DPM velocity and mass flow
 

Hi,

I am new to DPM and I have a few questions after looking at some comments and tutorials. I hope any of you can help me out.

1. DPM velocity magnitude and total mass flowrate are different from the velocity under Velocity-Inlet and mass flowrate under Mass-Flow-Inlet under Boundary Conditions. Am I correct?

2. What Boundary Conditions should I select for my inlet that will have DPM injection and why? I saw some people using mass-flow-inlet and most using velocity-inlet.

3a. If I select mass-flow-inlet under Boundary Conditions, should I set the value for mass flowrate the same as the value of total mass flowrate under DPM?

3b. If I select velocity-inlet under Boundary Conditions, should I set the value for velocity the same as the value of velocity magnitude under DPM?

Thank you very much.

Hi there


DPM can be a bit confusing and I am no expert, but I can give it a go.


1) Yes, you are correct. The velocity and mass flow rate given for the DPM injection is only for the particles.


2) Either velocity inlet or mass flow inlet is fine - not much difference if the flow is incompressible.


3) This depends on what you are trying to solve. For the mass flow rate, generally no. This would give you the same mass flow of particles as your flow of fluid.
For the velocity inlet/DPM velocity, this is usually a thing, as you want your particles to have the same velocity as the fluid flow.


Hope this helps

Hi Vestdam,

Thanks for your reply.

Regarding the first question, it seems that Boundary Conditions (BC) is used to set the continuous properties of fluid flow, where DPM is used to set the initial properties of particles of the fluid flow. Which means the DPM properties will affect the initial velocity/flowrate of particles, but afterward will depends on BC properties. Am I right?

Second, what will happen if I have the same mass flow of particles as my flow of fluid? My mass flowrate will be doubled?

Third, if I want to have 10kg/s of continuous water flow, I will have to set it in BC, while in DPM I will have a very low value for the total mass flowrate? Or I set the 10 kg/s in DPM and use velocity-inlet instead in BC?

Thank you.

Hi,


1) Correct, the velocity of the particles will be affected by the fluid flow.


2) The flow of particles does not by default affect your fluid flow, so yes, the flowrate will be doubled, but it shouldn't affect your results. If you are only interested in the particle trajectories, the flowrate of particles does not really matter - only the size distribution.


3) Again, the mass flow of particles does not affect your fluid flow by default, so the DPM mass flow should not matter, although it does affect the statistical data on the DPM paths.

Hi Vestdam,

Thank you very much for your replies. They really help me a lot in clearing my doubts.