Physical Review Fluids

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Inertia-driven jetting regimes in microfluidic coflows

Mon, 09/17/2018 - 11:00

Author(s): Fan Zhang, Arnaud Erriguible, Théo Gavoille, Michaël T. Timko, and Samuel Marre

Inertial breakup modes are identified at microscale for co-flowing jets using a high-pressure mixer.

[Phys. Rev. Fluids 3, 092201(R)] Published Mon Sep 17, 2018

Normal shocks with high upstream pressure

Mon, 09/17/2018 - 11:00

Author(s): William A. Sirignano

A normal compressive shock with upstream pressure from 10 to 500 bar is analyzed for density, enthalpy, entropy, and velocity with nitrogen, oxygen, argon, and carbon dioxide. New descriptions for sound speed, Prandtl’s relation, the Rankine-Hugoniot relation, and Riemann invariants are presented.

[Phys. Rev. Fluids 3, 093401] Published Mon Sep 17, 2018

Rayleigh-Taylor turbulence with singular nonuniform initial conditions

Wed, 09/12/2018 - 11:00

Author(s): L. Biferale, G. Boffetta, A. A. Mailybaev, and A. Scagliarini

Three-dimensional direct numerical simulations of Rayleigh-Taylor turbulence with various initial unstable temperature distributions finds a modified self-similar mixing in the long term.

[Phys. Rev. Fluids 3, 092601(R)] Published Wed Sep 12, 2018

Collisions of drops with an immiscible liquid jet

Wed, 09/12/2018 - 11:00

Author(s): Carole Planchette, Sylvain Petit, Hannes Hinterbichler, and Günter Brenn

The collisions of a drop stream with an immiscible jet are experimentally studied revealing the formation of several complex structures classified in four main regimes. When neither the drops nor the jet fragment,“drops in jet” are observed that could be hardened to produce advanced fibers.

[Phys. Rev. Fluids 3, 093603] Published Wed Sep 12, 2018

Thermophoresis of Janus particles at large Knudsen numbers

Wed, 09/12/2018 - 11:00

Author(s): Tobias Baier, Sudarshan Tiwari, Samir Shrestha, Axel Klar, and Steffen Hardt

At large Knudsen numbers a Janus particle in a thermal gradient shows a preferred orientation. The interplay between rotational diffusion and thermophoretic motion is investigated.

[Phys. Rev. Fluids 3, 094202] Published Wed Sep 12, 2018

Shear-induced migration and orientation of rigid fibers in an oscillatory pipe flow

Mon, 09/10/2018 - 11:00

Author(s): Scott Strednak, Saif Shaikh, Jason E. Butler, and Élisabeth Guazzelli

Fibers in suspension migrate towards the center of the pipe where they are more aligned with the flow. The migration depends on the fraction of the volume of the suspension swept out by the rotating fibers.

[Phys. Rev. Fluids 3, 091301(R)] Published Mon Sep 10, 2018

Forced wakes far from threshold: Stuart-Landau equation applied to experimental data

Mon, 09/10/2018 - 11:00

Author(s): S. Boury, B. Thiria, R. Godoy-Diana, G. Artana, J. E. Wesfreid, and J. D'Adamo

The Stuart-Landau reduced order model is tested with experimental data from the wake of a cylinder wake forced by plasma actuators, finding an important role played by the changing mean flow.

[Phys. Rev. Fluids 3, 091901(R)] Published Mon Sep 10, 2018

Entrainment model for fully-developed wind farms: Effects of atmospheric stability and an ideal limit for wind farm performance

Mon, 09/10/2018 - 11:00

Author(s): Paolo Luzzatto-Fegiz and Colm-cille P. Caulfield

A new model of wind farm aerodynamics establishes an upper bound for power density, which is an order of magnitude larger than achieved by contemporary turbine arrays. The model also provides a one-equation prediction for the output of existing wind farms, and can include atmospheric stability.

[Phys. Rev. Fluids 3, 093802] Published Mon Sep 10, 2018

Asymmetric concentration dependence of segregation fluxes in granular flows

Mon, 09/10/2018 - 11:00

Author(s): Ryan P. Jones, Austin B. Isner, Hongyi Xiao, Julio M. Ottino, Paul B. Umbanhowar, and Richard M. Lueptow

Particles differing in size or density segregate in dense granular flows. In bidisperse mixtures, the sinking (small or heavy) species concentration that maximizes the segregation flux is <50% and decreases with increasing size or density ratio, matching a classic kinetic-sieving model.

[Phys. Rev. Fluids 3, 094304] Published Mon Sep 10, 2018

Extremes, intermittency, and time directionality of atmospheric turbulence at the crossover from production to inertial scales

Mon, 09/10/2018 - 11:00

Author(s): E. Zorzetto, A. D. Bragg, and G. Katul

A study of how the interplay between mechanical and buoyant production of turbulent kinetic energy affects fully developed atmospheric turbulent flows finds impacts both on the frequency of extreme scalar fluctuations and on the time-directional properties of scalar Eulerian measurements.

[Phys. Rev. Fluids 3, 094604] Published Mon Sep 10, 2018

Fluidity, anisotropy, and velocity correlations in frictionless, collisional grain flows

Fri, 09/07/2018 - 11:00

Author(s): Diego Berzi and James T. Jenkins

We propose corrections to the kinetic theory for fluidity in granular flows near random close packing, in order to take account of anisotropy and increases in granular temperature.

[Phys. Rev. Fluids 3, 094303] Published Fri Sep 07, 2018

Statistics of incremental averages of passive scalar fluctuations

Fri, 09/07/2018 - 11:00

Author(s): Colin R. Meyer, Laurent Mydlarski, and Luminita Danaila

An investigation of the statistics of incremental averages of passive scalar fluctuations shows that, unlike statistics of their differences, they inherit information from the scalar field’s large scales, for averages over all increment sizes, and can differ from analogous statistics for the velocity field.

[Phys. Rev. Fluids 3, 094603] Published Fri Sep 07, 2018

Expansion and retraction dynamics in drop-on-drop impacts on nonwetting surfaces

Thu, 09/06/2018 - 11:00

Author(s): Maher Damak and Kripa Varanasi

When a drop impacts a stationary drop on a non-wetting surface, the two drops coalesce, spread on the surface and retract, sometimes bouncing off. We measure the maximum diameter and retraction time for a wide range of parameter values and generalize known single drop models to drop-on-drop impacts.

[Phys. Rev. Fluids 3, 093602] Published Thu Sep 06, 2018

Reaction analogy based forcing for incompressible scalar turbulence

Thu, 09/06/2018 - 11:00

Author(s): Don Daniel, Daniel Livescu, and Jaiyoung Ryu

A new forcing method for generating statistically stationary scalar fields in incompressible turbulence is proposed based on an analogy with chemical reactions.

[Phys. Rev. Fluids 3, 094602] Published Thu Sep 06, 2018

Dielectrically driven convection in spherical gap geometry

Wed, 09/05/2018 - 11:00

Author(s): Florian Zaussinger, Peter Haun, Matthias Neben, Torsten Seelig, Vadim Travnikov, Christoph Egbers, Harunori Yoshikawa, and Innocent Mutabazi

Thermal convection in the spherical gap geometry induced by dielectric heating is studied by means of an extended thermoelectric hydrodynamics model. Numerical simulations based on this model are validated on the ISS experiment GeoFlow.

[Phys. Rev. Fluids 3, 093501] Published Wed Sep 05, 2018

Pairwise interactions in inertially driven one-dimensional microfluidic crystals

Wed, 09/05/2018 - 11:00

Author(s): Kaitlyn Hood and Marcus Roper

In microfluidic devices, inertia drives particles to focus on a streamline and form one-dimensional microfluidic crystals. Asymptotic theory for the pairwise particle interactions shows that particles assemble into stable equilibria, and the dynamics are analogous to the motion of a damped spring.

[Phys. Rev. Fluids 3, 094201] Published Wed Sep 05, 2018

Geometrical focusing of surface waves

Wed, 09/05/2018 - 11:00

Author(s): Gerardo Ruiz Chavarria, Patrice Le Gal, and Michael Le Bars

In an experimental investigation, water surface waves are focused at the Huygens’ cusp of a parabolic wave maker. Small amplitude waves behave linearly and similarly to light waves, following the diffraction laws. Large amplitude nonlinear waves are distorted by a large scale flow and focus before the expected cusp.

[Phys. Rev. Fluids 3, 094803] Published Wed Sep 05, 2018

Flow of wormlike micellar fluids around a sharp bend: Effects of branching and shear-banding

Tue, 09/04/2018 - 11:00

Author(s): Yiran Zhang, Hadi Mohammadigoushki, Margaret Y. Hwang, and Susan J. Muller

Flow transitions in wormlike micelle solutions flowing around a microfluidic 90° bend are studied. Shear-banding properties of the solution correlate with the form of secondary flow, while the micelle morphology (linear vs branched) has little effect on the flow behavior.

[Phys. Rev. Fluids 3, 093301] Published Tue Sep 04, 2018

Interaction of multiple drops and formation of toroidal-spiral particles

Tue, 09/04/2018 - 11:00

Author(s): Paola Leon Plata, Ying Liu, and Ludwig C. Nitsche

During sedimentation in a miscible, viscous liquid, polymeric drops self-assemble into a toroidal-spiral structure, which can be solidified by photoinitiated cross-linking. With a suitable arrangement three drops can be encapsulated, possibly enabling controlled release of a therapeutic drug cocktail.

[Phys. Rev. Fluids 3, 093601] Published Tue Sep 04, 2018

Scale dependence of kinetic helicity and selection of the axial dipole in rapidly rotating dynamos

Tue, 09/04/2018 - 11:00

Author(s): Binod Sreenivasan and Subhajit Kar

To understand why the magnetic fields of many planets are axial dipoles, the evolution in time of a seed magnetic field is studied using a dynamo model. The field is shown to excite helical convection, and the timescale for the growth in convection matches that for dipole formation.

[Phys. Rev. Fluids 3, 093801] Published Tue Sep 04, 2018