Abstract
The instability of an interface between two immiscible fluids under an externally vertical oscillation is investigated by using a linear perturbation theory. Two incompressible viscous fluid under the action of gravity are assumed to be bounded by the upper and lower solid walls which are oscillated vertically. The neutral stability curves are found in the plane consisting of the angular frequency and the amplitude of the external oscillation. A critical amplitude of the external oscillation, below which any instability does not arise, is found from the neutral stability curve. The effects of the Reynolds number, the thickness ratio and the viscosity ratio on the critical amplitude are examined. The results obtained theoretically are confirmed experimentally by using two liquid layers consisting of a light oil and aqueous glycerine.
