The axisymmetric flow of a very viscous fluid toward a central orifice is studied. In a recent paper, a self-similar solution for this problem has been found. The self-similarity is of the second kind and hence the flow remembers its initial condition only through a nondimensional constant which characterizes it. In this work this convergent flow is studied experimentally (using silicone oils) by measuring the front position and the height profile as a function of time. It is verified that the self-similar solution properly describes the flow within a certain interval of the cavity radius, where values are obtained for the similarity exponent 6 in agreement (accounting for experimental errors) with the theoretical value 0.762.... The transition to the self-similar flow is also simulated numerically and numerical values are obtained for the time closure for different initial conditions. These simulations also show the theoretical self-similar flow after the cavity closure, which is very difficult to observe experimentally.

We study the evolution of a long strip of viscous fluid on a horizontal glass substrate under partial-wetting conditions. This initial condition develops into an array of quasi-equidistant drops. The special feature of this dewetting scenario is that the pearling process, consisting of successive stages of bulge growth and pinching-off, does not occur simultaneously along the strip but propagates from the ends toward the strip center. We find that the footprint of each drop corresponds to two crossed elliptical shapes and report measurements of the breakup process and the dewetting dynamics.

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We study the thin-film flow of a constant volume of silicon oil (polydymethilsiloxane) spreading down a vertical glass plate. The initial condition is generated from a horizontal fluid filament of typical diameter 0.4 mm. Two optical diagnostic methods are used: One based on an anamorphic system, and the other on the Schlieren method. The first one allows for a detailed characterization of the early stable stage of the spreading which is used to estimate the thickness of the precursor film needed to model the flow. The second one captures the bidimensional pattern of the transversal film instability. We use these techniques to determine the film thickness profiles, and the evolution of the moving contact line, including its shape and Fourier spectra. The numerical simulations of the stable stage of spreading are in good quantitative agreement with the experimental results. We develop a model based on linear stability theory that predicts the evolution of the modes present in the linear stage of the instability.

This work concerns the spreading of viscous droplets on a smooth rigid horizontal surface, under the condition of complete wetting (spreading parameter S > 0) with the Laplace pressure as the dominant force. Owing to the self-similar character foreseeable for this flow, a self-similar solution is built up by numerical integration from the center of symmetry to the front position to be determined, defined as the point where the free-surface slope becomes zero. Mass and energy conservation are invoked as the only further conditions to determine the flow. The resulting fluid thickness at the front is a small but finite (Z lo-') fraction of the height at the center. By comparison with experimental results the regime is determined in which the spreading can be described by this solution with good accuracy. Moreover, even within this regime, small but systematic deviations from the predictions of the theory were observed, showing the need to add terms modifying the Laplace pressure force.