Fluid simulation solves the Navier-Stokes equations, the physics of liquids and gases, on a grid each frame: velocities advect, pressure equalizes, vortices curl. Jos Stam’s 1999 stable fluids method made it real-time; GPUs made it high resolution.
How real-time fluids work
The screen becomes a grid of cells, each holding a velocity and whatever the fluid carries (ink density, temperature, color). Every frame the solver makes a few passes. Advection moves quantities along the velocity field. Forces are injected: gravity, a stir, an audio impulse. A pressure solve then nudges the field back toward incompressibility, and that step is where the curling, vortex-shedding character comes from. Stam’s insight was making each step unconditionally stable, so the simulation bends rather than explodes when pushed hard. A modern GPU runs this at high resolution with power to spare, which is why convincing smoke now lives in browser demos.
Where you meet it
Film effects run enormous offline versions for water and fire. Games run coarse ones for smoke. In live visuals the fluid sim is a genre of its own: the swirling-ink look that reads as expensive because everything real moves this way. Ink blooms, smoke shears, stirring leaves eddies that persist and interact, and audiences grant the physics an instant credibility that hand-animated swirls never earn.
Steered, not posed
The cost is control: a simulation cannot be keyframed into a pose, only pushed and coaxed. That trade suits music exactly. Audio input works as forces, a kick as an impulse into the velocity field, sustained bass as a slow stir, and the physics improvises the rest. This is how Photism’s fluid scene runs: real Navier-Stokes, stirred by the music, never the same twice.