Plastic Cover Effect in Banks Regarding COVID-19
In this project, based on the CFD method and using ANSYS Fluent software, an attempt has been made to simulate virus particles’ release from a patient’s mouth within a bank.
This ANSYS Fluent project includes CFD simulation files and a training movie.
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Coronavirus (Covid 19) is the most prominent human challenge today, and the high transmission rate of this disease is very problematic. Coughing or sneezing of a person with coronavirus in a public space causes the virus to spread in that space and spread to healthy people in that environment. Many public places, such as banks, can drive virus transmission through a person with COVID-19 who carries the coronavirus to a healthy person within a limited and unobstructed distance. In this project, based on the CFD method and using ANSYS Fluent software, an attempt has been made to simulate virus particles’ release from a patient’s mouth within a bank.
The purpose of this study is to investigate the ability of coronavirus particles to spread inside the bank from a bank customer to a healthy bank employee. This simulation process is performed in two different modes. In the first modeling, no cover is located between the client and the bank employee to show the virus’s transmission power. In the second modeling, an attempt is made to make a thin plastic cover between them. The cover should be defined to demonstrate the process of preventing the transmission of virus particles as a barrier. For the present simulation, the discrete phase model (DPM) is used; Because this model allows us to study a mass of particles discretely or bit by bit in a continuously fluid space.
Due to this model’s choice, the virus’s wet particles secreted from the patient’s mouth are considered a discrete phase. The airflow inside the bank’s interior is regarded as a continuous phase. The physical models of discrete particles defined in this simulation include two-way turbulence coupling, meaning two-way interaction between continuous and discrete phases activating the interaction with continuous phase mode. The stochastic collision means irregular droplets colliding with each other, coalescence means droplets merging, and breakup implies the droplets’ collapse. The type of discrete phase behavior will also 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, injection particles are defined as Droplets; Thus, water is defined as droplets, and water vapor is defined as an evaporating gas species. The injection is performed superficially and through the Surface of the patient’s mouth. According to this definition of injection, virus particles from a sick human cough are physically expelled from the patient’s mouth by water droplets evaporating in space. These virus droplets have a temperature of 310 K, a velocity of 32 m.s-1, and a flow rate of 0.018 kg.s-1, emitted at intervals of 0 s to 0.1 s.
The virus particle size during propagation is not constant, and the rosin-rammler-logarithmic distribution method is considered for the diameters’ size. Following this method and following the suitable formulation, the values related to the minimum, maximum and average diameter size determine the exponential parameter of the spread and the number of diameters per injection. It should be noted that the Droplet mode is applied when the species transport model is also activated. In this model, three different gases, including oxygen (O2), nitrogen (N2), and water vapor (H2O) is activated, and thus the computational area of our model will have airflow.
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 people’s bodies and all the walls related to the tables, chairs, and the bank floor have a Trap mode, which means that particles are trapped and accumulate on these surfaces. The present simulation process is performed unsteady and in a time interval for 0.5s with time steps equal to 0.0025 s.
Geometry & Mesh
We design the present model in three dimensions using Design Modeler software. The model’s geometry includes a computational domain of the interior of a bank that includes a table, two chairs, and two people. In this modeling, one of the two humans is a sick person. We defined him as the virus’s source via cough. We assume the mouth as the reference surface of the discrete phase virus release in this model. In this simulation, two different geometric models are designed including a case with no plastic cover, and another case considering a thin plastic cover located between two people on the table.
We use ANSYS Meshing software for the meshing of the model. The mesh type is unstructured and the element numbers are 1570219 and1618366 for the first case (without plastic cover) and the second case (considering plastic cover), respectively. The following figure shows the mesh.
Plastic Cover Effect in Bank CFD Simulation
We consider several assumptions to simulate the present model:
- We perform a pressure-based solver.
- The purpose of the problem is virus particle tracking over time, so the simulation is unsteady.
- 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|
|Species model||Species Transport|
|number of volumetric species||3 (H2O,O2,N2)|
|Discrete phase model||On|
|interaction||interaction with continuous phase|
|particle treatment||unsteady particle tracking|
|physical models||two-way turbulence coupling|
|release from surfaces||inlet-mouth|
|point properties||temperature||310 K|
|total flow rate||0.018 kg.s-1|
|Walls of Floor, Men, Chairs, Desk||Wall|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|discrete phase conditions||trap|
|Mouth of Man||Wall|
|wall motion||stationary wall|
|heat flux||0 W.m-2|
|discrete phase conditions||escape|
|momentum||first order upwind|
|H2O||first order upwind|
|O2||first order upwind|
|energy||first order upwind|
Plastic Cover Results
At the end of the solution process, we obtain particle tracking of the virus particles at different time intervals of the simulation process. This particle sequence is based on the residence time of the particles and the particle diameter size. We perform this simulation process in two modes with and without the plastic cover. The effect of plastic cover in preventing coronavirus dispersion is evident from the results.
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.