Are fluid simulations for video games different from "actual" fluid simulations? The article just seemed like a discussion about fluid dynamics, but when it says things like "... for games", I always think it's about making something look realistic without actually solving the real equations.
I think that most fluid simulations for games would be pretty far from physically accurate just for the sake of speed.
Doing a full simulation at any sort of resolution would totally kill your framerate, and you've got a lot of other stuff going on as well.
A relevant quote from Dwarf Fortress developer ToadyOne (regarding the fluid system in DF):
"The only thing impressive about it is probably that it runs at all while everything else is going on".
We believe that a better alternative is to use the physics of fluid flows which have been
developed since the time of Euler, Navier and Stokes (from the 1750’s to the 1850’s). These
developments have led to the so-called Navier-Stokes Equations, a precise mathematical
model for most fluid flows occurring in Nature. These equations, however, only admit analytical
solutions in very simple cases. No progress was therefore made until the 1950’s when
researchers started to use computers and develop numerical algorithms to solve the
equations. In general, these algorithms strive for accuracy and are fairly complex and time
consuming. This is because the applications that require these solvers have to be physically
accurate. It is obviously crucial that the stresses and drag on an airplane or a bridge are
calculated precisely.
In computer graphics and in games on the other hand what matters most is that the
simulations both look convincing and are fast. In addition it is important that the solvers aren’t
too complex so that they can be implemented on standard PCs, game consoles or PDAs. In
this paper we present a set of algorithms which meet these requirements. To achieve these
goals we depart from conventional wisdom in computational physics and develop algorithms
custom tailored for creating visual effects. Unlike physically accurate solvers which have strict
bounds on their time steps, our algorithms are stable, and never “blow up.”
