When water moves rapidly, it always entrains air and generates air bubbles and foam. As foam has fluid-like properties, this can be modeled as a change of state, and the simulation becomes a 2-fluid sim, which RealFlow handles very well.

The main breakthrough on this front was to determine the optimal conditions for changing state in a stable way, but our methods include post-processing type foam generation which produce nearly as dynamic effects but much faster than the full dynamic calculation.

[ Foamy flow perspective, front view ]

[ Foamy flow, side view]

[ Foamy flow perspective, rear view]