Covid-19: Consideration for Wearing Shields
In this project, based on the CFD method and using ANSYS Fluent software, an attempt has been made to simulate the release of coronavirus particles from the mouth of a patient while talking and using a shield to prevent the transmission to another person.
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Coronavirus (Covid 19) is known as the biggest human challenge in the world and the high transmission rate of this disease is very problematic. One of the most important recommendations of doctors regarding the prevention of disease transmission between people is the use of special masks or shields in low social distances. In this project, based on the CFD method and using ANSYS Fluent software, an attempt has been made to simulate the release of coronavirus particles from the mouth of a patient while talking and using a shield to prevent the transmission to another person.
The aim of this study was to evaluate the effectiveness of using a shield or mask as a barrier on the face of a patient against the spread of virus particles. For the present simulation, the discrete phase model (DPM) is used; Because this model allows us to study the particles mass discretely in a fluid space with continuous phase . Due to the choice of this model, the virus particles secreted from the patient’s mouth are considered as a discrete phase and the open air flow in the computational area is considered as a continuous phase. The type of discrete phase behavior will be time dependent 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, which determines the type and quality of discrete particles injected into the model. In this model, the emitted particles are defined as 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 flow rate of coronavirus particles exiting the mouth. In fact, this profile shows the amount of velocity and diffusion of emitted particles when speaking.
In this way, these virus particles are removed from the patient’s mouth in a time-dependent 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 defined by a specific ratio to the particle velocity. Also, the boundary conditions related to the discrete phase model are defined in such a way that the particles in the boundary related to the patient’s mouth have a Escape state, meaning that the particles pass through this boundary. Masks or shields mounted on the patient’s face have a Trap mode, which means that particles are trapped and accumulate in these boundaries.
The present simulation process has been performed Unsteady for a period of 40 s with a time step equal to 0.05 s.
Shield Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. The geometry consists of a computational domain measuring 1.6 m * 2 m * 2.6 m in which two humans 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 surface of the patient’s human mouth is differentiated by the Mouth boundary condition; Because this boundary is assumed as the reference surface of discrete phase virus release. On the other hand, a shield is drawn on the face of the patient person as a barrier.
The meshing of the model has been done using ANSYS Meshing software, and the mesh type is unstructured. The element number is 724043. The following figure shows the mesh.
Using Shield CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The simulation is transient, because the purpose of the problem is to particle tracking 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 and shield||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 solution process, the particle tracking of the virus particles at different time intervals of the simulation process is obtained. This particle sequence is based on the Residence Time and the velocity of the particles. As can be seen from the images, and according to the simulation process defined, the virus particles are expelled in periodic from, from the patient’s mouth in 20 s. According to the pictures, it can be concluded that the presence of a shield causes the virus particles to come out of the patient’s mouth to accumulate on the shield and not be transmitted to a healthy person.
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.