I presented some Flip and Point Advection stuff at the March 2014 Vancouver Houdini User Group. The files are here for anybody who was there or anybody interested:
VHUG file (200 something megs. This has the hip file and also the quicktimes and one frame of geo from the rest field setup)
I have two hip files. One is a vorticity solver and rest field setup for flip. The vorticity fades out over time, and the rest fields (which is done post flip sim) can add tons of extra detail at rendertime. Some fun stuff to try: you can also use vorticty to drive density or viscosity and create some neat bubbles or foam or even ‘oobleck’ where the fluid can become more viscous as it becomes more stressed.
The second is a setup that uses Gas Advect to advect points along with a high velocity pyro sim. The pop advect by volumes doesn’t work well with high velocities at your source, so I am using a gas advect node instead. There are a few issues I didn’t quite work out with this setup in houdini 13 (needed more than one substep to get it accurate), but I think it’s working pretty well regardless. Prior to 13 I would merge points, create my ids, etc… essentially creating myown particle system. I do also have another few tricks in this file — such as getting a normal on the points from the gradient of the density field, and then I also take the points and use their colors to color the pyro as well. The examples aren’t the greatest artistically, but should get the point across (and I realize I should have made the terrain darker in the viewport). I’ve used setups like this in production and both have proved extremely useful. And as a last note, the files aren’t perfect, I did them rather quickly in my spare time, so there are likely some mistakes in them or things that can be improved. 🙂