Controlling the shape of the interfacial boundary is an important technological task. The effect of rotation velocity modulation on the interface between light viscous and denser low viscosity fluid in a rotating horizontal cylinder is studied experimentally. Liquids are characterized by a high contrast of viscosities, these are glycerin and a low-viscosity (denser) fluorinert FC-40. Glycerin is stained with rhodamine, which makes it possible to study the shape of the interface by photo registration with high accuracy when illuminating liquids with a green laser, which causes rhodamine fluorescence. Experiments are carried out in the centrifuged state of liquids when the gravity field has no effect while varying the rotation speed, as well as the amplitude and frequency of librations. It is found that librations qualitatively change the shape of the interface near the ends of the cavity without affecting the cylindrical interface in the middle cavity part. It is shown that this is due to different "viscous" interactions of liquids with the ends of the oscillating cavity, as a result of which the interface near the ends performs radial oscillations with a frequency of librations, and the latter leads to an averaged radial displacement of the wetting boundary of the ends, which increases with the modulation amplitude. At certain amplitudes, the contact line reaches the outer boundary of the cavity. It is shown that the dynamic equilibrium of the interface between liquids of different densities is determined by the averaged interaction of liquids of different viscosity with the oscillating ends.
The dynamics of a phase inclusion in a coaxial liquid layer divided with a radial partition is studied experimentally. The working volume of the container is filled with a viscous liquid, inside which an air bubble, immiscible with the main phase, is injected. This inclusion has a lower density than the surrounding liquid does. The container performs rotational oscillations as a whole with the zero average rotation. Such a motion brings to the generation of a harmonically oscillating azimuthal shear flow, which, as a consequence, excites the oscillations of the phase inclusion. During the bubble’s oscillations, the displacement of its geometric center follows the sinusoidal law. On the background of such a motion a periodic deformation of the bubble is observed, i.e. the phase boundary starts oscillating. A new and surprising result of the experiments is found, when the light bubble sinks and takes a quasi-steady position near the inner wall of the layer.
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