Local air entrainment and detrainment

Abstract

Air and water are usually well separated by gravity due to their extreme difference in specific weight. Whenever they are mixed, however, they give rise to a very complex two-phase flow situation. The hydraulic engineer is often faced with the problem of estimating the effects of entrained air upon the flow, because this may be essential for the safe operation of a hydraulic structure.The predominant mechanism in generating airwater mixtures is the inclusion of air at the surface of flowing water. The mechanics of free-surface flow may lead to ambient surface aeration in high-speed flows, or - even at moderate flow velocities - to flow configurations with localized air entrainment, which includes inadvertent self-aeration as well as such specific flow systems in which surface aeration is forced.