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Effect of surfactants on the inertialess instability of a two-layer film flow

Published online by Cambridge University Press:  30 October 2007

PENG GAO  and
XI-YUN LU
PENG GAO
Affiliation:
Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026, China
XI-YUN LU*
Affiliation:
Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026, China
*
†Author to whom correspondence should be addressed: [email protected]
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Abstract

The effect of insoluble surface and interfacial surfactants on the inertialess instability of a two-fluid film flow down an inclined plane is investigated based on a normal mode analysis. The results reveal that the inertialess instability of relatively long waves can be predominantly weakened by a surface surfactant and enhanced by an interfacial surfactant. For sufficiently large viscosity ratio of the upper layer to the lower one, a destabilizing influence of the surface surfactant is also detected; this is thus a rare example demonstrating the possible destabilizing effect of the surfactant on the flow with a free surface. When the upper layer is less viscous and hence the instability due to the viscosity stratification disappears, a new instability can be triggered by the presence of an interfacial surfactant. Both the surfactants on the surface and the interface can stabilize or destabilize the short-wave instabilities, which occur for negligible surface and interfacial tensions.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 591 , 25 November 2007 , pp. 495 - 507
Copyright
Copyright © Cambridge University Press 2007

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