Physical Review Fluids
Author(s): Sebastian Mühlbauer, Severin Strobl, and Thorsten Pöschel
In stochastic rotation dynamics the cubic interaction volumes induce artificial anisotropy, which can become significant in the vicinity of boundaries. A new study shows that this anisotropy can be avoided by employing randomly distributed, spherical interaction volumes instead of Cartesian grid cells.
[Phys. Rev. Fluids 2, 124204] Published Fri Dec 22, 2017
Author(s): Yi Man, William Page, Robert J. Poole, and Eric Lauga
Bacteria swim in viscous fluids by rotating helical flagellar filaments which dynamically bundle around each other. We derive and study a bundling model whereby straight rotating elastic filaments in viscous fluid induce rotational flows which tend to bend and wrap the filaments around each other.
[Phys. Rev. Fluids 2, 123101] Published Thu Dec 21, 2017
Author(s): A. Tilgner
Upper bounds E for the poloidal kinetic energy in thermal convection are derived from known bounds on the Nusselt number, and are improved by solving a separate optimization problem. The same procedure leads to a bound on the dissipation due to non poloidal velocity components.
[Phys. Rev. Fluids 2, 123502] Published Thu Dec 21, 2017
Author(s): A. Eden, C. McCallum, B. D. Storey, S. Pennathur, and C. D. Meinhart
A simulation of analyte preconcentration in a gated nanofluidic device finds that local field-effect control of surface properties can generate tunable ion concentration polarization regions in which anionic analytes are predicted to significantly accumulate if the electric double layers overlap.
[Phys. Rev. Fluids 2, 124203] Published Thu Dec 21, 2017
Author(s): Hiroshi Gotoda, Marc Pradas, and Serafim Kalliadasis
Time-series tools are used to analyze how chaotic dynamics interacts with noise in the generalized Kuramoto-Sivashinsky equation, a prototype for falling films. The critical value of the noise intensity for the chaotic-stochastic transition is quantified in terms of the system control parameter.
[Phys. Rev. Fluids 2, 124401] Published Thu Dec 21, 2017
Hierarchical micro- and nanofabrication by pattern-directed contact instabilities of thin viscoelastic films
Author(s): Abir Ghosh, Dipankar Bandyopadhyay, Jayati Sarkar, and Ashutosh Sharma
We propose that strategic use of an array of periodic patterns on a debonding contactor during elastic contact lithography can transform a flat polymer surface into a biomimetic super-hydrophobic surface having high-aspect ratio hierarchical patterns with tuneable adhesive properties.
[Phys. Rev. Fluids 2, 124004] Published Wed Dec 20, 2017
Author(s): Christoph Klopp, Ralf Stannarius, and Alexey Eremin
An experimental exploration of diffusive translational and rotational motions of elongated particles confined in a quasi-two-dimensional fluid is presented. Data obtained over 3 orders of magnitude in particle length demonstrate crossovers between hydrodynamical regimes determined by characteristic length scales.
[Phys. Rev. Fluids 2, 124202] Published Wed Dec 20, 2017
Author(s): James T. Jenkins and Michele Larcher
In dense, inclined flows of spheres, particles are often observed to translate in layers. The forces and rate of momentum transfer associated with a process of rub, lift, fall, and bump are calculated, and a relation between the ratio of shear stress to normal stress and the rate of strain is determined.
[Phys. Rev. Fluids 2, 124301] Published Wed Dec 20, 2017
Author(s): Y. H. Huang and M. R. Turner
An investigation of an N-vessel coupled sloshing system determines the existence of regions of parameter space where the (N+1)-fold 1:⋯:1 resonance can occur. These internal resonances are the precursors to the interesting dynamics in the nonlinear regime.
[Phys. Rev. Fluids 2, 124801] Published Wed Dec 20, 2017
Author(s): Pedro H. A. Anjos, Victor M. M. Alvarez, Eduardo O. Dias, and José A. Miranda
Most rotating Hele-Shaw cell studies assume a constant cell angular velocity and neglect inertial effects. This work considers a time-dependent angular velocity and includes inertia. These two new elements introduce important changes in the linear and weakly nonlinear dynamics of the problem.
[Phys. Rev. Fluids 2, 124003] Published Tue Dec 19, 2017
Author(s): Iain D. Boyd and Eswar Josyula
The effectiveness of a widely used phenomenological approach for modeling vibrational excitation is evaluated by comparison with a higher fidelity approach based on an ab initio computational chemistry analysis. A parameter is formulated to predict when the phenomenological approach is inaccurate.
[Phys. Rev. Fluids 2, 123401] Published Mon Dec 18, 2017
Author(s): M. Metzger, A. Fershtut, C. Kunkel, and J. Klewicki
Pocket events in the viscous sublayer of a turbulent boundary layer are shown to scale with the Taylor microscale. A simple model of a compact vortex propagating obliquely toward the wall from a position near the lower edge of the log layer is consistent with the observed scaling behavior.
[Phys. Rev. Fluids 2, 124602] Published Fri Dec 15, 2017
Author(s): Alejandro G. González and Patrick Weidman
A spatially modulated generalization of Taylor-Green vortices is obtained for Cartesian, polar, and cylindrical systems that are exact analytical solutions of the Navier-Stokes equation. It is shown that a double array of Taylor vortices mapped onto a cylinder may also have radial modulation.
[Phys. Rev. Fluids 2, 124701] Published Thu Dec 14, 2017
Author(s): Ahmed Ashour, Torsten Trittel, Tamás Börzsönyi, and Ralf Stannarius
Outflow of granular material from containers with small orifices is a ubiquitous phenomenon. A study using hydrogel spheres as templates of soft particles shows that the softness of the grains has considerable consequences: it changes the macroscopic dynamics qualitatively.
[Phys. Rev. Fluids 2, 123302] Published Wed Dec 13, 2017
Author(s): Enrico Chiarello, Anupam Gupta, Giampaolo Mistura, Mauro Sbragaglia, and Matteo Pierno
Droplet breakup in a microfluidic T junction is studied experimentally and numerically (3D) inside continuous phases made of shear-thinning solutions. In squeezing and dripping, the droplet length is found to scale with an effective capillary number, accounting for shear dependent viscosity.
[Phys. Rev. Fluids 2, 123602] Published Mon Dec 11, 2017
Author(s): Tristan Cambonie, Brahim Moudjed, Valéry Botton, Daniel Henry, and Hamda Ben Hadid
Acoustic streaming designates the ability to drive flows by acoustic propagation in dissipative fluids. We present an experimental study of a square flow driven by acoustic streaming. The flow evolution from steady to strongly unsteady is characterized, and a transition is observed between two regimes.
[Phys. Rev. Fluids 2, 123901] Published Fri Dec 08, 2017
Statistical characteristics of falling-film flows: A synergistic approach at the crossroads of direct numerical simulations and experiments
Author(s): Alexandros Charogiannis, Fabian Denner, Berend G. M. van Wachem, Serafim Kalliadasis, and Christos N. Markides
Based on experimental and numerical data from a wide range of flow conditions, relations linking the film-thickness statistics to the bulk-velocity statistics of wavy falling-film flows are developed from a Reynolds decomposition of the local time-varying film thickness and bulk velocity.
[Phys. Rev. Fluids 2, 124002] Published Fri Dec 08, 2017
Author(s): Rintaro Hayashi and Daisuke Takagi
Stokes flow is generated by repeatedly oscillating a pair of rigid rods. Table-top experiments and simulations reveal that a simple phase delay gives rise to complex flow patterns.
[Phys. Rev. Fluids 2, 124101] Published Fri Dec 08, 2017
Author(s): Simon J. Haward, Amy Q. Shen, Jacob Page, and Tamer A. Zaki
Experiments on flows through rectangular microchannels with a small amplitude sinusoidal profile on one wall confirm the existence of three regimes of perturbations that depend on the ratio of channel depth to roughness wavelength, α, and the dimensionless viscous length, θ, in agreement with theory.
[Phys. Rev. Fluids 2, 124102] Published Fri Dec 08, 2017
Author(s): S. Varchanis, Y. Dimakopoulos, and J. Tsamopoulos
An analysis of the conditions under which air bubbles may be trapped during the coating of microstructured substrates reveals, among other intriguing observations, that superhydrophobic flow patterns can arise even when the substrate is hydrophilic.
[Phys. Rev. Fluids 2, 124001] Published Thu Dec 07, 2017