Learning Forum

[Mahsa Asadi]

Hello, I am simulating a cyclone separator with DDPM and RSM methods. I am encountering convergence issues, and floating errors are appearing in my simulation. Regarding the boundary conditions, especially for the inlet, I am unsure which phase to choose. Should I opt for phase 1 (air), phase 2 (particles), or a mixture for the boundary conditions?

Thank you.

 

[Rob]

With DDPM use air only for the inlet and add a surface injection to that face (Injection panel in DPM model). Depending on loading you may want to explore Rocky-Fluent coupling too. 

As a starting point just run flow and DPM particles. Once that's stable you can make it more complicated by turning on DDPM etc. Note, that may result in needing to rerun from scratch as the Eulerian mulitphase model handles the Dense part of DDPM. 

[Mahsa Asadi]

Thank you for your responding
I chose phase 1 (air) for inlet condition, but, all conditions changed to air. when I changed it to a mixture, all conditions changed to a mixture. 

one more question: how can I set up the parcel method?

[Rob]

Yes, but you then set the phase values (there's an arrow next to Mixture when multiphase is on). 

I would leave the parcel method alone for now; it's in the Injection panel for future reference. If you understand what each option means it's a potentially useful tool but as a relative beginner it's a good way to really mess up the model. 

Have a look in the Knowledge section in Search at the top of the page. We added a lot of content to the public side of the system and that may have included some of the cyclone documents. 

[Mahsa Asadi]

Hello and Thank you for your response.
I want to use DDPM with RSM and I understand that it is very hard to converge in this model and RSM is very sensitive to mesh skewness. this is my meshing and the worst part is the connection between the inlet and the body. how can I improve this mesh? I used the sweep and multizone for meshing. 

[Rob]

Yes, that does need fixing. Have a think about why it's happening (sharp angle) and then look at the mesh blocks. Why does the inlet need to be a separate zone to the main body? Sweep etc direction can be axial, tangential or radial in this sort of design. 

Have you done this course?  /courses/index.php/courses/fluids-in-industry/lessons/cyclone-separator/

[Mahsa Asadi]

Hello, yes I have done that course. you mean, it is better to combine the inlet to cyclone body? 
Excuse me, I have no idea how to fix it. I saw in an article to cut the mesh block to solve it, and I did. As you can see in the above picture, nothing changed

 

[Rob]

I'd look at combining blocks to avoid the sharp angle. With the newer methods & solver numerics a well refined poly mesh is usually as good as full hex too. 

[Mahsa Asadi]

Thank you, I have one more question.
for the parcel method, I understood that the parcel size should be smaller than the smallest size of mesh. the particle diameter = 0.002m and density = 2500. the min volume of mesh = 1.1e-10 and I was looking for the parcel diameter. the picture below shows my solution but I understood that the parcel diameter should be less than the particle diameter. Is it possible, it sounds wrong.

[Rob]

Your particles need to be smaller than the cells too: a 2mm particle means your near wall cell ideally wants to be over 1mm thick. Remember, DPM looks at a point mass.