Measurement of Interface Dynamics and Transfer Applied to a Free Surface Shear Instability

Interfacial dynamics and transport are studied experimentally for flow features that are in the sub-millimeter scales. Such features are typically present on many natural and man-made flows and have dramatic effects on the overall flow behavior. Examples of flows influenced by short waves include capillary waves on the ocean surface, initiation of instabilities leading to primary breakup in jets, or interfacial shear in wavy stratified flows. In spite of their common occurrence and importance, there is a dearth of experimental data at these scales, and the relevant physical processes are not well elucidated. Such studies are challenging because of the small time- and length-scales involved, and the difficulties in instrumenting the flow below small disturbances.;Here, long distance, time-resolved, micro-particle image velocimetry and planar laser induced fluorescence are deployed simultaneously on a thick high-speed wall-jet. Just below the surface of the jet, a thin, intense shear layer is injected, leading to several flow regimes, including steep millimeter waves. This geometry is a very repeatable and controlled canonical flow well suited for studying interface dynamics. It also provides optical access from all sides, which facilitates the deployment of the aforementioned diagnostics in the direct vicinity of the surface. In fact, flow field is resolved simultaneously of both side of the interface.;Advanced processing of the time-resolved data enables to extract relevant fluid dynamics quantities. The latter include the first experimental measurement of surface curvature, surface vorticity, and interfacial shear stress at these scales. They allow the identification and explanation of physical processes responsible for surface instabilities and air entrainment. The data also offer new direction to develop mechanistic models of interface shear and transport.