## Fluids

#### Simulate breathing from a surface parameters

• HusseinK
Subscriber

Dears,

I hope you are doing fantastic

I am simulating a 3D room with people inside it using Fluent, I am trying to simulate the process of breathing inside the room.

Does anyone know what is the correct way to simulate the respiration process? whether to use inlet velocity BC on the surface that represents the mouth? or use mass flow inlets/outlets?

The design has two models inside where both are breathing and one of them is infected and I want to see whether the distance between them is enough or not.

I am also using (Injections) from the surface of the infected person but I am not quite sure if it is the right approach.

Any help would be greatly appreciated.

Thanks and stay safe.

• Rob
Ansys Employee
Velocity boundary with a transient profile works well, as you can switch the direction of flow. Or source terms if you don't want to include the dummy (person) in the model. DPM is also a commonly used approach. To an extent it's down to what you want to investigate. Have a look at some of the work by Bert Blocken using Fluent on Covid spread and the various models here https://www.ansys.com/en-gb/covid-19-simulation-insights
• HusseinK
Subscriber
Really appreciate it rob.

So the scenario is a teacher and few students in a classroom.
Initially I want to set the teacher as the infected person and want to see whether the student will be affected or not.
1- teacher mouth has inlet velocity with injections at the same surface of (nitrogen) material.
2- students mouth will be a wall with (trap) DPM BC.

Does this sounds right?
I am sorry if the questions seems ignorant at the beginning.
• Rob
Ansys Employee
You're here to learn, so no such thing as a daft question. Well, there are a few, but this isn't one of them.
It's a reasonable set up. I suggest altering the breathing rate(s) to run as steady state to start with otherwise you'll need a transient calculation which significantly increases the model run time. Steady will work/fail much more quickly so is better when learning, and more generally when you don't want to wait for a few days for an answer.
Read up on the particle summary options, and DPM out files: or set the mouths as trap and walls/floor/room ventilation as escape. You want to know how many particles are inhaled, and if you use a size distribution how much mass.
• HusseinK
Subscriber
Super, thank you a bunch.

One more quick question:
For a certain surface (mouth) with injection assigned to it and inert particle defined (Diameter, Temp, velocity), do we need to set the same velocity in the boundary condition tab for the same surface (mouth)?

Thanks again Rob!
• Rob
Ansys Employee
You don't as the flow will accelerate the particles, so it's more a question of what you want to happen. Given injection settings are harder to adjust I'd leave it as a fixed (zero) value in your case.