## Fluids

#### Cough particle simulation

• Lo Jaclyn
Subscriber

Hi, I am modeling the dispersion of cough droplets in a room with two velocity inlets (velocity=1.68m/s) and one pressure outlet at 0 gauge pressure. The droplets shall be injected from a surface on the occupants' mouth for 0.4s. I would like to observe the particle trajectories and get to know how many particles remain in the room. Currently running on steady-state.
Below are the setup of my model. May I ask if this context involves multiphase modeling and species transport?

Models:
Energy= on,
viscous= k-epsilon, RNG, Standard Wall functions,
Discrete phase=on (the other models are off)

Discrete Phase:
Interaction with continuous phase, unsteady particle tracking
Injection= surface,
particle time step size=0.001,
no. of time steps =1,
physical model=saffman lift force
particle type= inert,
material= water liquid,
diameter distribution= uniform.
injection velocity= 10 m/s, temp= 37 C, start time =0 stop time= 0.4 secs, flow rate= 1e-20, diameter= 0.0001m, scale flow rate by face area,
drag law: stokes-cunningham, brownian motion ticked,
discrete random walk model, time scale constant=0.15,
parcel release method: standard

And the results only show a streamline, how can I visualize the dispersion/concentration of the particles inside the room?

Would really appreciate it if someone could provide some advice on the setup or point out my mistake if there are any as I got confused going through the tutorial...Thank you!

• Rob
Ansys Employee

OK, have a careful think about what you want.

A cough is a transient event, but how far do you expect the "pulse" to travel, and for how long a duration will it move. Does that effect the overall room flow, do you need to include that effect in the model?

Particles tracked as "transient" will display as points (default) which tend to be near enough invisible. Have a look at spheres and scaling factors.

Multiphase is a fun area: DrAmine and I have a fair bit of experience in that area. We (Ansys) sometimes split DPM from "multiphase" for historic reasons. Read the Theory Guide, and also look carefully at the range of the models and limitations.