706 research outputs found
Liquid interfaces in viscous straining flows: Numerical studies of the selective withdrawal transition
This paper presents a numerical analysis of the transition from selective
withdrawal to viscous entrainment. In our model problem, an interface between
two immiscible layers of equal viscosity is deformed by an axisymmetric
withdrawal flow, which is driven by a point sink located some distance above
the interface in the upper layer. We find that steady-state hump solutions,
corresponding to selective withdrawal of liquid from the upper layer, cease to
exist above a threshold withdrawal flux, and that this transition corresponds
to a saddle-node bifurcation for the hump solutions. Numerical results on the
shape evolution of the steady-state interface are compared against previous
experimental measurements. We find good agreement where the data overlap.
However, the numerical results' larger dynamic range allows us to show that the
large increase in the curvature of the hump tip near transition is not
consistent with an approach towards a power-law cusp shape, an interpretation
previously suggested from inspection of the experimental measurements alone.
Instead the large increase in the curvature at the hump tip reflects a
logarithmic coupling between the overall height of the hump and the curvature
at the tip of the hump.Comment: submitted to JF
Viscous Withdrawal of Miscible Liquid Layers
In viscous withdrawal, a converging flow imposed in an upper layer of viscous
liquid entrains liquid from a lower, stably stratified layer. Using the idea
that a thin tendril is entrained by a local straining flow, we propose a
scaling law for the volume flux of liquid entrained from miscible liquid
layers. A long-wavelength model including only local information about the
withdrawal flow is degenerate, with multiple tendril solutions for one
withdrawal condition. Including information about the global geometry of the
withdrawal flow removes the degeneracy while introducing only a logarithmic
dependence on the global flow parameters into the scaling law.Comment: 4 pages, 4 figure
Breakup of Air Bubbles in Water: Memory and Breakdown of Cylindrical Symmetry
Using high-speed video, we have studied air bubbles detaching from an
underwater nozzle. As a bubble distorts, it forms a thin neck which develops a
singular shape as it pinches off. As in other singularities, the minimum neck
radius scales with the time until breakup. However, because the air-water
interfacial tension does not drive breakup, even small initial cylindrical
asymmetries are preserved throughout the collapse. This novel, non-universal
singularity retains a memory of the nozzle shape, size and tilt angle. In the
last stages, the air appears to tear instead of pinch.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figures. Revised for
resubmissio
Still water: dead zones and collimated ejecta from the impact of granular jets
When a dense granular jet hits a target, it forms a large dead zone and
ejects a highly collimated conical sheet with a well-defined opening angle.
Using experiments, simulations, and continuum modeling, we find that this
opening angle is insensitive to the precise target shape and the dissipation
mechanisms in the flow. We show that this surprising insensitivity arises
because dense granular jet impact, though highly dissipative, is nonetheless
controlled by the limit of perfect fluid flow.Comment: 5 pages, 5 figures, submitted to Physical Review Letter
Dense Suspension Splat: Monolayer Spreading and Hole Formation After Impact
We use experiments and minimal numerical models to investigate the rapidly
expanding monolayer formed by the impact of a dense suspension drop against a
smooth solid surface. The expansion creates a lace-like pattern of particle
clusters separated by particle-free regions. Both the expansion and the
development of the spatial inhomogeneity are dominated by particle inertia,
therefore robust and insensitive to details of the surface wetting, capillarity
and viscous drag.Comment: 4 pages (5 with references), and a total of 4 figure
From splashing to bouncing: the influence of viscosity on the impact of suspension droplets on a solid surface
We experimentally investigated the splashing of dense suspension droplets
impacting a solid surface, extending prior work to the regime where the
viscosity of the suspending liquid becomes a significant parameter. The overall
behavior can be described by a combination of two trends. The first one is that
the splashing becomes favored when the kinetic energy of individual particles
at the surface of a droplet overcomes the confinement produced by surface
tension. This is expressed by a particle-based Weber number . The second
is that splashing is suppressed by increasing the viscosity of the solvent.
This is expressed by the Stokes number , which influences the effective
coefficient of restitution of colliding particles. We developed a phase diagram
where the splashing onset is delineated as a function of both and .
A surprising result occurs at very small Stokes number, where not only
splashing is suppressed but also plastic deformation of the droplet. This leads
to a situation where droplets can bounce back after impact, an observation we
are able to reproduce using discrete particle numerical simulations that take
into account viscous interaction between particles and elastic energy
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