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. GONZÁLEZ; JAVIER A. DIEZ; ROBERTO GRATTON; DIEGO M. CAMPANA; FERNANDO A. 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 L1 is not always in agreement with that corresponding to the maximum growth rate predicted by the linear theory Lm.
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 L1 and Lm.
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.