A laboratory experiment on the surface and internal waves in two-layered fluids

A laboratory experiment is performed to investigate the generation of periodic waves with small amplitudes in a system of two fluid layers in the presence of the top free surface. A horizontal cylindrical wavemaker with a circular cross section is oscillated in two immiscible fluids, silicon oil and water, and the motions of the free surface and the interface between the two fluids are monitored using laser images, and these results are further confirmed with wave probe measurements. There are two different wave modes depending on the relative phase between the motions of the free surface and the interface; barotropic if they are in phase and baroclinic if they are 180° out of phase. To determine the mode of dominance, the position of the wavemaker (at the free surface, at the interface, and below the interface) and the oscillation frequency are varied and the observed wave profiles are decomposed into barotropic and baroclinic waves. In the high frequency range, irrespective of the wavemaker position, it is observed that barotropic waves are dominant, whereas in the low frequency range, baroclinic waves become more important as the submergence depth of the wavemaker increases.