I ran across these simulations when I was searching for something to do for lab 5 and I thought they were really cool.
There are two simulations. The first simulation has to do with fire and how it burns. You can build a wooden structure and light it on fire to see how it burns. You can also add wind or stone to see how they effect the burning process. The second simulation has to do with water and oil. You can also add wind and foam to this simulation to see how it effects the motion of the mater and how the oil and water mix. I think both of these simulations were done in processing. I thought they were interesting because they show a cool graphic simulation of elements mixing with each other and how they affect each others movements.

Fire Simulation:
http://www.escapemotions.com/experiments/fluid_fire_3/

Water Simulation:
http://www.escapemotions.com/experiments/fluid_water_2/index.html

There are also other cool applets like flame painter and fluid painter.
http://www.escapemotions.com/experiments/flame/index.html#top
http://www.escapemotions.com/experiments/fluid_painter/index.html