As a first step towards a full-featured fluid simulator, I am currently working on smoke simulation, and now got something running for the simplest case of smoke in an open volume, i.e., without any solid objects or boundaries. The attached video shows 10 seconds of simulation with a small heat / velocity source at the bottom left. Looks neat already!
The implementation follows the approach laid out in the SIGGRAPH 2007 Course Notes on Fluid Animation. In brief, this is a Semi-Lagrangian advection scheme, running on a 128^3 grid. My current single-threaded CPU implementation is ridiculously slow (about 4 frames / minute on my i7 Laptop), so I am going to investigate parallelization, probably with OpenCL.
Only the ray marching volume shader utilizes the GPU so far.