Individual air bubble entrainment at a planar plunging jet with near-inception flow conditions

At a plunging liquid jet, air bubbles may be entrained if the impact velocity exceeds a critical velocity. New experiments were performed in a two-dimensional plunging jet to observe the flow conditions at inception. Two mechanisms of air entrainment were visualised : air bubble entrainment by elongated air cavity and by foam bubbles. After entrapment/entrainment, the breakage of entrainment air bubbles depends critically upon the initial bubble size