## Fluids

#### DPM, postprocessing

• Abdelrahman92
Subscriber

I am tracking particles falling in stagnant fluid using DPM. I am interested in particle velocity as  a function of time (and terminal velocity). I have two questions:

(1) In the attached d picture, the x axis (time), is it the solver calculation time or the actual time that the particle spend in the column ?

(2) As I said I want to see the change of the velocity with time (as the particle settle down the column), the trend should start with unsteady velocity and finally reach steady state terminal velocity.

My Q: Should I use unsteady tracking ? I tried using steady uncoupled tracking (attached picture)

Thanks

• Abdelrahman92
Subscriber

• Rob
Ansys Employee

Can you post an image of the Particle tracking panel? From memory the default is particle residence time but hard to know without looking at what you set.

• Abdelrahman92
Subscriber

plz see attached

• Rob
Ansys Employee

Assuming the model is steady that's probably particle residence time, and it looks to accelerate up very quickly from the injection. Try plotting velocity against path length.

• Abdelrahman92
Subscriber
Could you explain to me what is exactly the difference between steady and unsteady tracking?. I have read this section from the manual, but it is still confusing. For DPM, fluent solves the ODE (particle motion equation), which is by nature time dependent (dv/dt). So steady state tracking should give the v(t).
What would you suggest for my case, steady or unsteady ? (Remember I am interested in the change of the velocity with time
• Rob
Ansys Employee

Steady should work as the particles are travelling though the domain and not altering the flow.

• Abdelrahman92
Subscriber

I expect to get two distinguished regions for the velocity profile (steady and unsteady) as the attached picture. However, what I got (previous pictures) is a sudden increase in the velocity to a constant value (most probably the terminal).

This case is very simple: I am using uncoupled tracking with no interaction with the continuous phase. The geometry is 2D cylinder has only inlet (zero velocity specified for the inlet continues phase) and the rest is wall. Recently I tried a geometry with only walls. In both case I initialized & patch the domain with zero velocity since the fluid Is stagnant

Could let me know what is most probably casing the issue with my results ??