The air entrainment template in FLOW-3D HYDRO provides an excellent basis for modeling free surface flows with entrained air such as aerated spillways or plunging jets, in general, flows with unlimited air supply. The modeling approach for such cases is centered around three aspects: air entrainment, the fate of air bubbles (modeled as a dispersed phase), and turbulence, which plays key roles both in air generation and in turbulent diffusion of the gas phase. In cases of limited air supply, like siphons or some tunnel structures, interesting bulking dynamics may develop between the air side and water side; these situations require additional modeling sophistication. The goal of this webinar is to explore some of the more advanced options in FLOW-3D HYDRO that will improve accuracy for unlimited air supply cases, and to better understand the modeling methods available in cases of limited air supply conditions. These include modeling using a 2-fluid VOF approach, but we will see that much can be done within the limits of a 1-fluid VOF approach.