Dynamics of a drop trapped inside a circular hydraulic jump

We investigate the dynamics of a drop trapped inside a circular hydraulic jump : in our experiment, a circular hydraulic jump is formed by a viscous jet impacting a horizontal glass disk. A drop of the same liquid, deposited in the jump does not coalesce, and remains trapped at its periphery, because of the air entrainment linked to the high drop rotation speed. Depending on the flow rate, the drop can exhibit complex dynamics, from regular rotation along the jump to ``chaotic'' behaviour. We also studied in detail hydrodynamics of the liquid drop and its interaction with the jump. Our investigations show that hydrodynamics of the jump is still not fixed.