Physical Review Fluids

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Direct numerical simulation of flow over dissimilar, randomly distributed roughness elements: A systematic study on the effect of surface morphology on turbulence

Wed, 04/25/2018 - 11:00

Author(s): Pourya Forooghi, Alexander Stroh, Philipp Schlatter, and Bettina Frohnapfel

Direct numerical simulations of flow over fourteen dense rough walls with varying geometry are conducted. The effect of a departure from same-size element roughness on turbulence statistics is studied, and the correlation of the roughness function with wall-normal fluctuations at the roughness crest is examined.

[Phys. Rev. Fluids 3, 044605] Published Wed Apr 25, 2018

Effects of nonuniform viscosity on ciliary locomotion

Tue, 04/24/2018 - 11:00

Author(s): Kourosh Shoele and Patrick S. Eastham

The swimming efficiency of an idealized microswimmer is theoretically examined where the pointwise viscosity depends weakly on the surrounding nutrient. Results show that optimal swimming efficiency is achieved differently in the constant- and variable-viscosity cases.

[Phys. Rev. Fluids 3, 043101] Published Tue Apr 24, 2018

Scalar flux modeling in turbulent flames using iterative deconvolution

Mon, 04/23/2018 - 11:00

Author(s): Z. M. Nikolaou, R. S. Cant, and L. Vervisch

A novel approach for modeling the scalar flux term in turbulent flames is presented. An iterative algorithm is used for “deblurring” the filtered field. Successive iterations lead to improved approximations of the original field, and explicit filtering is then used for modeling the scalar flux.

[Phys. Rev. Fluids 3, 043201] Published Mon Apr 23, 2018

Investigation of the Klinkenberg effect in a micro/nanoporous medium by direct simulation Monte Carlo method

Fri, 04/20/2018 - 11:00

Author(s): Guang Yang and Bernhard Weigand

We define effective pore size as a function of the porosity, the tortuosity, the contraction factor, and the intrinsic permeability of the porous medium. The Klinkenberg effect in different porous structures is found to be fully described by the Knudsen number characterized by this pore size.

[Phys. Rev. Fluids 3, 044201] Published Fri Apr 20, 2018

Thermal convection of liquid sodium in inclined cylinders

Fri, 04/20/2018 - 11:00

Author(s): Ruslan Khalilov, Ilya Kolesnichenko, Alexander Pavlinov, Andrey Mamykin, Alexander Shestakov, and Peter Frick

The effect of inclination on the sodium (Pr=0.0094) turbulent convection in a cylinder of unit aspect ratio was studied experimentally for a fixed Rayleigh number Ra=(1.47±0.03)×107, and the inclination angle varied from 0° (the Rayleigh-Benard convection) up to 90° with a step of 10°.

[Phys. Rev. Fluids 3, 043503] Published Fri Apr 20, 2018

Experimental and numerical investigation of electrohydrodynamic flow in a point-to-ring corona discharge

Fri, 04/20/2018 - 11:00

Author(s): Yifei Guan, Ravi Sankar Vaddi, Alberto Aliseda, and Igor Novosselov

An electrohydrodynamic flow in a point-to-ring corona configuration is investigated experimentally and numerically. A parameter X, defined as the ratio of the local electric force to the inertial term, characterizes the effect of electrohydrodynamic forcing on bulk flow.

[Phys. Rev. Fluids 3, 043701] Published Fri Apr 20, 2018

Minimal formulation of the linear spatial analysis of capillary jets: Validity of the two-mode approach

Wed, 04/18/2018 - 11:00

Author(s): H. González, P. A. Vazquez, F. J. García, and J. Guerrero

Linear models are often used for the evolution of capillary jets. Here we present the simplest linear spatial formulation and compare it to numerical simulations. Two magnitudes, shape deformation, and mean axial velocity, and two spatial modes are needed, with one of them decaying exponentially.

[Phys. Rev. Fluids 3, 044802] Published Wed Apr 18, 2018

Fingering patterns in magnetic fluids: Perturbative solutions and the stability of exact stationary shapes

Tue, 04/17/2018 - 11:00

Author(s): Pedro H. A. Anjos, Sérgio A. Lira, and José A. Miranda

Pattern formation processes in magnetic fluids confined in a Hele-Shaw cell and subjected to a radial magnetic field are studied. It is shown that the weakly nonlinear flow drives an initially circular interface towards nontrivial exact stationary shapes, which are dynamically stable.

[Phys. Rev. Fluids 3, 044002] Published Tue Apr 17, 2018

Numerical simulations of thermal convection on a hemisphere

Mon, 04/16/2018 - 11:00

Author(s): C.-H. Bruneau, P. Fischer, Y.-L. Xiong, and H. Kellay (Cyclobulle Collaboration)

Original numerical simulations of 2D turbulent convection on a hemisphere are presented. Nusselt and Reynolds numbers verify scaling laws consistent with Rayleigh-Bénard convection. Despite significant differences in geometry with classical 3D cells, the scaling laws of thermal convection are robust.

[Phys. Rev. Fluids 3, 043502] Published Mon Apr 16, 2018

Spheroidal and conical shapes of ferrofluid-filled capsules in magnetic fields

Mon, 04/16/2018 - 11:00

Author(s): Christian Wischnewski and Jan Kierfeld

The numerical and analytical investigation of elastic capsules filled with a ferrofluid/dielectric liquid in a uniform magnetic/electric field shows a discontinuous spherical-to-conical shape transition for increasing fields with diverging strains in the conical tips.

[Phys. Rev. Fluids 3, 043603] Published Mon Apr 16, 2018

Instability-driven frequency decoupling between structure dynamics and wake fluctuations

Fri, 04/13/2018 - 11:00

Author(s): Yaqing Jin, Jin-Tae Kim, and Leonardo P. Chamorro

The interaction between wall-mounted, flexible plates and wake fluctuations is experimentally investigated as a function of several geometrical and flow parameters. It is demonstrated that significant decoupling between the dynamics of the structures and flow may occur because of near-wake flow instability.

[Phys. Rev. Fluids 3, 044701] Published Fri Apr 13, 2018

Topology of two-dimensional turbulent flows of dust and gas

Thu, 04/12/2018 - 11:00

Author(s): Dhrubaditya Mitra and Prasad Perlekar

In a study of inertial particle velocity gradients and the corresponding flow topology, the density weighted joint distribution shows that converging saddle structures are most probable.

[Phys. Rev. Fluids 3, 044303] Published Thu Apr 12, 2018

Multiscale analysis of the invariants of the velocity gradient tensor in isotropic turbulence

Wed, 04/11/2018 - 11:00

Author(s): Mohammad Danish and Charles Meneveau

A detailed study on the scale dependence of various quantities of interest, such as the population fraction of different flow-topologies, is presented. While the quantities appear close to scale invariant in inertial range, a “bump” is observed at length scales between the inertial and viscous ranges.

[Phys. Rev. Fluids 3, 044604] Published Wed Apr 11, 2018

Simulations of sheared dense noncolloidal suspensions: Evaluation of the role of long-range hydrodynamics

Mon, 04/09/2018 - 11:00

Author(s): Stany Gallier, François Peters, and Laurent Lobry

We find that the consequence of switching off long-range hydrodynamic interactions in simulations of concentrated suspension is that they can be switched off if considering the viscosity, but not if considering the diffusivity or particle velocities.

[Phys. Rev. Fluids 3, 042301(R)] Published Mon Apr 09, 2018

Unsteady sedimentation of a sphere in wormlike micellar fluids

Mon, 04/09/2018 - 11:00

Author(s): Yiran Zhang and Susan J. Muller

Flow transitions in the settling of a sphere in non-shear-banding wormlike micelle solutions are mapped. The onset of unsteady sedimentation correlates with an extensional Deborah number, while the velocity fluctuations are related to a shear Deborah number and an elastic Mach number.

[Phys. Rev. Fluids 3, 043301] Published Mon Apr 09, 2018

Response function of a moving contact line

Mon, 04/09/2018 - 11:00

Author(s): H. Perrin, D. Belardinelli, M. Sbragaglia, and B. Andreotti

How does a liquid-vapor interface in contact with a plate in motion react to the presence of defects at smaller scales? The hydrodynamics of such a system is investigated theoretically, offering a tractable mathematical framework to explore contact line motion through a disordered energy landscape.

[Phys. Rev. Fluids 3, 044001] Published Mon Apr 09, 2018

Solid-on-solid contact in a sphere-wall collision in a viscous fluid

Mon, 04/09/2018 - 11:00

Author(s): Sumit Kumar Birwa, G. Rajalakshmi, Rama Govindarajan, and Narayanan Menon

New experiments show that collisions between a sphere and a plane immersed in a viscous fluid involve direct mechanical contact, in contrast to expectations based on earlier theory. An electrical probe is used to monitor short-time mechanics of contact formation during the rebound of the sphere.

[Phys. Rev. Fluids 3, 044302] Published Mon Apr 09, 2018

Numerical study of turbulent channel flow perturbed by spanwise topographic heterogeneity: Amplitude and frequency modulation within low- and high-momentum pathways

Mon, 04/09/2018 - 11:00

Author(s): Ankit Awasthi and William Anderson

The feedback between topographically driven turbulent secondary flows and modulation of small-scale amplitude and frequency is explored. Results demonstrate that modulation remains but differs intrinsically because of background secondary flows within the domain.

[Phys. Rev. Fluids 3, 044602] Published Mon Apr 09, 2018

Impact of a small ellipticity on the sustainability condition of developed turbulence in a precessing spheroid

Mon, 04/09/2018 - 11:00

Author(s): Yasufumi Horimoto, Gabriel Simonet-Davin, Atsushi Katayama, and Susumu Goto

An experimental investigation shows that the small ellipticity of a precessing spheroidal cavity has a significant impact on the flow transition from solid-body rotational flow to developed turbulence of a confined fluid. In contrast, the developed turbulence in the spheroid is almost identical to that in the sphere.

[Phys. Rev. Fluids 3, 044603] Published Mon Apr 09, 2018

Turbulent thermal superstructures in Rayleigh-Bénard convection

Fri, 04/06/2018 - 11:00

Author(s): Richard J. A. M. Stevens, Alexander Blass, Xiaojue Zhu, Roberto Verzicco, and Detlef Lohse

Direct numerical simulations of highly turbulent Rayleigh-Bénard convection up to Rayleigh numbers Ra = 109 in horizontally periodic domains with aspect ratios up to Γ = 128, find superstructures of very large-scale and long living coherent structures.

[Phys. Rev. Fluids 3, 041501(R)] Published Fri Apr 06, 2018