Effect On Particle Due to Fluid Density Change
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- This topic has 5 replies, 3 voices, and was last updated 3 months, 3 weeks ago by Christoph.
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January 8, 2024 at 8:07 pm #8111JijoParticipant
Hello OpenLB community,
I am currently working on thermally heated resolved particles.I have been investigating whether these particles are influenced by changes in fluid density, particularly in relation to the Boussinesq approximation. I experimented with such test case but I can not notice any effect on the particle’s velocity when including this effect. Any idea on such scenario?
Regards,
January 11, 2024 at 10:05 am #8113janParticipantDear Jijo,
gravity is applied as a (constant) external acceleration, see
accExt
andapply_gravity
inexamples/particles/dkt2d
. So the changes of the fluid density don’t affect the particle.Also, currently the external acceleration is defined for the whole particle system. Updating it within the
ParticleManager
would therefore update it for all particles. In your particular case, I think it would be best to manually apply the gravity at each timestep. For example, you could evaluate the density at the current particle position if an averaged density is sufficient. If you need different forces on the surfaces, then a more sophisticated approach would be necessary.Best regards,
JanJanuary 11, 2024 at 9:12 pm #8117JijoParticipantDear Jan,
Thank you for your reply. I appreciate your constant support and help. The problem I am having is that the fluid itself is not flowing upward due to natural convection and I think such issue is due to the force field.
It seems that the porousparticleBGK dynamics does not contain a force field and I believe that buoyancy forces are coupled using Boussinesq forces by the Guo forcing scheme. What do you think I should do in this case?
Regards,
January 12, 2024 at 2:16 pm #8119janParticipantDear Jijo,
if you solely need a force field for the coupling, then perhaps try
PorousParticleKupershtokhForcedBGKdynamics
and see if that works.Best regards,
JanOctober 6, 2024 at 11:00 am #9327JijoParticipantDear Jan,
Thank you for your response. The
PorousParticleKupershtokhForcedBGKdynamics
scheme works perfectly; however, I am encountering discrepancies with other forcing schemes. Specifically, when applyingPorousParticleGuoForcedBGKdynamics
to the isothermal DKT problem, the particle settling behavior changes significantly compared to the original scheme. Do you have any idea into what might be causing this issue?For reference, I am testing with the DKT2D example code.
I appreciate any guidance you can provide.
Best regards,
Anas- This reply was modified 4 months, 1 week ago by Jijo.
October 22, 2024 at 1:29 pm #9397ChristophParticipantDear Jijo,
the error in results of various forcing schemes was investigated by Trunk et al. with a case of a single settling sphere in https://www.mdpi.com/2079-3197/9/2/11 . In this paper they found an error of 5 to 8% in the cases they studied when using the Guo forcing scheme.
The DKT2d case is more suszeptible to differences in the forcing scheme, as the settling spheres interfere with each other. This likely causes the large discrepancies you found.
Best regards,
Christoph -
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