The Coronavirus Spread (COVID-19) is a major global health problem. The virus moves from person to person through tiny water drops called droplets and aerosols. When a sick person coughs or sneezes, they release thousands of these particles. Large drops fall to the floor quickly, but small aerosols can float in the air for hours. This is called airborne dispersion. Understanding how these particles move in a room is critical for safety. Real experiments with viruses are dangerous and hard to do. Therefore, engineers use CFD simulation to test indoor safety on a computer. We use ANSYS Fluent to model the invisible movement of air and droplets. This software helps us see if the ventilation system is good enough to remove the virus.

In this report, we perform a detailed CFD Analysis of Coronavirus Spread. We simulate a sneezing event in a standard room. We use the Discrete Phase Model (DPM) to track individual drops. We also use advanced physics like evaporation and breakup models. This aerosol Dispersion CFD study helps architects and doctors design safer hospital rooms and offices. For more details on air systems, please explore our HVAC Simulation tutorials: https://cfdland.com/product-category/application/hvac-cfd-simulation/

• Reference [1]: Dbouk, Talib, and Dimitris Drikakis. “On coughing and airborne droplet transmission to humans.” Physics of Fluids5 (2020).
• Reference [2]: Mesgarpour, Mehrdad, et al. “Prediction of the spread of Corona-virus carrying droplets in a bus-A computational based artificial intelligence approach.” Journal of Hazardous Materials413 (2021): 125358.

Figure 1: Saliva droplet cloud kinematics illustrating the diameter distribution of droplets resulting from a human cough or sneeze event [1].

Simulation Process: Room Mesh and DPM Physics Setup

For this Coronavirus Spread CFD simulation, we designed a realistic room. We placed a simplified human model in the corner to mimic a patient. We generated a high-quality mesh using 423,011 polyhedral cells. Polyhedral cells are very accurate for Indoor Environment Ventilation because they capture swirling air patterns better than other mesh types. We refined the mesh near the human’s head and the walls to catch small details. We set the ventilation inlet velocity to 2.4 m/s to supply fresh air. We used a Transient Solver in ANSYS Fluent because a sneeze happens very fast.

To model the sneeze realistically, we used a custom UDF code (User-Defined Function) in C language. This code injects droplets from the mouth over 0.1 seconds. The droplets range in size. We used the Discrete Phase Model (DPM) with 2-way coupling. This means the air moves the drops, and the drops affect the air. We enabled the TAB Breakup model to simulate how large drops break into smaller ones due to air pressure. We also used the Saffman Lift Force to calculate how drops move near walls. Finally, we turned on the Evaporation Model to calculate how droplets shrink and become dangerous aerosols. This setup ensures the Virus Spread fluent simulation is physically correct.

Figure 2: 3D Room Geometry model design showing the location of the human figure, the ceiling ventilation inlet, and the room

Post-processing: Aerosol Trajectory and Ventilation Analysis

This section analyzes the engineering data to understand how the virus spreads. We examine the contours and particle tracks to evaluate the risk of infection in the room. First, we analyze the airflow patterns in Figure 3. The pathlines show that the fresh air enters at 2.45 m/s and creates a large circulation loop in the center of the room. However, near the human in the corner, the velocity is low (0.24 to 0.73 m/s). This is a critical finding. It means the air is “stagnant” or slow-moving near the patient. This slow air allows the aerosol Dispersion to linger near the source before the ventilation removes it. This increases the risk for anyone standing nearby.

Next, we evaluate the spread of the virus over time using Figure 4. At time T1 (0.1 seconds), the droplets are in a tight red cloud near the mouth. This is the “ballistic” phase where the sneeze velocity (50-100 m/s) dominates. By time T3 and T4 (3 seconds), we see a clear separation. The large droplets fall quickly to the floor due to gravity. The simulation confirms that within 3 seconds, the heavy particles have contaminated the ground surfaces. However, the small aerosols remain floating. These particles have travelled across the entire room volume. This proves that Coronavirus Spread is not limited to 2 meters; the ventilation carries the virus to the opposite wall.

Figure 3: Pathlines colored by velocity magnitude, visualizing the complex airflow recirculation patterns and the high-speed air jet entering from the ceiling inlet.

Figure 4: Four time snapshots (T1, T2, T3, T4) of particle residence time, showing the progression of the Coronavirus Spread from the initial sneeze burst to full room dispersion.

Finally, we look at the physics of the droplets in Figure 5 and Figure 6. The velocity contour shows that falling droplets reach a terminal velocity of 0.6 to 0.8 m/s. The evaporation contour in Figure 6 is very important. It shows high evaporation rates (1.14e-05 kg/s) right after the sneeze. Benefit to Designer: This data confirms that droplets are shrinking rapidly. As they shrink, they become lighter and stay in the air longer. The ANSYS Fluent results warn us that high evaporation creates more airborne nuclei. The simulation proves that a 2.4 m/s ventilation rate helps dilute the cloud, but the strong circulation loops can also spread the virus to clean zones of the room before exhausting it.

Figure 5: Particle velocity contours near the ground, distinguishing between fast-falling heavy droplets and slow-moving airborne aerosols.

Figure 6: DPM Evaporation rate contours showing how droplets lose mass and shrink due to phase change immediately after leaving the mouth.