Help Fluid oddities at <= 4 particles

[slimedev]

That sounds like surface tension. It's a force that acts on particles whose neighborhood is not full of other particles. It acts to clump small groups of particles together into groups while attempting to minimize the surface of the fluid. Since the shape that has less surface to volume ratio is a sphere (circle in 2D), the result is radially symmetric droplets.

Setting the fluid's "polarity" parameter to zero should disable this.

That makes sense. I tested Surface Tension 0 and it got rid of the "point collapse" physics and rendering, although each particle still jitters a bit and meanders. Interesting, thanks for the explanation.

Here are some sample "LittleBigFluid" scenes for Obi 6 & 7 (Unity 2021.3) with the basics setup similarly to my project. Movement is by setting solver's externalForces
I apologize because my copy of Obi 6 is bugged outside of working scenes (no particle/particle interaction) so I cannot say if this Obi6_LittleBigFluid.unity shows a bug or not

   

No sticky issues in Obi 7 with 1-4 particles   (but a new visual bug: At 2 particles the fluid mesh is invisible, so I added 2 fake particle sphere meshes)
Back in my Obi 6 project, changing Viscocity from 10 to 1 .... seems not to change much of the jitter or meandering. I think upgrading to Obi 7 is the solution.

P.S. Obi 7 is very nice! The reduction in components is great. Seeing the fluid mesh in the editor is incredible!! And there are some nice new callbacks as well.