204 research outputs found
Plunging cavities
International audienceWhen a wave breaks, the tip forms a liquid sheet which impinges the base and creates an air cavity which breaks into bubbles. Gomez-Ledesma, Kiger & Duncan (J. Fluid Mech., this issue, vol. 680, 2011, pp. 5-30) have conducted a nice experiment on this problem, enabling them to discuss both the inclination of the jet and the effect of its translation. This work has interesting links with other transient cavities. © 2011 Cambridge University Press
Beating the teapot effect
We investigate the dripping of liquids around solid surfaces in the regime of
inertial flows, a situation commonly encountered with the so-called "teapot
effect". We demonstrate that surface wettability is an unexpected key factor in
controlling flow separation and dripping, the latter being completely
suppressed in the limit of superhydrophobic substrates. This unforeseen
coupling is rationalized in terms of a novel hydro-capillary adhesion
framework, which couples inertial flows to surface wettability effects. This
description of flow separation successfully captures the observed dependence on
the various experimental parameters - wettability, flow velocity, solid surface
edge curvature-. As a further illustration of this coupling, a real-time
control of dripping is demonstrated using electro-wetting for contact angle
actuation.Comment: 4 pages; movies at http://lpmcn.univ-lyon1.fr/~lbocque
A universal law for capillary rise in corners
International audienceWe study the capillary rise of wetting liquids in the corners of different geometries and show that the meniscus rises without limit following the universal law: h(t)/a â (ÉŁt/na)â
, where ÉŁ and n stand for the surface tension and viscosity of the liquid while a =âÎł /ÏÉŁ g is the capillary length, based on the liquid density p and gravity g. This law is universal in the sense that it does not depend on the geometry of the corner. © 2011 Cambridge University Press
A fluid mechanical view on abdominal aortic aneurysms
Abdominal aortic aneurysms are a dilatation of the aorta, localized preferentially above the bifurcation of the iliac arteries, which increases in time. Understanding their localization and growth rate remain two open questions that can have either a biological or a physical origin. In order to identify the respective role of biological and physical processes, we address in this article these questions of the localization and growth using a simplified physical experiment in which water (blood) is pumped periodically (amplitude a, pulsation Ï) in an elastic membrane (aorta) (length L, cross-section A0 and elastic wave speed c0) and study the deformation of this membrane while decharging in a rigid tube (iliac artery; hydraulic loss K). We first show that this pulsed flow either leads to a homogenous deformation or inhomogenous deformation depending on the value of the non-dimensional parameter c02/(aLÏ2K). These different regimes can be related to the aneurysm locations. In the second part, we study the growth of aneurysms and show that they only develop above a critical flow rate which scales as A0c
Explosions at the water surface
International audienceWe study the shape and dynamics of cavities created by the explosion of firecrackers at the surface of a large pool of water. Without confinement, the explosion generates a hemispherical air cavity which grows, reaches a maximum size and collapses in a generic w-shape to form a final central jet. When a rigid open tube confines the firecracker, the explosion produces a cylindrical cavity that expands without ever escaping the free end of the tube. We discuss a potential flow model, which captures most of these feature
Transonic liquid bells
http://www.irphe.univ-mrs.fr/~clanet/PaperFile/PHFBell.pdfThe shape of a liquid bell resulting from the overflow of a viscous liquid out of a circular dish is investigated experimentally and theoretically. The main property of this bell is its ability to sustain the presence of a ââtransonic point,'' where the liquid velocity equals the speed of antisymmetricâor sinuousâsurface waves. Their shape and properties are thus rather different from usual ââhypersonic'' water bells. We first show that the bell shape can be calculated very accurately, starting from the sonic point.We then demonstrate the extreme sensitivity of the shape of these bells to the difference of pressure across the interface, making them a perfect barometer. Finally, we discuss the oscillations of the bell which occur close to the bursting limit
Valveless pumping at low Reynolds numbers
Pumping at low Reynolds number is a ubiquitously encountered feature, both in
biological organisms and engineered devices. Generating net flow requires the
presence of an asymmetry in the system, which traditionally comes from
geometric flow rectifiers. Here, we study a valveless system of oscillating
pumps in series, where the asymmetry comes not from the geometry but from time,
that is the phase shifts between the pumps. Experimental and theoretical
results are in very good agreement. We provide the optimal phase shifts leading
to the maximal net flow in the continuous limit, larger
by 25\% than that of a traditional peristaltic sinusoidal wave. Our results
pave the way for the design of more efficient microfluidic pumps.Comment: 6 pages, 5 figure
Coating of a textured solid
International audienceWe discuss how a solid textured with well-defined micropillars entrains a film when extracted out of a bath of wetting liquid. At low withdrawal velocity V, it is shown experimentally that the film exactly fills the gap between the pillars; its thickness hd is independent of V and corresponds to the pillar height hp. At larger velocity, hd slowly increases with V and tends towards the Landau-Levich-Derjaguin (LLD) thickness h LLD observed on a flat solid. We model the entrainment by adapting the LLD theory to a double layer consisting of liquid trapped inside the texture and covered by a free film. This model allows us to understand quantitatively our different observations and to predict the transition between hp and hLLD. © 2011 Cambridge University Press
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