Learning Forum

[Gerald Gallagher]

Hi,

I am attempting to simulate a sphere settling under gravity in a viscous fluid (water for now) using the Macroscopic Particle Method (MPM) in Fluent 2023 R1.

I managed to set up a sphere falling in air by watching a good video posted on a YouTube channel mentioned in the CFD Online thread https://www.cfd-online.com/Forums/fluent/33104-macroscopic-particle-model-mpm.html:

https://youtu.be/bGU62t9DDy0

I tried to set up spheres falling in water with steps from another video posted on the same YouTube channel:

https://youtu.be/920ajl_nV68

However, the spheres either don't move or the behaviour is unphysical. Also, the continuity residuals are very large. The geometry I use is very similar; it is slightly simplified to be just a rectangular box without the reduction in size in the middle of the domain, but uses the same overall dimensions from the video. The mesh I am using has very similarly sized tetrahedral elements as well. I am following the steps as closely as possible, but I still cannot replicate the behaviour from the video.

I should note that I had to replace the animation setup from the videos with the more current "scene" setup.

Would anybody have any advice on this issue?

Thanks!

[Rob]

What material is the MPM particle defined as? 

[Gerald Gallagher]

Hi Rob,

Thanks for your reply.

I set the particle density to 1100 kg/m3 and diameter as 0.02 m in the MPM setup window as per the video. In the standard Fluent Materials section, "aluminium" is set as the material for "Solid" and I change the density to 1100 kg/m3 as per the video. The material "anthracite" is set as the material for "Inert Particle" and I change the density there to 1100 kg/m3 as per the video.

It did seem strange that I should have to change the density in multiple places to the density of the particle. Is there anything that I am doing incorrectly?

Thanks

[Rob]

I've not used the model since it was a UDF function: it has a use but for dropping objects we tend to favour moving mesh or DEM now. I suspect the DPM part is because of the way the model works, no idea about why you'd need to alter the solid material.