Multi-Phase Fluid Flow

CS 493 Lecture, Dr. Lawlor

So far, we're using three color channels in our fluid simulations:

Red (x) gives our fluid X velocity.
Green (y) gives our fluid Y velocity.
Blue (z) gives the current convergence at this pixel.

We can do interesting things with the fourth channel, alpha. You don't even need any physics, just our backward-looking advection, and you can suddenly see the swirling patterns much more clearly:
Alpha Channel Advection Demo

It's pretty, but it does blur out quite rapidly. This "numerical dissipation" is caused by the repeated averaging effect of the graphics card's bilinear filtering on the texture reads--a higher order filter like bicubic sampling would give less resampling error, if we were willing to implement it.

Generally, you can do lots of interesting things with multiphase flow:

Add a "temperature" phase, and add a bouyancy force to drive convection (try "C.y+=C.a*0.001;" above).
Add a "propane" phase, and you could add physics to simulate combustion.
Add a "smoke" phase, and you could simulate a smoky explosion.

As a grad student, I helped build a solid rocket simulator, where simulation cells on the interior of the solid rocket's core burning zone kept track of XYZ velocity (via momentum), density, energy (temperature), and suspended fuel (aluminum and oxidizer). Fluid simulations of the Earth's molten core include magnetic terms, radioactive heating, and convection to the freezing surface!