Talking Spread COVID-19, CFD Simulation
This study aims to investigate the ability of coronavirus particles to propagate at a distance less than a social distance via talking.
This ANSYS Fluent project includes CFD simulation files and a training movie.
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Coronavirus (Covid-19) is known as the most significant human challenge in the world today, and the high transmission rate of this disease is very problematic. One of the doctors’ essential advice regarding preventing the transmission of the disease between people is maintaining the social distance between people when talking to each other. In this project, based on the CFD method and using ANSYS Fluent software, an attempt has been made to simulate the release of virus particles from a Coronavirus patient’s mouth while talking and transmitting it to another person in an specific space. This study aims to investigate the ability of virus particles to propagate and transmit at a distance less than a social distance.
For the present simulation, the discrete phase model (DPM) is used; Because this model allows us to study a mass of particles discretely in a continuously fluid space. Due to this model’s choice, the virus particles secreted from the patient’s mouth are considered a discrete phase. The open airflow in the computational area is regarded as a continuous phase. The type of discrete phase behavior will be time-dependent and with a time step of 0.001 s (by activating the unsteady particle tracking mode). After activating the discrete phase model, the Injection process must be defined, determining the type and quality of discrete particles injected into the model.
In this model, the emitted particles are defined as the Inert type, and the injection type is Surface and is done through the surface of the patient’s mouth. These virus particles have a constant diameter of 0.000001 m and a temperature of 310 K, which are spread between 0 s and 20 s. A specific Profile has been used to define the velocity and mass flow rate of virus particles. This profile shows the velocity and flow rate of the emitted particles when speaking; Thus, these virus particles are removed from the patient’s mouth in a Transient manner. The particle velocity profile is defined as a sinusoidal function with a maximum velocity of 0.33 m.s-1, and the particle flow rate is determined by a specific ratio to the particle velocity.
Also, the boundary conditions related to the discrete phase model are defined as particles at the patient’s mouth boundary with Escape mode, which means particles passing through this boundary. At the boundaries of both the body and the floor with Trap mode means particles are trapped and accumulate at these boundaries. The present simulation process has been performed unsteady state for 40 s with a time step equal to 0.05 s.
Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. The model’s geometry includes a computational space measuring 1.6 m * 2 m * 2.6 m in which two people are facing each other at a distance of 80 cm. One of these two people is designed as a patient; So that the patient’s mouth is defined as the source of the spread of the virus caused by talking. Hence, the patient’s human mouth’s surface is differentiated by the Mouth boundary condition; Because this level is assumed as the reference surface of discrete phase virus release in this model.
We carry out the meshing of the model using ANSYS Meshing software, and the mesh type is unstructured. The element number is 724076. The following figure shows the mesh.
CFD Simulation Settings
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is unsteady, since the purpose of the problem is the particle tracking related to the discrete phase over time.
- The gravity effect on the fluid is equal to -9.81 m.s-2 along the Z-axis.
The following table represents a summary of the defining steps of the problem and its solution:
|near-wall treatment||standard wall function|
|Discrete phase model||On|
|particle treatment||unsteady particle tracking|
|release from surfaces||inlet-mouth|
|point properties||diameter||0.000001 m|
|total flow rate||profile|
|pressure gauge||0 Pascal|
|backflow total temperature||300 K|
|discrete phase conditions||escape|
|discrete phase conditions||escape|
|Floor and Bodies||Wall|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|discrete phase conditions||trap|
|momentum||first order upwind|
|turbulent kinetic energy||first order upwind|
|turbulent dissipation rate||first order upwind|
|energy||first order upwind|
|Gauge pressure||0 Pascal|
|velocity magnitude||0 m.s-1|
At the end of the dissolution process, we obtain the particle tracking of the virus particles at different time intervals of the simulation process. This particle sequence is based on the residence time and the velocity of the particles. According to the simulation results, the virus particles expelled from the patient’s mouth in the first 20 s. In the second 20 s, only the particles in the space between the patient and the healthy person continue their transitional movement. According to the results, we conclude that by talking to the patient without mask or shield for 20 s, these virus particles transmit to a healthy person after 40 s and expose him to receiving virus particles.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, the Training File presents how to solve the problem and extract all desired results.