we used a Rosin-Rammler distribution. This is a mathematical formula that creates a mix of particle sizes. In this study, the particles ranged from 1e−6 meters to 1e−5 meters. We also used “unsteady tracking.” This allows us to see how the particles move over time, second by second. The goal of this Particles Surface Injection Simulation is to calculate the residence time, which means how long a particle floats in the room before leaving.

Figure 1: The office geometry showing the window where particles enter.

Post-processing: Detailed Analysis of Particle Tracks and Time

A real analysis of the simulation results helps us understand indoor air quality. The most critical result is the Residence Time. The colored lines in the simulation show the path of each particle. The color bar tells us the time in seconds. The data shows that many particles do not leave the room quickly. Some particles stay trapped in the office for up to 55 seconds. This is a long time for dust to float around. This happens because of the airflow patterns. When the air comes in from the window, it hits walls and furniture. This collision creates recirculation zones or spinning pockets of air.

The DPM Surface Injection ANSYS fluent results clearly show these zones. In the corners of the room and behind furniture, the air spins in circles instead of flowing to the exit. The particles get caught in these spins. The simulation tracks prove that the particles in the center of the room move fast and exit quickly. But the particles near the walls get stuck in the slow-moving air. This is why the residence time reaches 55 seconds in those specific spots. This analysis proves that the shape of the room and the furniture placement directly affect how long we breathe dirty air. The “unsteady tracking” allows us to see this trapping effect happen in real-time simulation steps. This confirms that simple ventilation is not always enough to clear out the corners of a room.

Figure 2: Particle residence time after the surface injection inside the office

Figure 3: Particle tracks colored by residence time, showing trapping up to 55 seconds.

Key Takeaways & FAQ

• Q: What is DPM Surface Injection?
  • A: It is a method in ANSYS Fluent where particles are released from a specific surface, like a window or inlet. In this Particles Surface Injection CFD simulation, it mimics dust blowing into a room.
• Q: Why is residence time important?
  • A: Residence time tells us how long a particle stays in the room. A high time, like the 55 seconds seen here, means the ventilation is not removing the dust efficiently.
• Q: What is the Rosin-Rammler distribution?
  • A: It is a way to model a realistic range of particle sizes. Instead of all particles being the same size, we simulated diameters from 1e−6 to 1e−5 meters.