Operating Room: COVID-19 Breathing, Transient Solver

COVID-19 Patient Transient Breathing in the Operating Room, ANSYS Fluent Training

Description

This project simulates transient breathing airflow from a COVID-19 patient's mouth within an operating room using ANSYS Fluent. The operating room is equipped with ventilation and air conditioning systems, and the patient continuously inhales oxygen and exhales carbon dioxide throughout the simulation. The primary objective is to evaluate how effectively fresh, oxygen-carrying air continuously flows into the room's interior, diluting and displacing contaminated exhaled air from the patient's mouth rather than allowing it to accumulate.

Ventilation and air conditioning systems positioned on the room's ceiling and floor circulate fresh air throughout the interior, directing it out through side vents to the exterior. The room is modeled as a cubic space measuring 2.9 m × 2.23 m × 3.7 m, containing a hospital bed and patient, with six circular fresh air inlets and five rectangular outlet vents positioned along the side walls.

The 3D geometry was designed in Design Modeler, with the patient's oral surface defined as the inlet boundary, since the primary focus is the exhaled airflow from the patient's mouth. The domain was meshed in ANSYS Meshing using an unstructured grid totaling 4,354,238 elements, with finer mesh resolution applied near internal boundaries to improve accuracy. Given the time-dependent nature of respiration, the simulation was run as unsteady with a time step of 0.01 s.

Methodology

The incoming fresh air consists of oxygen and nitrogen in a 3.76 ratio, while the patient's exhaled air additionally contains carbon dioxide — requiring the Species Transport model to track these species throughout the domain. Fresh air entering through the room's air conditioning system carries an oxygen mass fraction of 0.23 and nitrogen mass fraction of 0.77, with no carbon dioxide, entering at 1 m/s and 293.15 K.

Since the exhaled airflow from the patient's mouth acts as a discrete source of gaseous species, the Discrete Phase Model (DPM) was used to track these particles from a Lagrangian perspective. Exhaled air was defined with an oxygen mass fraction of 0.16, a carbon dioxide mass fraction of 0.04, and a temperature of 310.15 K.

Since real breathing involves inhaling and exhaling through the same oral opening, a custom UDF defined the mouth's airflow velocity as alternating between positive (exhalation, air leaving the mouth) and negative (inhalation, air entering the mouth) every 2.5 seconds, with a velocity magnitude of 0.25 m/s throughout.

Conclusion

By tracking the exhaled particles — oxygen, nitrogen, and carbon dioxide — using unsteady DPM particle tracking, this simulation captures how airborne particles exhaled from the patient's mouth behave and disperse over time within the operating room. This approach enables a detailed, time-resolved analysis of coronavirus particle dispersion inside the operating room under the influence of the installed ventilation and air conditioning systems — directly informing infection control strategy for clinical settings during patient care.