Visualization of transient interfacial waves induced by spin-up of two immiscible fluid layers

Abstract

Interfacial waves of two immiscible layers in a spin-up container were investigated using experimental visualization. While the interface near the central part rose up, instability waves propagated in an azimuthal direction on the interface. These waves were mainly caused by Kelvin-Helmholtz instability for the velocity difference between two layers during spin-up, but had complicated transient characteristics owing to the rotation in a closed system. We visualized the structure of the interfacial waves by the use of three types of optical characteristics of the interface. Image processing provided the detailed factors of the interfacial waves that were classified in four life stages from their generation to disappearance. The initial generation process involved many frequency modes due to a large velocity difference, and then a low mode stood out during the growth, and disappeared with an ellipsoidal sloshing mode to achieve the rigid rotation in both layers.

Two-fluid confined flow in a cylinder driven by a rotating end wall

“…The interfacial flow is strongly influenced by centrifugal acceleration, and the interfacial flow alters the ambient flows. This two-way interaction appears stronger for small density differences and large viscosity differences between the two fluids [46]. What is still lacking is a nonlinear numerical investigation of two immiscible fluids with strong sustained shear across the interface.…”

Experimental and Numerical Study of Stratified Sloshing in a Tank under Horizontal Excitation

“…A major feature of the density-stratified liquids sloshing is the presence of interfacial wave due to the density difference, which has seldom been studied [17][18][19]. Chang et al [20] studied the internal interfacial waves between two layers of liquids with different densities in a cylindrical container under vertical periodic excitation and found that the internal interfacial wave mode becomes more and more complicated as the density ratio of the upper and lower liquid layers increases.…”