From Odwiki

[edit] Dynamics : Fluid Simulation

ComputationalFluidDynamics (CFD) (or FluidSimulation) is the simulation of fluids (gasses or liquids). Houdini has no built-in fluid dynamics solvers yet, but it's possible to import the results of a 3rd party solver into Houdini.

ComputationalFluidDynamics is a Dynamics solver.

[edit] Built-in ComputationalFluidDynamics solvers

Houdini 9.0+ has two CFD solvers built in to DOPs:

• ParticleFluidSolver - using what is called SPH : Smoothed Particle Hydrodynamics
• FluidSolver - a solver using a technique known as PLS: Particle Level Set

[edit] 3rd Party ComputationalFluidDynamics solvers

• RealFlow by NextLimit has Houdini import/export support developed my MarkStory at DigitalCinemaArts' RealFlow plugin page : http://www.digitalcinemaarts.com/dev/real_flow/index.html