vertical stacking of fluids of different density

[shapevoid]

Hello,

Im looking for a solution to be able to vertically stack liquids of different density, obviously this is slightly removed from reality as most liquids would just mix, however what I want to do is add layers of different liquids in a tube. Can I exaggerate the properties of the particles to ensure that some liquids (eg milk) will have a greater density than others (eg honey), therefore allowing me to stack them vertically?

Cheers

[josemendez]

Hello,

Im looking for a solution to be able to vertically stack liquids of different density, obviously this is slightly removed from reality as most liquids would just mix, however what I want to do is add layers of different liquids in a tube. Can I exaggerate the properties of the particles to ensure that some liquids (eg milk) will have a greater density than others (eg honey), therefore allowing me to stack them vertically?

Cheers

Hi there!

If your densest fluids are at the bottom and your lightest fluids on top, then stacking is what happens in real life and obi will simulate it nicely

However if you want to stack higher-density fluids on top of lighter fluids... things get complicated.

There's no fail-proof way of stacking dense fluids on top of lighter ones. In real life, the slightest perturbation at the fluid interface produces what is known as the Raleigh-Taylor instability: https://www.youtube.com/watch?v=NI85oC-3mJ0

Simulators are specifically designed to reproduce this phenomenon, and the lack of it is an indicator in the general case that something is seriously wrong with the math.

You could be able to exploit numerical precision issues and low-resolution fluid, together with very low density differences between the fluids to force the instability to disappear, but this is very platform and settings dependent so I wouldn't rely on it.

Edit: in this video, you can see Obi simulating several fluids of different densities. Depending on how big the difference in density is, fluids will take longer to stratify, but towards the end of it you can see the fluids settle in layers.