Multiple rotations of a drop rolling inside a horizontal circular hydraulic jump

We explore the complex dynamics of a non-coalescing drop of moderate size inside a circular hydraulic jump of the same liquid formed on a horizontal disk. In this situation the drop is moving along the jump and one observes two different motions: a periodic one (it orbits at constant speed) and an irregular one involving reversals of the orbital motion. Modeling the drop as a rigid sphere exchanging friction with liquid across a thin film of air, we rationalize both the orbital motion and the internal rotation of the drop. This internal rotation is evidenced by tracer visualization and exhibits an unexpected dependence upon drop size.