Abstract: Self-aeration of open channel flows is common in hydraulic engineering. When flow velocity is high, air bubbles are transported up to the channel bottom under violent turbulences, forming fully aerated water flow. At present, most of the previous studies on water flow aeration are based on the physical model tests, which have a significant scale effect. This paper describes a set of numerical models we have developed recently, including a mixing model, a turbulence model, and a concentration model. These numerical models are discretized and solved using a finite difference method. Then, they are verified through comparing the calculations of air concentration and water velocity in open channel flows with previous self-aeration experiments, achieving a good agreement and showing their applicability to the study of hydraulic characteristics of the fully aerated flows. Further examination of the calculation results reveals that in the fully aerated water flow, entrained air can reach the channel bottom due to violent turbulences, and reduce the wall resistance to the flow, thus resulting in a channel flow velocity higher than that of the corresponding non-aerated flow.

Key words: numerical simulation, mixture model, concentration model, air concentration, flow velocity