Physical Review Fluids

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Persistence of local anisotropy of passive scalars in wall-bounded flows

Wed, 01/17/2018 - 10:00

Author(s): Emmanuel Germaine, Laurent Mydlarski, and Luca Cortelezzi

A persistent small-scale anisotropy of turbulent passive scalar fields, which is independent of the scalar field initial conditions, is observed in direct numerical simulations of fully developed channel flow, even after the flow has undergone substantial mixing, and is attributed to the mean velocity gradient.

[Phys. Rev. Fluids 3, 014606] Published Wed Jan 17, 2018

Generalized derivation of the added-mass and circulatory forces for viscous flows

Wed, 01/17/2018 - 10:00

Author(s): Eric Limacher, Chris Morton, and David Wood

The added-mass concept can be validly applied to viscous flows, provided that the circulatory-force expression accounts for image vorticity. The relationship between added mass and image vorticity is explored, and the most appropriate physical interpretation of added mass is discussed.

[Phys. Rev. Fluids 3, 014701] Published Wed Jan 17, 2018

Derivation of Zagarola-Smits scaling in zero-pressure-gradient turbulent boundary layers

Tue, 01/16/2018 - 10:00

Author(s): Tie Wei and Yvan Maciel

The Zagarola-Smits scaling is derived directly from a detailed analysis of the mass and mean momentum balance in the outer region of the zero-pressure-gradient turbulent boundary layer.

[Phys. Rev. Fluids 3, 012601(R)] Published Tue Jan 16, 2018

Einstein viscosity with fluid elasticity

Tue, 01/16/2018 - 10:00

Author(s): Jonas Einarsson, Mengfei Yang, and Eric S. G. Shaqfeh

Adding a small amount of rigid particles to a viscoelastic fluid leads to interesting suspension rheology, because the gradients near the particles induce elastic stresses in the fluid phase. We derive the viscosity of a dilute suspension of spheres by perturbation theory for a weakly elastic fluid.

[Phys. Rev. Fluids 3, 013301] Published Tue Jan 16, 2018

Transition between quasi-two-dimensional and three-dimensional Rayleigh-Bénard convection in a horizontal magnetic field

Tue, 01/16/2018 - 10:00

Author(s): Tobias Vogt, Wataru Ishimi, Takatoshi Yanagisawa, Yuji Tasaka, Ataru Sakuraba, and Sven Eckert

Rayleigh-Bénard convection is studied in a liquid metal exposed to a horizontal magnetic field. Declining field strength at a given Ra number enables the development of diverse flow oscillations, which are attributed to two-dimensional variations of the roll structure and emerging 3D flow effects.

[Phys. Rev. Fluids 3, 013503] Published Tue Jan 16, 2018

Boundary conditions at the gas sectors of superhydrophobic grooves

Tue, 01/16/2018 - 10:00

Author(s): Alexander L. Dubov, Tatiana V. Nizkaya, Evgeny S. Asmolov, and Olga I. Vinogradova

Local slip boundary conditions at the liquid-gas interface of superhydrophobic grooves with beveled edges and nonuniform depth are investigated. We show that local slip at deep grooves is controlled only by width and bevel angle. This could enable tuning and constraints on large slip in gas areas.

[Phys. Rev. Fluids 3, 014002] Published Tue Jan 16, 2018

Influence of strong perturbations on wall-bounded flows

Tue, 01/16/2018 - 10:00

Author(s): O. R. H. Buxton, M. Ewenz Rocher, and E. Rodríguez-López

Spanwise repeating boundary-layer trips are tested to investigate the influence of various geometrical parameters of the constituent obstacles on the nature of the transition region downstream of the trips, where the artificially generated turbulent boundary layer evolves towards a canonical state.

[Phys. Rev. Fluids 3, 014605] Published Tue Jan 16, 2018

Formation of eyes in large-scale cyclonic vortices

Fri, 01/12/2018 - 10:00

Author(s): L. Oruba, P. A. Davidson, and E. Dormy

Large scale cyclonic vortices, such as tropical cyclones in the Earth atmosphere, exhibit an eye in their center. A new mechanism to understand the formation of such eyes is investigated. Contrary to standard explanations, it is shown that a purely hydrodynamic instability can yield an eye.

[Phys. Rev. Fluids 3, 013502] Published Fri Jan 12, 2018

Growth mechanisms of perturbations in boundary layers over a compliant wall

Fri, 01/12/2018 - 10:00

Author(s): M. Malik, Martin Skote, and Roland Bouffanais

Optimal velocity perturbations arising from the interaction of a turbulent flow with a soft compliant wall. The elastic nature of the wall gives rise to several modes of instability having variable growth depending on the characteristics of the fluid flow as well as the wall properties.

[Phys. Rev. Fluids 3, 013903] Published Fri Jan 12, 2018

Nonlinear growth of the converging Richtmyer-Meshkov instability in a conventional shock tube

Fri, 01/12/2018 - 10:00

Author(s): Marc Vandenboomgaerde, Pascal Rouzier, Denis Souffland, Laurent Biamino, Georges Jourdan, Lazhar Houas, and Christian Mariani

The cylindrical Richtmyer-Meshkov (RM) instability is studied in a shock tube. The growth rate of this instability does not saturate in the nonlinear regime as it does in the planar geometry. Numerical and theoretical studies show that a Rayleigh-Taylor instability superimposes on the RM one and that Bell-Plesset effects enhance the growth of the instability.

[Phys. Rev. Fluids 3, 014001] Published Fri Jan 12, 2018

Driving mechanisms and streamwise homogeneity in molecular dynamics simulations of nanochannel flows

Fri, 01/12/2018 - 10:00

Author(s): Vicente Bitrián and Javier Principe

Molecular dynamics simulations of nanochannel flows generally assume streamwise homogeneity applying an external driving force to represent a pressure gradient. A careful evaluation of this hypothesis shows it to be valid only at low pressure differences due to heating and compressibility.

[Phys. Rev. Fluids 3, 014202] Published Fri Jan 12, 2018

Influence of the impact energy on the pattern of blood drip stains

Thu, 01/11/2018 - 10:00

Author(s): F. R. Smith, C. Nicloux, and D. Brutin

The impact velocity affects the maximum spreading diameter of blood droplets. Observations show that it also affects the width of the bulge visible after evaporation on dried blood drip stains. The interpretation of this phenomenon could have a possible forensic application.

[Phys. Rev. Fluids 3, 013601] Published Thu Jan 11, 2018

Trapping and exclusion zones in complex streaming patterns around a large assembly of microfluidic bubbles under ultrasound

Thu, 01/11/2018 - 10:00

Author(s): Thomas Combriat, Flore Mekki-Berrada, Pierre Thibault, and Philippe Marmottant

We experimentally observe streaming patterns around pulsating bubbles. Under flow, closed recirculation zones appear, that we can predict with a dipolar-like description of the acoustic streaming flow field. This can be extended to model the complex patterns around a large group of bubbles.

[Phys. Rev. Fluids 3, 013602] Published Thu Jan 11, 2018

Dynamics of partially thermalized solutions of the Burgers equation

Thu, 01/11/2018 - 10:00

Author(s): Patricio Clark Di Leoni, Pablo D. Mininni, and Marc E. Brachet

An exploration of how finite dimensional systems reach thermodynamical equilibrium shows that in real space, thermalization first occurs in partial subdomains.

[Phys. Rev. Fluids 3, 014603] Published Thu Jan 11, 2018

Settling and collision between small ice crystals in turbulent flows

Thu, 01/11/2018 - 10:00

Author(s): Jennifer Jucha, Aurore Naso, Emmanuel Lévêque, and Alain Pumir

In cold clouds, small crystals of size ∼ 100 μm settling in a turbulent fluid need to aggregate through collisions to form large hail or graupel particles. Using fully resolved direct numerical simulations, the role of the two main physical processes responsible for collisions is clarified, namely, turbulence and the difference in settling velocity due to different crystals orientations.

[Phys. Rev. Fluids 3, 014604] Published Thu Jan 11, 2018

Three-dimensional flow past a fixed or freely vibrating cylinder in the early turbulent regime

Wed, 01/10/2018 - 10:00

Author(s): Simon Gsell, Rémi Bourguet, and Marianna Braza

Organized three-dimensional structures emerge in the turbulent wakes of bluff bodies. Numerical simulations are employed to track these dominant patterns, explore their evolution in the different flow compartments, and quantify their alteration once the body is subjected to flow-induced vibrations.

[Phys. Rev. Fluids 3, 013902] Published Wed Jan 10, 2018

Turbulent jet from a slender annular slot ventilated by a self-induced flow through the open core

Wed, 01/10/2018 - 10:00

Author(s): Shahid A. Padhani, Gary R. Hunt, and Timothy N. Jukes

An experimental investigation of the turbulent jet which issues from a slender open-core annular source reveals that the near-field dilution is enhanced by entrainment of fluid induced through the core. Exploring the streamwise development using particle image velocimetry, the jet is delineated into four distinct regions.

[Phys. Rev. Fluids 3, 014602] Published Wed Jan 10, 2018

Effect of Prandtl number on heat transport enhancement in Rayleigh-Bénard convection under geometrical confinement

Tue, 01/09/2018 - 10:00

Author(s): Kai Leong Chong, Sebastian Wagner, Matthias Kaczorowski, Olga Shishkina, and Ke-Qing Xia

Heat transport enhancement and flow topology of turbulent Rayleigh-Bénard convection under geometrical confinement are studied numerically for over two decades of Prandtl numbers, with Ra fixed at 108.

[Phys. Rev. Fluids 3, 013501] Published Tue Jan 09, 2018

von Kármán swirling flow between a rotating and a stationary smooth disk: Experiment

Tue, 01/09/2018 - 10:00

Author(s): Aryesh Mukherjee and Victor Steinberg

The much studied von Kármán swirling flow in a small ratio vessel reveals a novel flow structure with a tornadolike rotating core flow in the laminar regime. Although the flow pattern is complicated and differs from von Kármán’s prediction, the friction coefficient scales in accordance.

[Phys. Rev. Fluids 3, 014102] Published Tue Jan 09, 2018

Nanoconfined ionic liquids: Disentangling electrostatic and viscous forces

Tue, 01/09/2018 - 10:00

Author(s): Romain Lhermerout and Susan Perkin

A long-range, apparently electrostatic, interaction has recently been found for surface forces across ionic liquids. Here we disentangle equilibrium and viscous contributions, confirming an exponentially decaying static force, and elucidating the slip boundary condition for drainage of ionic liquid.

[Phys. Rev. Fluids 3, 014201] Published Tue Jan 09, 2018