October 30, 2020 at 2:37 pm #5259JuliusParticipant
I am currently using the ShanChen single component multiphase flow in combination with a bounce back wall. The wall has an artifical density to incorporate wettability. I run into instability issues during the first few steps when the fluid just beyond the wall is too far off from the wall density. I.e. a more hydrophilic wall starting off with vapour adjacency. The instablity can be avoided by increasing the vapour density, but that results in droplets forming elsewhere which gives not very accurate initial conditions.
My first thought was to ramp up the density of the wall to avoid this huge denstiy gradient, but looking at the BounceBack class, once a fake density is set, it cannot be changed. (maybe add such a possibility in future OpenLB release? )
My other thought is to set the fluid density next to the wall to the wall density during the prepareLattice step. I saw the
indicatorF2D.hwhich makes it seem possible to generate an indicator for the fluid nodes next to the walls.
Using this indicator in the
iniEquilibriumfunctions directly does not work since they require a
SuperIndicatorF2D. Is it possible to get a
SuperIndicatorF2Dfrom a normal
As an alternative, I had hoped on using this indicator to create an
AnalyticalIdentitymuch like the
SmoothIndicatorCircle2D, but it seems that the
SmoothIndicatorCircle2Dis derived from
IndicatorF2D, which makes it incompatible.
One other method I tried was using the IndicatorLayer to set the fluid right next to the wall to a different material. Then with this material get the
IndicatorLayer2Dconstructor requires a
IndicatorF2D, but I’m unsure how to get an indicator of the wall itself with
IndicatorF2Das a base class. The
SuperIndicatorF2Dwhich is derived from
So my question is: How do I use IndicatorLayer2D to set the density the fluid adjacent to the wall to the density of the wall?
Julius WeinmillerOctober 30, 2020 at 8:12 pm #5260mathiasKeymaster
the idea with the ramp may work. You may implement a set function to change the density at a bounce back node. I would go for that idea. The other one you can use the rename functions from superGeometry to introduce a layer with a new material, lets say 43:
– rename(1,42,1,1,1) renames the inner 1 to 42
– rename(1,43) renaes the remainding layer with material 1 to 43
– rename(42,1) renames the inner 42 back to 1
MathiasNovember 2, 2020 at 11:51 am #5262JuliusParticipant
Thank you for the rename trick.
I have managed to get my simulations to work with the ramp idea, but the possiblity to set layers is helpful and opens up some other simualtion possibilities.
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