Liquids and presets

The Hydro Liquid node gives the liquid its density, viscosity and surface tension in real units.

Units

Setting	Meaning
Units: Physical (default)	Real units. The same liquid looks the same at any domain size or substep count.
Units: Solver	The raw solver values, for tuning.

In Physical units:

Setting	Unit	Examples
Viscosity	mPa·s (centipoise)	water 1, olive oil 80, honey 2,000 to 10,000
Surface Tension	mN/m	water 72.8, oils about 32
Density	kg/m³	water 998, olive oil 910, honey 1,420

Surface tension is relative to water. There is no measurable N/m equivalent in this solver. The lighter liquid floats.

The solver splits the viscosity between its smoothed blend and its implicit solve every frame, from a measured calibration. The same value gives the same liquid at any substep count and domain size.

Presets

The Preset menu writes real-world values at about 20 °C:

Water, Sea Water, Milk, Vegetable Oil, Olive Oil, Motor Oil, Maple Syrup, Honey and Molasses.

Choosing a preset writes its values in Physical units. Custom keeps your own values.

The Hydro templates use these presets. The Honey Coil template keeps a tuned thickness of about 30 times real honey, because its 3 mm particles need it to hold the rope.

Solver-unit settings

Setting	Meaning
Viscosity (Smoothed)	The share of the neighbours’ velocity a particle blends in each substep. Thicker as it rises, and with more substeps.
Implicit Viscosity	Extra stable viscosity for thick liquids, in domain lengths² per second. 0 uses the smoothed blend alone.
Cohesion	The strength that holds the liquid together and rounds drops. 0.05 is water.

More than one liquid

Each Phase ID is its own liquid, up to four (Phase IDs 0 to 3).

• A Phase ID takes the Hydro Liquid of its first emitter that has one, then the solver’s Material socket, then the solver’s own fields.
• Where two liquids touch, viscosity and cohesion use the pair’s mean. This is symmetric, so momentum is conserved.
• The Liquid Two-Phase node controls the interface.

Liquid Two-Phase setting	Default	What it does
Interfacial Tension	1	Cohesion between particles of two different liquids, as a share of the pair’s mean tension. 1 holds them together like one liquid. 0 lets them slide apart.
Phase Separation	0	Repulsion that keeps immiscible liquids apart, such as oil and water.
Phase Density Ratio	0.85	Density of the Phase 1 liquid relative to Phase 0. For example 0.85 for olive oil on water.
Color Diffusion	0	Rate of colour blending when streams collide.

Validation reports two different Hydro Liquids on one Phase ID, and Phase IDs above 3. The Hydro Solver shows Viscosity and Surface Tension only when some liquid uses them.

See the Oil & Water template for a working example: a block of amber oil (Phase 1) dropped onto blue water (Phase 0) in a glass tank, using a Liquid Two-Phase node with Phase Separation 1.5 and Phase Density Ratio 0.8.