POF Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Nov 2009

Volume 21, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Phys. Fluids 21, 115105 (2009); http://dx.doi.org/10.1063/1.3263703 (8 pages)

W. J. T. Bos, B. Kadoch, K. Schneider, and J.-P. Bertoglio
Enlarge Image | Read More
Return to All Sections
back to top
RSS Feeds
back to top Interfacial Flows

Spray and microjets produced by focusing a laser pulse into a hemispherical drop

S. T. Thoroddsen, K. Takehara, T. G. Etoh, and C.-D. Ohl

Phys. Fluids 21, 112101 (2009); http://dx.doi.org/10.1063/1.3253394 (15 pages) | Cited 8 times

Online Publication Date: 2 November 2009

Full Text: Read Online (HTML) | Download PDF

multimedia

Show Abstract
We use high-speed video imaging to study laser disruption of the free surface of a hemispheric drop. The drop sits on a glass surface and the Nd:YAG (yttrium aluminum garnet) laser pulse propagates through the drop and is focused near the free surface from below. We focus on the evolution of the cylindrical liquid sheet and spray which emerges out of the drop and resembles typical impact crowns. The tip of the sheet emerges at velocities over 1 km/s. The tip of the crown breaks up into fine spray some of which is sucked back into the growing cavity at about 100 m/s. We measure the size of the typical spray droplets to be about 3 μm. We also show the formation of fine microjets, which are produced when the laser is focused inside the drop and the shock front hits small bubbles sitting under the free surface. For water these microjets are 5–50 μm in diameter and exit at 100–250 m/s. For higher viscosity drops, these jets can emerge at over 500 m/s.
Show PACS
47.15.Uv Laminar jets
47.27.wg Turbulent jets
47.55.dp Cavitation and boiling
47.40.Nm Shock wave interactions and shock effects
47.80.Jk Flow visualization and imaging
66.20.-d Viscosity of liquids; diffusive momentum transport

Convective instabilities in liquid layers with free upper surface under the action of an inclined temperature gradient

A. I. Mizev and D. Schwabe

Phys. Fluids 21, 112102 (2009); http://dx.doi.org/10.1063/1.3251755 (12 pages) | Cited 1 time

Online Publication Date: 3 November 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present the results of an experimental study of convective instabilities in a horizontal liquid layer with free upper surface under the action of an inclined temperature gradient, i.e., when horizontal and vertical temperature gradients are applied at the same time. Silicone oil of 10 cSt (Prandtl number Pr = 102) was employed as the test fluid. We investigated the layers with different thicknesses to examine the influence of gravity on the formation of the convective patterns. It is found out that the system behavior appreciably depends on the dynamic Bond number, which shows a relation of buoyancy and thermocapillary forces. In the case of small dynamic Bond numbers, when the influence of buoyancy is minimal, four different flow patterns, according to the combination of the vertical and horizontal Marangoni numbers, have been found: steady parallel flow, Bénard–Marangoni cells, drifting Bénard–Marangoni cells, and longitudinal rolls. At larger dynamic Bond number, when the influence of buoyancy becomes considerable, new convective structures, named by us the “surface longitudinal rolls” and the “surface drifting cells,” appear in addition to the patterns listed above. These instabilities exist only in the surface part of the thermocapillary flow, whereas the return flow remains stable. Under large enough dynamic Bond number these patterns become the dominating ones, forcing out the classical Bénard–Marangoni instability. We give a phenomenological description of the obtained convective patterns and present the stability diagram in the plane of the vertical and the horizontal Marangoni numbers.
Show PACS
47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
47.54.De Experimental aspects
68.03.Cd Surface tension and related phenomena
47.55.pf Marangoni convection
47.55.nb Capillary and thermocapillary flows

Onset of flow separation for the oblique water impact of a wedge

Yuriy A. Semenov and Bum-Sang Yoon

Phys. Fluids 21, 112103 (2009); http://dx.doi.org/10.1063/1.3261805 (11 pages) | Cited 3 times

Online Publication Date: 9 November 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
For the oblique impact of a wedge on a liquid half space, the limiting angles of the entry velocity and the wedge orientation corresponding to flow separation from the wedge vertex during the initial stage of the impact are investigated on the basis of an analytical solution of the problem. The liquid is assumed to be ideal and incompressible; gravity, surface tension, and air cushioning effects are ignored. The flow generated by the impact is two dimensional and potential. The solution is presented in terms of two governing expressions, which are the complex velocity and the derivative of the complex potential defined in a parameter region. These expressions are obtained using generalized integral formulas for solving mixed and uniform boundary-value problems for the first quadrant. They include two unknown functions, which are the velocity magnitude and angle to the free surface determined from the dynamic and kinematic boundary conditions. The obtained system of integral equations is solved by using the method of successive approximations. The effect of the horizontal component of the entry velocity is studied for various wedge orientations. The analysis of the computations revealed configurations of the impact such that the pressure along the whole length of one side of the wedge becomes less than the pressure on the free surface. Although air effects are not included in the analysis, such a pressure distribution provides conditions for the ventilation of the wedge side, which, in the presence of the air, starts from the contact point on the free surface and extends suddenly along the whole length of the wedge side, thus leading to flow separation from the wedge vertex. The theoretical predictions of flow separation and the experimental data on flow separation by Judge et al. [“Initial water impact of a wedge at vertical and oblique angles,” J. Eng. Math. 48, 279 (2004) ] are remarkably close to each other.
Show PACS
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits
68.03.Cd Surface tension and related phenomena
02.60.Nm Integral and integrodifferential equations
02.60.Lj Ordinary and partial differential equations; boundary value problems

Time-resolved proper orthogonal decomposition of liquid jet dynamics

Marco Arienti and Marios C. Soteriou

Phys. Fluids 21, 112104 (2009); http://dx.doi.org/10.1063/1.3263165 (15 pages) | Cited 2 times

Online Publication Date: 13 November 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
New insight into the mechanism of liquid jet in crossflow atomization is provided by an analysis technique based on proper orthogonal decomposition and spectral analysis. Data are provided in the form of high-speed videos of the jet near field from experiments over a broad range of injection conditions. For each condition, proper orthogonal modes (POMs) are generated and ordered by intensity variation relative to the time average. The feasibility of jet dynamics reduction by truncation of the POM series to the first few modes is then examined as a function of crossflow velocity for laminar and turbulent liquid injection. At conditions where the jet breaks up into large chunks of liquid, the superposition of specific orthogonal modes is observed to track long waves traveling along the liquid column. The temporal coefficients of these modes can be described as a bandpass spectrum that shifts toward higher frequencies as the crossflow velocity is increased. The dynamic correlation of these modes is quantified by their cross-power spectrum density. Based on the frequency and wavelength extracted from the videos, the observed traveling waves are linked to the linearly fastest growing wave of Kelvin–Helmholtz instability. The gas boundary layer thickness at the gas-liquid shear layer emerges at the end of this study as the dominant length scale of jet dynamics at moderate Weber numbers.
Show PACS
47.15.Uv Laminar jets
47.20.-k Flow instabilities
47.15.Cb Laminar boundary layers
47.27.nb Boundary layer turbulence
47.55.Ca Gas/liquid flows
47.27.wg Turbulent jets

Numerical simulation of liquid sloshing in a partially filled container with inclusion of compressibility effects

Y. G. Chen and W. G. Price

Phys. Fluids 21, 112105 (2009); http://dx.doi.org/10.1063/1.3264835 (16 pages) | Cited 3 times

Online Publication Date: 19 November 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A numerical scheme of study is developed to model compressible two-fluid flows simulating liquid sloshing in a partially filled tank. For a two-fluid system separated by an interface as in the case of sloshing, not only a Mach-uniform scheme is required but also an effective way to eliminate unphysical numerical oscillations near the interface. By introducing a preconditioner, the governing equations expressed in terms of primitive variables are solved for both fluids (i.e., water, air, gas, etc.) in a unified manner. In order to keep the interface sharp and to eliminate unphysical numerical oscillations in unsteady fluid flows, the nonconservative implicit split coefficient matrix method is modified to construct a flux-difference splitting scheme in the dual-time formulation. The proposed numerical model is evaluated by comparisons between numerical results and measured data for sloshing in an 80% filled rectangular tank excited at resonance frequency. Through similar comparisons, the investigation is further extended by examining sloshing flows excited by forced sway motions in two different rectangular tanks with 20% and 83% filling ratios. These examples demonstrate that the proposed method is suitable to capture induced free surface waves and to evaluate sloshing pressure loads acting on the tank walls and ceiling.
Show PACS
47.55.Ca Gas/liquid flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.40.Dc General subsonic flows
47.35.-i Hydrodynamic waves
47.20.Ma Interfacial instabilities (e.g., Rayleigh-Taylor)
47.11.-j Computational methods in fluid dynamics

Failure of thermocapillary-driven permanent nonwetting droplets

Peter T. Nagy and G. Paul Neitzel

Phys. Fluids 21, 112106 (2009); http://dx.doi.org/10.1063/1.3253998 (8 pages) | Cited 5 times

Online Publication Date: 20 November 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A droplet may be prevented from molecular contact with a solid surface by providing a thin, lubricating film of surrounding fluid between the solid and liquid surfaces. In this study, we exploit thermocapillary convection, caused by a temperature difference maintained between the droplet and the unwetted surface, to provide this lubricating film. This state may be sustained indefinitely (permanent nonwetting) if the load applied to the droplet does not exceed a threshold. Failure of such systems may be categorized as either film or pinning failures, depending on whether the lubrication film is breached, resulting in a molecular contact between the droplet and the solid surface, or the droplet is forced from its support by losing its pinning contact line. In this work, loads that trigger film and pinning failures are quantified, and their mechanisms explained. Results show that larger loads can be sustained for systems with an elevated temperature difference and for droplets of higher viscosity.
Show PACS
47.55.dm Thermocapillary effects
47.55.nb Capillary and thermocapillary flows
47.55.nd Spreading films
47.55.pb Thermal convection
68.15.+e Liquid thin films
66.20.Ej Studies of viscosity and rheological properties of specific liquids
Return to All Sections
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close