## Fluids

#### How to get the number of particles in a defined area (volume) for each time step in fluent?

• mdislam
Subscriber

I am trying to do a CFD analysis of number of particles inhaled by a person based on a DPM injection. However, it seems simulation of inhalation is not a straightforward approach. So, as an alternative I am planning to define a volume in front of the face and collect the number of particles which are passing by that area each time step. Can anyone suggest me how I can do this? I am not sure whether it is a good approach or not. Or you feel there is some better alternatives to do the same? It would be a great help to have your suggestions.

• Rob
Ansys Employee
How much of the mouth/throat are you modelling? How is the model "breathing"?
• mdislam
Subscriber
If I say that I am modeling "breathing" then it would be a wrong statement. Simulation of breathing will make the model really computationally heavy due to continuous changing boundary conditions from inlet(exhale) to outlet (inhale). To avoid complications, I am thinking about defining a volume ( let's say a sphere/cube) in front of the face and collect the number of particles which are passing by that area each time step. My question is,
How to define that sphere / cube in fluent in front of the face? Can I define that using the regular graphical user interface of Ansys fluent? Or do I need to define a UDF to do so?
If I can define the sphere/cube in front of the face, what will be the UDF to collect the number of particles (parcels) present on that sphere/cube at a certain time step. For example, if I get 10 particles present at time t in front of the face, then I can define some probability like X out of 10 particles will be inhaled by the person at time t+1. Can someone guide me how I can achieve that or are there any different approach which should i try?
• Rob
Ansys Employee
A not unreasonable solution. Have a look at the DPM Summary options. However, that will also count particles multiple times if they pass back and forwards through the zone.
• mdislam
Subscriber
Thank you Rob! In DPM summary report it only shows the number of particles (parcels) at the end of the simulation. But it doesn't show any particle report for all the timesteps. How I can achieve this? Also, is there any easy way to define an area in front of the face?
• DrAmine
Ansys Employee
Do dpm sampling on a plane in that region and it will write fole of all particles going through the plane .
• lydau
Subscriber
How did you model the nose/mouth of the person? If its simplified as a surface (circular or square), define that as an outlet boundary and count the amount of particles leaving the domain through the outlet at each timestep. A number of previous publications in indoor air quality use this approach. Have a look at this recently published paper: Coldrick, S., Kelsey, A., Ivings, M. J., Foat, T. G., Parker, S. T., Noakes, C. J., ... & Moore, G. (2022). Modeling and experimental study of dispersion and deposition of respiratory emissions with implications for disease transmission.Indoor air,32(2), e13000.
Hope it helps!
• DrAmine
Ansys Employee
Nice.
• prashantha
Subscriber
I stucked in the DPM modeling by adding fixed count of particles at the inlet.
using particle number in the parcel by injection, but its not adding fixed count of particles at inlet.
You could help me with this.