The flow and mixing mechanisms caused by the impingement of an immiscible interface with a vertical jet

This paper summarizes a series of experiments to determine the effects of impinging a water and diesel fuel interface with a water jet. Four distinct flow regimes and associated mixing mechanisms were identified as primarily a function of an interface Richardson number, Ri(i) and to a lesser extent the Reynolds number, Re. In flow regime 1, which occurred at Ri(i)> 15, the jet impinged the interface and formed a slight deformation. Flow behaved similarly to a jet impinging a solid boundary and no mixing was observed. Regime 2 occurred at 15 > Ri(i)> 1.1. With decreasing Ri(i), the interfacial deformation became taller and steeper and a flow separation developed at its edge. Mixing resulted from the formation of a fuel lip at the flow separation point. In regime 3, which occurred at Ri(i)< 1.1, the water jet penetrated deeply into the fuel layer causing an unstable deformation that successively collapsed and reformed. Mixing resulted from the impact of the collapsing deformation. Finally, in regime 4, the jet's momentum was sufficient to impact the solid boundary at the top of the fuel layer, creating a cloud of water droplets. (C) 1999 American Institute of Physics. [S1070-6631(99)04408-6].