Experimental observations of air entrainment and free surface responses from a forced plunging jet*

The quality and reliability of cast metal parts is very sensitive to impurities such as air bubbles and oxide compounds entrained in the melt while pouring the mold. Such impurities can concentrate stresses and shorten the fatigue life of these castings, and therefore there is a great need to understand how these entrainment events occur. While a body of literature on how plunging liquid jets entrain air does exist, there is little understanding yet of how disturbances on these jets cause air entrainment events, with most literature focusing on jets that either lack disturbances entirely or allow them to passively arise from unforced flow noise. This work concerns a novel air entrainment research system that forces harmonic disturbances on a well-controlled jet, enabling exploration of the relationship between a well-defined jet disturbance and air entrainment onset, its destabilization mechanism, and the eventual entrainment rate. Results from those investigations will be presented, including the finding of a novel free surface instability driven by the harmonic jet disturbances.