Fluid crawling up a slanted collider (v6.5.4)

[josemendez]

We have a really weird problem with fluid crawling up the side of a slanted collider. Everything works well as long as the sides of our containers are upright, but as soon as they are slanted, this happens:

Hi,

This is a consequence of fluid being discretized as particles, instead of being a continuous material. All particle based fluid simulators are affected.

Particles are supported by the slanted wall, and the column of fluid is unable to fall back into the main body of fluid because each particle sits on all particles below it due to pressure constraints. The column may even continuously go up if pressure is high enough at the bottom of the container.

Increasing the fluid's surface tension can help prevent this, since fluid particles will stick to each other forming round droplets which prevents columns from emerging.

An even weirder detail is that if I deactivate and reactivate the whole thing (Rigidbody, Collider, Emitter and all) via the Unity editor while it's still running, it starts to crawl up on the right side instead:

Which side it happens is entirely random, because Obi (like most physics engines) is not deterministic: running the same simulation multiple times will not yield the exact same results every time.