[František Prinz]

Hi Julius,

thank you for your report from the Young-Laplace test.

Does it mean, in the second post, that you didn’t use the Maxwell construction rule? Are the results the same?
I suppose you do not have any significant variation in density far away from the droplet spatial and time dependent.

First I will try to produce the test maybe for the multiphase single component case if I get the convergence here. Maybe are in the multicomponent flow some discrepancies which lead to a bit different procedure maybe.

For the multicomponent case I do not get any convergence for the pressure/density, even I run the simulation for a long time.

Thanks
Frank

[František Prinz]

Hi Julius,

thank you for the reply, I think I get the unit conversion for this problem. But there appear another questions if I could ask you for help.

1.) I ran the Young-Laplace test to messure the pressure and get the surface tension. In my simulation however varies the calculated pressure far away about 200 l.u. from the droplet of radius 12 l.u. from 0.359973 to 0.359982 on a line of 50 l.u. at 10000 time steps. Could you get if this is a normal state or am I doing something wrong? I mean that the calculated surface tension would have than a high deviation and is depending on the exact position which you use outside the bubble.

2.) Do you know how to implement the MRT operator into the ShanChen model? I tried to find something like ShanChenMRTdescriptor but there isn’t anything in the doxygen and use the standard ForcedMRTdescriptor is not working too.

3.) Are open boundary conditions like velocity inlet or pressure outlet implemented for the ShanChen model? I have not found anything in doxygen.

I am really grateful to you for every answer which helps me moving forward.

Regards
Frank

[František Prinz]

Hi Mathias,

I would like to implement it to openLB but I am not familiar enough with the openLB library. Could anybody from your community be helpful for me if possible?

As a starting point could you refer to any articles where the free surface model is explained?

Thanks
Frank

[František Prinz]

Hi Julius,

thank you for your reply, it helped me to relise the differences between multiphase and multicomponent flow. But I stuck in problem with the non-dimensionalisation. I wanted to perform the Young-Laplace test to evaluate the surface tensions but I don’t know how to get the dimensioned number because in that case there is no velocity. The conversion factor I used are density and viscosity which is hidden in the omega. But there are three SI unit: kg, m and s. When I now can use various radia for the droplet and I get different gammas. For one radius I get the gamma about 70 N/m which is about 1000 times higher than for typical fluids. Do you know, what to change to get the gamma in the right order or if there are any mistakes in my thoughts?
One more problem I fall into are the omegas in the multicomponent flows for both lattices. In the example rayleighTaylor2d are the omegas the same for both lattices, but what to do, if the kinematic viscosities for both fluids are different? Can I use different values for both? I tried some numbers out but the simulation was unstable.
The implemenatation of the Li’s force etc. I also want to do but first I must understood the fundamentals of the model.

Thanks
Frank

[František Prinz]

One more extension I would like to implement is a centrifugal force in radial coordinates. For examples a cylinder rotating arround the symmetry axis. In this case the force is no more linear and I think it is not possible to use the AnayliticalLinear2D functor. How can I define arbitrary forces of more complicated form (e.g. depending on the radial distance…)?

Thanks
Frank

[František Prinz]

Yes, this was the problem, thank you Mathias.

[František Prinz]

Hey Marc,

thank you for the reply. The error was really in the lattice coordinates instead of physical coordinates, it is a little bit unintuitive to set lattice velocity and physical coordinates if one doesn’t know it.

Best
Frank

[František Prinz]

Hi Nicolas,

thank you very much, I thought that distance2Wall is the Radius of the channel, but it is the difference to the nearest node.

Regards,
Frank

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