Learning Forum

[sapkotadpak]

Hi, I am simulating rotating cylinder (10rpm) which has 2 micrometer particles and air inside it. I have altogether 1000 particles and I would like to know how much particles deposit in the wall in each 30 minutes. Could you please tell me how to do this on fluent? I am using dpm model, flow assuming steady state , one way coupling.

[Rob]

If it's steady state then you can use a DPM out file (DPM Summary) to find the flight time of all particles. You'll need to sort the data to see what arrives at the wall in each period of interest. 

[sapkotadpak]

Hi yes its a steady state. How can I get the fligh time? I don't see anything in the console? For smaller particles it might take hours to deposit. How do I simulate it?

Because of gravity the problem isn't axisymetric. The fluid is less affected by gravity and can be ignored. But particles are affetced by gravity. How can I include gravitational force only in the particle trajectory calculations?

[sapkotadpak]

Do you have any examples/tutorials on flow inside the rotating cavity? I see a lot of materials on flow outside the rotating cylinder but not on this one.

[sapkotadpak]

How do you determine if your flow is Laminar or turbulent due to rotation only? 

[Rob]

If the fluid density is constant then gravity won't do anything other than at pressure flow boundaries. 

Have a look at the DPM Summary tools, Results>Reports. I don't think there are any specific tutorials, but have a look at the cyclone examples for some ideas. 

You need to decide if it's laminar or turbulent - have you looked for a Reynolds Number definition for this sort of flow? 

[sapkotadpak]

When I click on the discrete phase> summary is turned off. Do you think its better to use 2d axisymmetric condition by turning of gravity? Can I add gravitational force to particle later?

The rotational reynolds number is 180 =(omega^2*r/kin. viscosity) but not sure whether its laminar or turbulent. 

Can my simulation give the data of deposition percentage of particle after 4/5/6 hours of rotation?

For the rotation, should I apply rotational motion to  absolute or relative to adjacent cell zone? 

What is the rotation axis origin? Is is the coordinates of center of my cylinder?

 

[Rob]

The centre of rotation is the vessel axis, and the origin will be at one end or the other. It's a vector so if you don't quite get the ends right it's fine, but you must make sure it's on the axis. 

2d means no gravity, well other than along the axis. That may or may not be suitable. Or you can use 2d and model a cross section. 

Add the particles to the domain, set the wall as trap and you should be able to record when the particles hit the wall, and where. Summary should work uncoupled, but check that. 

[sapkotadpak]

Can gravitational force be added to particles later as a body force? 

When I turn on the dpm, and track particles and report it on console, I get no of particles trapped, no of incomplete particles. I get the min and max time elapsed, average and std dev. But I dont see the time at which each particle hit the wall. How can I get that?

If I wanna no the particles fate after longer time, should I simply change the max number of steps or is there a way to change the time tracked?

[Rob]

Incomplete means they're not reaching the "end" of their trajectory. End would typically be an "escape" or "trap" - left domain or stuck to a surface and removed respectively.  

Yes, you may want to increase the maximum number of steps, but I'd display some tracks first to see what's actually happening.