Swirling against the forcing: Evidence of stable counterdirected sloshing waves in orbital-shaken reservoirs

We report robust experimental evidence of the bistability of sloshing waves in circular cylindrical containers following planar and time-harmonic elliptic orbits. Specifically, we observed for the first time the counterintuitive existence of stable counter-swirling waves. Such novel experimental findings support previous theoretical studies and are here further rationalized by an asymptotic analysis, which shows that this archetypal resonant sloshing system can be well described by 4 degrees-of-freedom only.