Source-driven vibration of a semi-rigid cantilever: Soap film experiments comparing incidence angles α = 0° and α = 180°

Multiscale sample entropy analysis has been developed to quantify the complexity and the predictability of a time series, originally developed for physiological time series. In this study, the analysis was applied to the turbulence data. We measured time series data for the velocity fluctuation, in either the longitudinal or transverse direction, of turbulent soap film flows at various locations. The research was to assess the feasibility of using the entropy analysis to qualitatively characterize turbulence, without using any conventional energetic analysis of turbulence. The study showed that the application of the entropy analysis to the turbulence data is promising. From the analysis, we successfully captured two important features of the turbulent soap films. It is indicated that the turbulence is anisotropic from the directional disparity. In addition, we observed that the most unpredictable time scale increases with the downstream distance, which is an indication of the decaying turbulence.

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Probing soap-film friction with two-phase foam flow

Philosophical Magazine Letters ◽

10.1080/09500830802322160 ◽

2008 ◽

Vol 88 (9-10) ◽

pp. 679-691 ◽

Cited By ~ 1

Author(s):

Ariel I. Balter ◽

James A. Glazier ◽

Rebecca Perry

Keyword(s):

Soap Film ◽

Two Phase ◽

Foam Flow

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Instability of a gravity current within a soap film

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.395 ◽

2014 ◽

Vol 753 ◽

Cited By ~ 2

Author(s):

Raymond E. Goldstein ◽

Herbert E. Huppert ◽

H. Keith Moffatt ◽

Adriana I. Pesci

Keyword(s):

Fluid Flow ◽

Gravity Current ◽

Leading Edge ◽

Soap Film ◽

Plateau Border ◽

Dynamic Variations ◽

Characteristic Wavelength ◽

Overall Stability ◽

Stability Regime ◽

Good Agreement

AbstractOne of the simplest geometries in which to study fluid flow between two soap films connected by a Plateau border is provided by a catenoid with a secondary film at its narrowest point. Dynamic variations in the spacing between the two rings supporting the catenoid lead to fluid flow between the primary and secondary films. When the rings are moved apart, while keeping their spacing within the overall stability regime of the films, after a rapid thickening of the secondary film the excess fluid in it starts to drain into the sloped primary film through the Plateau border at which they meet. This influx of fluid is accommodated by a local thickening of the primary film. Experiments described here show that after this drainage begins the leading edge of the gravity current becomes linearly unstable to a finite-wavelength fingering instability. A theoretical model based on lubrication theory is used to explain the mechanism of this instability. The predicted characteristic wavelength of the instability is shown to be in good agreement with experimental results. Since the gravity current advances into a film of finite, albeit microscopic, thickness this situation is one in which the regularization often invoked to address singularities at the nose of a thin film is physically justified.

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