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• #5692
Gloriousface
Participant

Hello，all

I am trying to simulate the flow of oil droplets in water by SC multi-component model. The oil drops are in the middle of the channel. I try to set the velocity and pressure boundary at the inlet and outlet of the Latticeone（water）, but the Latticetwo（oil） does not set the boundary. The simulation is divergent. May I ask if I need to set the boundary for the oil droplets, or adopt other methods, if someone can help me solve this problem, I would be grateful.

Best，
Gloriousface

#5696
stephan
Moderator

Dear Participant,

yes, you should set boundaries for all lattices.
It might help to have a look at another multicomponent simulation (though with the Free Energy Model) where various boundary conditions are set (/examples/multiComponent/microFluidics2d/).

Best,
Stephan

#5697
Gloriousface
Participant

Dear stephan，

Thank you very much for your reply. After reading microFluidics2d, I tried to set the inlet speed and outlet pressure boundary for latticeone (water) and latticetwo (oil) respectively, but the program is still divergent. Do I need to set the speed for the oil drop itself? The flow of oil droplets in the water has been bothering me for a long time. I can’t successfully set the boundary and don’t know where the problem is. I hope you can help me solve this problem and I would like to express my sincere thanks.

#5698
stephan
Moderator

Dear Participant,

to ensure that the flow problem is well-posed please have a look at the standard literature (see Krüger et al. 2017 “The lattice Boltzmann method” or Huang et al. 2015 “Multiphase Lattice Boltzmann Methods: Theory and Application” and references therein).
Also, please start with “ideal” parameter settings (e.g. low Reynolds number) to prevent numerical instability (see e.g. Krüger et al., Chapter 9).

As such this is currently all I can do, since it is hard to tell where the issues are without going into detail.

BR
Stephan

#5699
Gloriousface
Participant

Dear stephan，

Thank you for your reply in your busy schedule. I plan to read these two books first to understand the connotation of boundary conditions.

Best
Gloriousface

#5717
Gloriousface
Participant

Hello，all

I’m simulating the flow of oil and water. It’s difficult to set the density of the two components. The following is the density of the two components I set, but the simulation results beat very seriously. Is there any problem with this setting？

AnalyticalConst2D<T,T> waterrho( 1 );
AnalyticalConst2D<T,T> oilrho( 0.8 );

#5721
stephan
Moderator

It is hard to tell what exactly triggers the divergence.
The two lines of code you included simply refer to (as the name tells) analytical constants set in your program.
Dependent on what for (and also how) you use them, instability occurs.

#5725
Gloriousface
Participant