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Flow

simulations/flow·v1.3.0

IN:3 OUT:4

SUMMARY

Flow is a GPU-accelerated 3D fluid solver that simulates gaseous fluids using a 3D texture-based approach. This operator creates smoke, fire, and atmospheric effects by solving the Navier-Stokes equations for incompressible flow on the GPU. The simulation operates in a volumetric grid where velocity and substance density are stored as 3D textures, allowing for real-time interactive fluid dynamics.

The solver supports substance injection from POP point sources, volumetric source inputs, and various forces including buoyancy, gravity, external force fields, and optical flow. You can control fluid behavior through viscosity (thickness), vorticity (swirling motion), pressure iterations (incompressibility accuracy), and dissipation rates for both velocity and substance density. The simulation maintains mass conservation through a pressure projection step and supports collision boundaries and obstacles defined via 3D textures.

Flow optionally generates particle systems that are advected by the fluid velocity field, creating wispy smoke trails or fire ember effects. Particles can spawn from density regions and inherit color from the substance field with customizable lifespans and variance. The simulation outputs velocity, substance density, and temperature as 3D textures suitable for volume rendering or further processing, making it ideal for smoke plumes, fire effects, atmospheric disturbances, and abstract fluid art.

PARAMETERS

PAGEFlow

Reset	Reset	Pulse to clear simulation and reset to initial state.
Time Scale	Timescale	Simulation speed multiplier per frame (higher = faster evolution).
Time Step	Timestep	Read-only display of effective timestep, equal to 1/FPS of TouchDesigner.
[+]Simulation Bounds	Simbounds	Physical size of simulation volume in world units.
Max Axis Resolution	Maxaxisres	Maximum voxel resolution for longest axis (other axes scale proportionally).
[+]Precision	Precision	Texture precision for simulation data.
[+]Simulation Resolution	Resolution	Read-only display of actual grid resolution.
Velocity Dissipation	Veldissipation	Rate at which velocity decays over time (0 = no damping, 1 = instant decay).
Pressure Iterations	Pressureiters	Number of iterations for pressure solve (higher = more accurate incompressibility).
Viscosity	Viscosity	Fluid thickness controlling resistance to flow (0 = inviscid, higher = thicker).
Diffusion Iterations	Diffusioniters	Solver iterations for viscosity diffusion (only active when viscosity > 0).
Vorticity	Vorticity	Vorticity confinement strength to restore rotational motion (creates swirling detail).
Substance Dissipation	Dissipation	Rate at which substance density fades over time (higher = faster fade).
[+]Substance Color Dissipation	Colordissipation	Per-channel dissipation rates for RGB color (allows colored smoke to fade unevenly).

PAGEInputs

Inject	Inject	Enables injection of substance into the simulation.
Injection POP	Injectionpop	Reference to a POP containing points to use as injection points when no first input is connected.
[+]Inject Position	Injectpos	Default injection position when no input POP connected and no P attribute present.
Inject Scale	Injectscale	Scale multiplier for injection area. Uses 'scale' attribute if present in injection POP.
Inject Gain	Injectgain	Amount of substance added per injection point. Uses 'gain' attribute if present in injection POP.
Inject Strength	Injectstrength	Strength of force applied at injection points. Uses 'strength' attribute if present in injection POP.
Inject Temperature	Injecttemp	Temperature value for injected substance. Uses 'temperature' attribute if present in injection POP.
[+]Inject Color	Injectcolor	Color of injected substance. Uses 'Cd' attribute if present in injection POP.
Add Source	Addsource	Enables continuous source emission into simulation.
Substance Gain	Substancegain	Multiplier for substance density from 3D texture source. Enabled when Add Source is on.
Force Strength	Forcestrength	Multiplier for force computed internally from change in density. Enabled when Add Source is on.
Temperature Gain	Temperaturegain	Multiplier for temperature from alpha channel of 3D texture source. Enabled when Add Source is on.

PAGEForces

Apply Buoyancy	Applybuoyancy	Enables temperature-based buoyancy force (hot rises, cold sinks).
Buoyancy Strength	Buoyancystrength	Overall scale for buoyancy force magnitude.
Gas Weight	Gasweight	Density-based downward force (creates heavy smoke effect).
Cooling Rate	Coolingrate	Rate at which temperature decreases over time.
Expansion	Expansion	Volume expansion from heating (creates outward push).
Apply Gravity	Applygravity	Enables uniform gravity force on velocity field.
[+]Gravity	Gravityvector	Gravity direction vector (default: 0, -1, 0).
Gravity Strength	Gravitystrength	Multiplier for gravity force magnitude.
Surface Level	Surfacelevel	Y-position where gravity begins to take effect.
Add External Force	Addexternalforce	Enables custom 3D vector field force from texture.
External Force TOP	Externalforcetop	3D texture containing RGB velocity force vectors.
External Force Strength	Extforcestrength	Multiplier for external force magnitude.
Add Optical Flow Force	Addopticalflowforce	Enables force from 3D optical flow texture.
Optical Flow TOP	Opticalflowtop	3D texture input for optical flow motion vector computation.
Optical Flow Force Strength	Optiflowforcestrength	Multiplier for optical flow force magnitude.

PAGECollisions

Bounds TOP	Boundstop	Optional 3D texture defining custom boundary regions.
Show Bounds	Showbounds	Visualizes boundary regions in output.
Obstacle TOP	Obstacletop	3D texture defining solid obstacle regions (white = solid).
Render Obstacle	Renderobstacle	Includes obstacle visualization in output.
Obstacle Opacity	Obstacleopacity	Opacity multiplier for rendered obstacles.

PAGEAdvect

Advect	Advect	Enables particle system advection by fluid velocity field.
[+]Solver Mode	Solvermode	Switches between Simple and Advect modes.
Target Particles Update POP	Particlesupdatepop	Reference to a POP node downstream in the network.
Advection Step Scale	Advectionstep	Multiplier for particle advection speed.
Spawn From Density	Spawn	Spawns particles in regions with substance density above threshold.
Number Of Particles	Numparticles	Maximum particles spawned.
Density Resolution Scale (Fraction)	Densityscale	Fraction of simulation resolution used for the density field when spawning particles (lower = faster, less precise).
Density Threshold	Threshold	Minimum substance density required for particle spawning.
Seed	Seed	Random seed for particle spawn positions.
Max Attempts	Maxattempts	Maximum spawn attempts per frame before giving up.
Enable Particle Life	Enableparticlelife	Enables finite particle lifespans with automatic death.
Life Span	Lifespan	Base lifespan in seconds before particle dies.
Life Variance	Lifevariance	Random variation added to base lifespan.

Seed

Lifeseed

Random seed for lifespan variance.

PAGEAdvect

Lookup Substance Color	Lookupcolor	Particles inherit color from substance field at spawn position.
[+]Channel Mask (RGBA)	Channelmask	Selects which RGBA channels are sampled when looking up substance color.
[+]From Low	Fromlow	Input range minimum for color remapping (RGBA).
[+]From High	Fromhigh	Input range maximum for color remapping (RGBA).
[+]To Low	Tolow	Output range minimum for color remapping (RGBA).
[+]To High	Tohigh	Output range maximum for color remapping (RGBA).
Match Bounds To T3D	Matchtot3d	Matches particle advection bounds to the 3D texture input dimensions.

PAGECommon

Free Extra GPU Memory

Freeextragpumem

Free memory that has accumulated when output memory has grown and shrunk.

INPUTS

Input 0 POP – Injection

Input 1 TOP – Source

Input 2 POP – Particles In

OUTPUTS

Output 0 TOP – Substance

Output 1 TOP – Velocity

Output 2 TOP – Temperature

Output 3 POP – Particles Out