Learning Forum

[Narges]

I'm trying to calculate DPM erosion Rate, but no matter what method I use, I just get zero as the result! can anyone help about what the problem is from?

System: fluid + nanoparticles are injected from the inlet of the microchannel

I used: 3D-dp-pbns-steady state flow

viscose model: SST k-omega

DPM: 2-way coupled, injection type: surface-inlet

BC: velocity-inlet, pressure-outlet, reflect-wall

[DrAmine]

Are you using the Boundary Trap for DPM at the walls?

[Narges]

I have used "reflect" and "wall-jet" and also "trap" and even UDF! not only Erosion rate, but also the "DPM wall force" and "DPM wall normal pressure" are zero!
my fluid is Water. I resimulated my system with air and it worked! how can I solve it?

[DrAmine]

Please first focus on using Trap and check if any particles are declared to be trapped? Which version area you using?

[Narges]

I'm using Student version. when I change my fluid from "liquid water" to "air" I can get non-zero value. but I don't know how to do it with liquid Water.

[DrAmine]

The same way as with air: your particles are not hitting any wall perhaps..

[Narges]

This is the geometry of my microchannel. with 3m/s velocity and 0.5mm distance of inlet and wall, collision is inevitable. is there anything that I can do to resolve it?

[DrAmine]

Also again: if you set the wall to be a trapping wall: do you see the particle trapped there Yes or No?

[Narges]

when I use water as fluid there is no trapped particle.
when I use Air as fluid, less than a third of particles are trapped and else escaped.

[DrAmine]

If you do not have any trapped particles then you won't see any erosion rate as your particles are not toughing the wall. Please add a screenshot of particle tracks and screenshot of particle DPM Summary.

[Narges]

Dear Dr. Amine this is my system mesh from inlet to the spherical wall:
and this is the particle track:
and this is the summery of tracking:
could the problem be from my meshing?

[DrAmine]

The mesh does not look good for me but it is my flavor as I prefer uniform mesh and boundary layer resolved meshes. Moreover your particles are all escaping so your erosion rate will be zero. You said at it was air particles are trapped on the wall. Water has higher viscosity and this will affect the particle relaxation time. Can you estimate the Stokes number based on the properties you have?
Consider changing the position of the outlet to avoid any numerical backflow which you are now just "avoiding" via artificial wall creation.

[Narges]

Dr. Amine, thank you for your answer. the Stocks number is 1.8575e-6 for this system.
sorry, but I didn't get the "changing the position of the outlet". how can I do that?

[DrAmine]

you place your outlet bit more downstream to avoid any numerical backflow. Sometimes backflow will also happen due to the physics. Please disable the "prevent backflow" option and try to figure out why you have a backflow.

Your Stokes number is very low so the particles will be like passive tracers and travel with the flow.

[Narges]

Thank you very much for your help. with increasing the particle relaxation time I can get non-zero wall force. I also I removed the "prevent backflow" option.
would you please suggest me a method to improve my meshing?

[Rob]

likes inflation and hex, alternatively have a look at Fluent Meshing and use inflation with polyhedral cells.
With a Stokes Number that low I'd be surprised if the particles hit anything: they'll follow the flow.

[DrAmine]

Assess some inflations layers :)

[Narges]

thank you . sure, I will do that