  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 both alu- minum reduction
cells and liquid metal batteries to gain new insights into the rotational wave
motion driven by the metal pad roll instability. Different options are
presented to realize stable and measurable multi-layer stratifications. We
introduce a new acoustic measure- ment procedure allowing to reconstruct wave
ampli- tudes also in opaque liquids by tracking ultrasonic pulse echoes
reflected on the interfaces. Measurements of res- onance curves and phase
shifts were conducted for vary- ing interface positions. A strong influence of
the top and bottom walls were observed, considerably reducing wave amplitudes
and eigenfrequencies, when the inter- face 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.
