INTEC   05402
INSTITUTO DE DESARROLLO TECNOLOGICO PARA LA INDUSTRIA QUIMICA
Unidad Ejecutora - UE
artículos
Título:
Instability of a viscous liquid coating on a cylindrical fiber
Autor/es:
ALEJANDRO G. GONZALEZ, JAVIER A. DIEZ, ROBERTO GRATTON, DIEGO CAMPANA, FERNANDO SAITA
Revista:
JOURNAL OF FLUID MECHANICS
Editorial:
CAMBRIDGE UNIV PRESS
Referencias:
Año: 2010 vol. 651 p. 117 - 143
ISSN:
0022-1120
Resumen:
The instability of a liquid layer coating the surface of a thin cylindrical wire is studied
experimentally and numerically with negligible gravity effects. The initial uniform
film is obtained as the residual of a sliding drop, and the thickness measurements
are performed with an anamorphic optical system that compresses the vertical scale
(allowing to observe several wavelengths) and widens the horizontal one (to follow in
detail the evolution of local minima and maxima). Experimental timelines showing
the growth and position of the maxima and minima are compared with linear theory
and fully nonlinear simulations. A primary mode grows in the early stages of the
instability, and its wavelength ë1 is not always in agreement with that corresponding
to the maximum growth rate predicted by the linear theory ëm. In later stages, a
secondary mode appears, whose wavelength is half that of the primary mode. The
behaviour of the secondary mode allows us to classify the experimental results into
two cases, depending on whether it is linearly stable (case I) or unstable (case II). In
case I, the amplitude of the secondary mode remains small compared with that of
the primary one, while in case II both amplitudes may become very similar at the
end. Thus, the distance between the final drops may be quite different from that seen
between initial protuberances. The analysis of the experiments allows us to define
a simple criterion based on the comparison between ë1 and ëm. Contrary to the
predictions of widely used previous quasi-static theories, experiments show that the
relation between maximum and minimum of the primary mode is better approximated
by a kinematic model based on the assumption that primary maxima increase as fast as the minima decrease. Numerical simulations confirm this hypothesis.