Measurement of interfacial wave dynamics in orbitally shaken cylindrical containers using ultrasound pulse-echo techniques

 We present a novel experiment on interfacial wave dynamics in orbitally shaken cylindrical vessels containing two and three fluid layers. The experiment was designed as a hydrodynamical model for liquid metal batteries. It is intended to shed new light into some aspects of the very similar rotational wave motion emerging due to the metal pad roll instability, as the viscous damping behavior or the contact line dynamics. Both issues can be important to better predict instability onsets for upcoming liquid metal batteries and lab-size experiments. Different options are presented to realize stable and measurable multi-layer stratifications. We introduce a new acoustic measurement procedure allowing to reconstruct wave amplitudes also in opaque liquids by tracking ultrasonic pulse echoes reflected at the interfaces. Measurements of resonance curves and phase shifts were conducted for varying interface positions. A strong influence of the top and bottom walls was observed, considerably reducing wave amplitudes and eigenfrequencies, when the interface is getting close. Finally, measured resonance curves were successfully compared with an existing forced wave theory that we extended to two-layer interfacial waves. The comparison stresses the importance to carefully control the boundary condition at the contact line.