Examples of free surface: Changes in density and velocity in gas cell

[Takayuki Tashiro]

I am a beginner who has only been using OpenLB for a few days.

My understanding is that OpenLB’s free-surface tracking method deals solely with the liquid phase.
However, in freeSurface examples such as ‘BreakingDam2d’, the density and velocity of gas cells located at a distance—beyond the reach of the free-surface cells—vary. In ‘fallingDrop2d’, it can be observed that, immediately after the calculation begins, a distribution resembling a pressure wave propagates from around the droplet and is reflected at the mesh boundary.

Are streaming and collisions within the gas cells also calculated? Or does this mean that, whilst they are calculated, there is no interaction with the surface cells?

Many thanks,
Takayuki

[Tikhon Riazantsev]

Dear Takayuki,

Your intuition is correct – gas cells do undergo collision and streaming. They are however not coupled to interface or fluid cells. They are essentially “passive observers”, only used to compute the zero-pressure boundary condition on the interface, without any mass or momentum transfer.

If you would like to learn more, feel free to ask here or refer to our code in:

/src/dynamics/freeSurfacePostProcessor2D.h

All the best,
Tikhon Riazantsev

[Takayuki Tashiro]

Hello Tikhon,

Thank you for your prompt reply.
I shall take a look at freeSurfacePostProcessor2D.h and the other files.

Kind regards,
Takayuki

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