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Physical Review Fluids
Number of Followers: 3  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Online) 2469-990X
Published by APS Homepage  [14 journals]
  • Numerical dispersion effects on the energy cascade in large-eddy
           simulation

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      Authors: Gopal R. Yalla; Todd A. Oliver, Robert D. Moser
      Abstract: Author(s): Gopal R. Yalla, Todd A. Oliver, and Robert D. Moser
      This work focuses on characterizing the effects of numerical dispersion error on the energy cascade in large-eddy simulation (LES) of convecting homogeneous isotropic turbulence. Numerical energy and transfer spectra reveal that energy is not transferred at the appropriate rate to wavemodes where significant dispersion error is present, leading to a deficiency of energy in highly dispersive modes and an accompanying pile up of energy in the well resolved modes. An asymptotic analysis indicates that dispersion error causes a phase decoherence between triad interacting wavemodes, leading to a reduction in the mean energy transfer rate for these scales.
      [Phys. Rev. Fluids 6, L092601] Published Mon Sep 27, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, L092601 (2021)
      PubDate: 2021-09-27T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L092601
      Issue No: Vol. 6, No. 9 (2021)
       
  • Ice front shaping by upward convective current

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      Authors: Ziqi Wang; Linfeng Jiang, Yihong Du, Chao Sun, Enrico Calzavarini
      Abstract: Author(s): Ziqi Wang, Linfeng Jiang, Yihong Du, Chao Sun, and Enrico Calzavarini
      The coupling between turbulent convecting water and the freezing/melting process leads to intriguingly complex phenomena which are of pressing importance for applications in environmental and climatological sciences. Here we study the extent and the morphology of ice forming in a differentially heated cavity filled with water by means of laboratory-scale experiments and numerical simulations. We demonstrate that the characteristic ice shape formed in our system is the result of the competition of two counterrotating convective rolls whose strength depends on the externally prescribed thermal gap.
      [Phys. Rev. Fluids 6, L091501] Published Tue Sep 14, 2021
      Keywords: Convection
      Citation: Phys. Rev. Fluids 6, L091501 (2021)
      PubDate: 2021-09-14T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L091501
      Issue No: Vol. 6, No. 9 (2021)
       
  • Predominance of pressure transport in spatial energy budget for a mixing
           layer approaching absolute instability

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      Authors: A. B. Aadhishwaran; Sourabh S. Diwan
      Abstract: Author(s): A. B. Aadhishwaran and Sourabh S. Diwan
      We examine the spatial energy budget for the plane incompressible mixing layer as the convective instability approaches absolute instability. Near onset of absolute instability pressure transport emerges as the primary mechanism responsible for the growth of disturbances, with the production mechanism making an insignificant contribution. Cross-stream profiles of production and pressure transport terms show significant changes in this limit, which are reflected in their contribution to the energy budget. These results, in particular the enhanced correlation between velocity and pressure disturbances, can help understand the physical processes causing absolute instability in a mixing layer.
      [Phys. Rev. Fluids 6, L091901] Published Mon Sep 13, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, L091901 (2021)
      PubDate: 2021-09-13T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L091901
      Issue No: Vol. 6, No. 9 (2021)
       
  • Purely viscous acoustic propulsion of bimetallic rods

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      Authors: Jeffrey McNeill; Nathan Sinai, Justin Wang, Vincent Oliver, Eric Lauga, François Nadal, Thomas E. Mallouk
      Abstract: Author(s): Jeffrey McNeill, Nathan Sinai, Justin Wang, Vincent Oliver, Eric Lauga, François Nadal, and Thomas E. Mallouk
      The rapid propulsion of metallic microrods at the nodal plane of an acoustic standing wave was first reported in 2012. Previous modeling proposed that the acoustic propulsion of metallic rods arises from the nonlinear inertial coupling between rotational and translational perturbation flows (acoustic streaming), but such a mechanism has yet to reproduce experimental data quantitatively. Here we report experiments on the acoustic propulsion of multi-segment bimetallic rods which are properly modeled by a purely viscous flapping mechanism where inertia plays no role.
      [Phys. Rev. Fluids 6, L092201] Published Fri Sep 10, 2021
      Keywords: Micro- and Nanofluidics
      Citation: Phys. Rev. Fluids 6, L092201 (2021)
      PubDate: 2021-09-10T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L092201
      Issue No: Vol. 6, No. 9 (2021)
       
  • Nonlinear shallow water dynamics with odd viscosity

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      Authors: Gustavo M. Monteiro; Sriram Ganeshan
      Abstract: Author(s): Gustavo M. Monteiro and Sriram Ganeshan
      The concept of an “odd” coefficient of viscosity appears in some fluid mechanical contexts, including quantum fluids, electron fluids in mesoscopic systems, as well as some classical systems. Here we study the shallow depth limit of weakly nonlinear surface dynamics with odd viscosity and gravitational effects and obtain an integrable Kortweg-de Vries equation, the solution of which admits right- and left-moving disturbances with some differences. The odd viscosity term plays a role similar to surface tension.
      [Phys. Rev. Fluids 6, L092401] Published Tue Sep 07, 2021
      Keywords: Nonlinear Dynamical Systems
      Citation: Phys. Rev. Fluids 6, L092401 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L092401
      Issue No: Vol. 6, No. 9 (2021)
       
  • Nonuniform mixing

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      Authors: Jean-Luc Thiffeault
      First page: 090501
      Abstract: Author(s): Jean-Luc Thiffeault
      Mixing in fluids is usually thought of as a process of homogenization, but in some circumstances, such as when dealing with filters, particles can have a tendency to accumulate, even at equilibrium. An example is virus particles kept out by a mask: they are more likely to be found near the filter because of a suction effect. A generalization of what we mean by mixing is called for, involving nonuniform, possibly time-dependent ultimate states.
      [Phys. Rev. Fluids 6, 090501] Published Mon Sep 13, 2021
      Keywords: Invited Articles
      Citation: Phys. Rev. Fluids 6, 090501 (2021)
      PubDate: 2021-09-13T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.090501
      Issue No: Vol. 6, No. 9 (2021)
       
  • Rayleigh-Bénard convection: The container shape matters

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      Authors: Olga Shishkina
      First page: 090502
      Abstract: Author(s): Olga Shishkina
      In an effort to achieve very large Rayleigh numbers when studying turbulence on a Rayleigh–Baposenard configuration, one can carry out simulations and experiments in as high convection cells as possible which involves using convection cells with the smallest possible aspect ratio. However, with the increasing height of the cell, the Rayleigh number grows much slower than the critical Rayleigh number for the onset of convection in the same container. This article discusses how to estimate accurately the critical Rayleigh number for the onset of convection in confined geometries and the optimal shape of the container.
      [Phys. Rev. Fluids 6, 090502] Published Tue Sep 28, 2021
      Keywords: Invited Articles
      Citation: Phys. Rev. Fluids 6, 090502 (2021)
      PubDate: 2021-09-28T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.090502
      Issue No: Vol. 6, No. 9 (2021)
       
  • Learning swimming escape patterns for larval fish under energy constraints

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      Authors: Ioannis Mandralis; Pascal Weber, Guido Novati, Petros Koumoutsakos
      First page: 093101
      Abstract: Author(s): Ioannis Mandralis, Pascal Weber, Guido Novati, and Petros Koumoutsakos
      This study explores escape motions employed by larval fish using two-dimensional simulations. We demonstrate how a deep reinforcement learning framework, discovers swimming escape motions, not previously obtained through direct optimization, under various energy constraints. The study serves to showcase the richness of flow physics that can be discovered through the use of artificial intelligence.
      [Phys. Rev. Fluids 6, 093101] Published Mon Sep 20, 2021
      Keywords: Biological and Biomedical Flows
      Citation: Phys. Rev. Fluids 6, 093101 (2021)
      PubDate: 2021-09-20T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093101
      Issue No: Vol. 6, No. 9 (2021)
       
  • Liquid transport produced by a cluster of peristaltic contractions in a
           circular channel

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      Authors: Tomoki Oyama; Shunichi Ishida, Kohei Maeyama, Taimei Miyagawa, Yohsuke Imai
      First page: 093102
      Abstract: Author(s): Tomoki Oyama, Shunichi Ishida, Kohei Maeyama, Taimei Miyagawa, and Yohsuke Imai
      Clustered contractions are observed in the human small intestine after fatty meals or in patients with gastrointestinal diseases. We present a numerical and theoretical analysis of liquid flow produced by the cluster of peristaltic waves in a circular channel. We show that flow rate is not proportional to the number of peristaltic waves in a cluster, and the flow rates of different numbers of waves collapse onto a single curve of each contraction ratio.
      [Phys. Rev. Fluids 6, 093102] Published Tue Sep 28, 2021
      Keywords: Biological and Biomedical Flows
      Citation: Phys. Rev. Fluids 6, 093102 (2021)
      PubDate: 2021-09-28T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093102
      Issue No: Vol. 6, No. 9 (2021)
       
  • Tollmien-Schlichting route to elastoinertial turbulence in channel flow

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      Authors: Ashwin Shekar; Ryan M. McMullen, Beverley J. McKeon, Michael D. Graham
      First page: 093301
      Abstract: Author(s): Ashwin Shekar, Ryan M. McMullen, Beverley J. McKeon, and Michael D. Graham
      Elastoinertial turbulence (EIT) in dilute polymer solutions displays tilted sheets of polymer stretch with weak spanwise-oriented flow structures – a sharp contrast to the three-dimensional quasistreamwise vortex structures that make up inertia-driven Newtonian turbulence. We show that at for channel flow at sufficiently high Reynolds number, the Newtonian nonlinear Tollmien-Schlichting (TS) wave evolves continuously into EIT as the Weissenberg number increases, highlighting in particular a “sheet-shedding” process by which individual sheets are born in the Kelvin cat’s eye structure of the TS wave and break up to form the layered multi-sheet structure characteristic of EIT.
      [Phys. Rev. Fluids 6, 093301] Published Mon Sep 27, 2021
      Keywords: Complex and Non-Newtonian Fluids
      Citation: Phys. Rev. Fluids 6, 093301 (2021)
      PubDate: 2021-09-27T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093301
      Issue No: Vol. 6, No. 9 (2021)
       
  • Propagation of two-dimensional vibroacoustic disturbances in a rarefied
           gas

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      Authors: A. Manela; Y. Ben-Ami
      First page: 093401
      Abstract: Author(s): A. Manela and Y. Ben-Ami
      The effect of gas rarefaction on the propagation of two-dimensional vibroacoustic disturbances generated by a nonuniformly oscillating plane is studied. Closed-form descriptions are obtained in the free-molecular (left panel of the figure) and continuum (right panel) limits and complemented by direct simulation Monte Carlo results. The impacts of gas rarefaction on signal decay rate and directivity pattern are highlighted and rationalized.
      [Phys. Rev. Fluids 6, 093401] Published Wed Sep 01, 2021
      Keywords: Compressible and Rarefied Flows, Kinetic Theory
      Citation: Phys. Rev. Fluids 6, 093401 (2021)
      PubDate: 2021-09-01T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093401
      Issue No: Vol. 6, No. 9 (2021)
       
  • Marginally stable thermal equilibria of Rayleigh-Bénard convection

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      Authors: Liam O'Connor; Daniel Lecoanet, Evan H. Anders
      First page: 093501
      Abstract: Author(s): Liam O'Connor, Daniel Lecoanet, and Evan H. Anders
      We study Boussinesq convection by computing marginally-stable mean temperature profiles for various Ra which are thermal equilibria of the quasilinear equations. We find these marginally-stable thermal equilibria by solving one-dimensional eigenvalue problems and allowing the mean temperature to evolve according to diffusion and advection by the eigenmodes. The mode amplitudes are chosen such that the mean temperature maintains marginally stability. We find that multiple marginally-stable modes become important for Ra> 106, and Nu ~ Ra1/3 up to our maximum Ra = 109.
      [Phys. Rev. Fluids 6, 093501] Published Tue Sep 21, 2021
      Keywords: Convection
      Citation: Phys. Rev. Fluids 6, 093501 (2021)
      PubDate: 2021-09-21T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093501
      Issue No: Vol. 6, No. 9 (2021)
       
  • Passage of surfactant-laden and particle-laden drops through a contraction

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      Authors: Franz De Soete; Léa Delance, Nicolas Passade-Boupat, Michael Levant, Emilie Verneuil, François Lequeux, Laurence Talini
      First page: 093601
      Abstract: Author(s): Franz De Soete, Léa Delance, Nicolas Passade-Boupat, Michael Levant, Emilie Verneuil, François Lequeux, and Laurence Talini
      The flow of either particle-laden or surfactant-laden drops through a contraction under an imposed pressure has been investigated in a microfluidic setup. The drop deformation generates surface concentration gradients in adsorbed species, which results in surface tension gradients. Crossing of the contraction is driven by the coupling between the drop flow and surface tension gradients and can result in larger passage times for surfactant-laden drops.
      [Phys. Rev. Fluids 6, 093601] Published Thu Sep 02, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 093601 (2021)
      PubDate: 2021-09-02T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093601
      Issue No: Vol. 6, No. 9 (2021)
       
  • Dynamics of a single free-settling spherical particle driven by a
           laser-induced bubble near a rigid boundary

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      Authors: Shengji Wu; Bo Li, Zhigang Zuo, Shuhong Liu
      First page: 093602
      Abstract: Author(s): Shengji Wu, Bo Li, Zhigang Zuo, and Shuhong Liu
      We systematically investigate the dynamics of a free-settling particle driven by a laser-induced bubble near a rigid boundary. Two types of particle-bubble interaction are identified, in terms of the intensity of the influence of the boundary on the particle-bubble dynamics. Two important phenomena where the particle ends up impacting on the boundary at a relatively high velocity are discovered, which provide a potential mechanism for enhanced cavitation erosion in sand-laden water.
      [Phys. Rev. Fluids 6, 093602] Published Fri Sep 03, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 093602 (2021)
      PubDate: 2021-09-03T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093602
      Issue No: Vol. 6, No. 9 (2021)
       
  • Wetting at nanoscale: Effect of surface forces and droplet size

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      Authors: Nikolai Kubochkin; Tatiana Gambaryan-Roisman
      First page: 093603
      Abstract: Author(s): Nikolai Kubochkin and Tatiana Gambaryan-Roisman
      The dependence of contact angle on droplet size for droplets of height of the order of a few nanometers has been intensively debated for decades. The size effects are believed to be related to surface forces. In the present work, we use the disjoining pressure concept and solve the Derjaguin equation in order to show that values of the contact angle are dramatically dependent on the droplet height as well as the way the contact angle is defined. For the first time, we demonstrate that different contact angle definitions can even lead to opposite dependencies of the contact angle on the droplet height.
      [Phys. Rev. Fluids 6, 093603] Published Fri Sep 10, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 093603 (2021)
      PubDate: 2021-09-10T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093603
      Issue No: Vol. 6, No. 9 (2021)
       
  • Coalescence characteristics of bulk nanobubbles in water: A molecular
           dynamics study coupled with theoretical analysis

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      Authors: Eric Bird; Eric Smith, Zhi Liang
      First page: 093604
      Abstract: Author(s): Eric Bird, Eric Smith, and Zhi Liang
      Nanobubble coalescence is a process of great importance to a broad range of applications such as froth flotation of fine or ultrafine mineral particles, detergent-free cleaning of clothes, and de-inking of recycled papers. To investigate the differences between nanobubble coalescence and macrobubble coalescence, we use molecular dynamics simulations and theoretical analysis to study the coalescence characteristics of bulk nanobubbles in water. We provide quantitative evidence showing nanobubble coalescence characteristics universally deviate from macroscopic bubble theories due to the small bubble size and the unique effects of Laplace pressure in nanobubbles.
      [Phys. Rev. Fluids 6, 093604] Published Tue Sep 14, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 093604 (2021)
      PubDate: 2021-09-14T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093604
      Issue No: Vol. 6, No. 9 (2021)
       
  • Kinematics of a bubble freely rising in a thin-gap cell with additional
           in-plane confinement

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      Authors: Lucas Pavlov; M. Verónica D'Angelo, Mario Cachile, Véronique Roig, Patricia Ern
      First page: 093605
      Abstract: Author(s): Lucas Pavlov, M. Verónica D'Angelo, Mario Cachile, Véronique Roig, and Patricia Ern
      Bubbles freely rising in a fluid at rest can display a variety of complex paths and shapes. We investigate experimentally their behavior in the inertial regimes obtained for a Hele-Shaw cell, where additional lateral walls are introduced to modify the cell width, and thus the coupling between the bubbles’ velocity and shape. Scaling laws characterizing the different regimes of motion are provided.
      [Phys. Rev. Fluids 6, 093605] Published Mon Sep 27, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 093605 (2021)
      PubDate: 2021-09-27T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093605
      Issue No: Vol. 6, No. 9 (2021)
       
  • Nonlinear behavior of electrohydrodynamic flow in viscoelastic fluids

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      Authors: Zheng-Gang Su; Tian-Fu Li, Kang Luo, Hong-Liang Yi
      First page: 093701
      Abstract: Author(s): Zheng-Gang Su, Tian-Fu Li, Kang Luo, and Hong-Liang Yi
      The nonlinear evolution of electrohydrodynamic flow subjected to unipolar injection in the dielectric liquid is extended from Newtonian fluids to viscoelastic fluids. The effect of viscoelasticity not only precipitates the onset of chaos but also leads to new transition sequences to chaos. Moreover, an asymmetric steady flow pattern is observed in a perfectly symmetric geometry. In viscoelastic fluids, the electric current transfer is reduced in most cases, but for weakly elastic fluid, it may be enhanced.
      [Phys. Rev. Fluids 6, 093701] Published Tue Sep 07, 2021
      Keywords: Electrokinetic Phenomena, Electrohydrodynamics, and Magnetohydrodynamics
      Citation: Phys. Rev. Fluids 6, 093701 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093701
      Issue No: Vol. 6, No. 9 (2021)
       
  • Interplay of induced charge electroosmosis and electrothermal flow in
           insulator-based dielectrophoresis

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      Authors: Amirreza Malekanfard; Zhijian Liu, Hui Zhao, Yongxin Song, Xiangchun Xuan
      First page: 093702
      Abstract: Author(s): Amirreza Malekanfard, Zhijian Liu, Hui Zhao, Yongxin Song, and Xiangchun Xuan
      A depth-averaged numerical model is developed to understand the experimentally observed interplay of induced charge electroosmosis and electrothermal flow in an insulator-based dielectrophoresis microdevice. The experimentally measured nonlinear fluid velocity matches asymptotically the predicted velocity of the electroosmotic flow in a low-concentration buffer and that of electrothermal flow in a high-concentration buffer. This agreement is consistent with a scaling analysis.
      [Phys. Rev. Fluids 6, 093702] Published Thu Sep 16, 2021
      Keywords: Electrokinetic Phenomena, Electrohydrodynamics, and Magnetohydrodynamics
      Citation: Phys. Rev. Fluids 6, 093702 (2021)
      PubDate: 2021-09-16T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093702
      Issue No: Vol. 6, No. 9 (2021)
       
  • Numerical study of the McIntyre instability around Gaussian floating
           vortices in thermal wind balance

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      Authors: Michael Le Bars
      First page: 093801
      Abstract: Author(s): Michael Le Bars
      The viscodiffusive McIntyre instability has been suggested as a possible source for density layer formation around laboratory and oceanic floating vortices. This suggestion is here quantitatively addressed using idealized, axisymmetric, numerical simulations of a simple Gaussian-like vortex in thermal wind balance, floating in a rotating, stratified flow.
      [Phys. Rev. Fluids 6, 093801] Published Tue Sep 07, 2021
      Keywords: Geophysical, Geological, Urban, and Ecological Flows
      Citation: Phys. Rev. Fluids 6, 093801 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093801
      Issue No: Vol. 6, No. 9 (2021)
       
  • Armstrong liquid bridge: Formation, evolution and breakup

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      Authors: Xueqin Pan; Man Hu, Bingrui Xu, Feng Wang, Peng Huo, Fangqi Chen, Zhibo Gu, Daosheng Deng
      First page: 093901
      Abstract: Author(s): Xueqin Pan, Man Hu, Bingrui Xu, Feng Wang, Peng Huo, Fangqi Chen, Zhibo Gu, and Daosheng Deng
      This work revisits the liquid bridge, which was observed by Lord William G. Armstrong in 1893, from a fresh perspective of its stability and final fate in terms of its lifetime. Remarkably, a water fall and the associated effective length are strongly correlated with the breakup of the liquid bridge. The linear stability analysis of an electrified jet agrees with experiments well. These results shed light on the underlying physical mechanism and on promising technological applications via active regulation and control of a liquid bridge.
      [Phys. Rev. Fluids 6, 093901] Published Thu Sep 02, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 093901 (2021)
      PubDate: 2021-09-02T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093901
      Issue No: Vol. 6, No. 9 (2021)
       
  • Pulse modulation of synthetic jet actuators for control of separation

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      Authors: Thomas T. Rice; Keith Taylor, Michael Amitay
      First page: 093902
      Abstract: Author(s): Thomas T. Rice, Keith Taylor, and Michael Amitay
      We investigate vortex shedding off an airfoil generated by pulsed actuation (or pulse modulation) of synthetic jets. This technique is shown to shed circulation in a controlled manner during dynamic stall, reducing many of its detrimental effects.
      [Phys. Rev. Fluids 6, 093902] Published Fri Sep 24, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 093902 (2021)
      PubDate: 2021-09-24T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.093902
      Issue No: Vol. 6, No. 9 (2021)
       
  • Surfactant-driven instability of a divergent flow

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      Authors: G. Koleski; J.-C. Loudet, A. Vilquin, B. Pouligny, T. Bickel
      First page: 094001
      Abstract: Author(s): G. Koleski, J.-C. Loudet, A. Vilquin, B. Pouligny, and T. Bickel
      The flow of a submerged water jet directed toward the liquid interface is investigated both experimentally and theoretically. We find evidence that the presence of a small amount of surfactants can trigger an azimuthal instability. Our theoretical model reveals that surfactant advection in the Stokes regime contains the minimal ingredients to explain the instability.
      [Phys. Rev. Fluids 6, 094001] Published Tue Sep 07, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 094001 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094001
      Issue No: Vol. 6, No. 9 (2021)
       
  • Bifurcation study for a surface-acoustic-wave-driven meniscus

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      Authors: Kevin David Joachim Mitas; Ofer Manor, Uwe Thiele
      First page: 094002
      Abstract: Author(s): Kevin David Joachim Mitas, Ofer Manor, and Uwe Thiele
      The deposition of homogeneous and patterned films of partially wetting liquid from a liquid meniscus driven by Rayleigh surface acoustic waves (SAW) is analyzed with a thin-film model. Employing path continuation and time simulation we investigate, in particular, how the time-periodic states corresponding to line deposition and the related bifurcations emerge when changing the Weber number or the SAW strength describing scenarios relevant for a class of deposition and coating processes.
      [Phys. Rev. Fluids 6, 094002] Published Wed Sep 15, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 094002 (2021)
      PubDate: 2021-09-15T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094002
      Issue No: Vol. 6, No. 9 (2021)
       
  • Autonomous transport and splitting of a droplet on an open surface

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      Authors: Imdad Uddin Chowdhury; Pallab Sinha Mahapatra, Ashis Kumar Sen, Arvind Pattamatta, Manish K. Tiwari
      First page: 094003
      Abstract: Author(s): Imdad Uddin Chowdhury, Pallab Sinha Mahapatra, Ashis Kumar Sen, Arvind Pattamatta, and Manish K. Tiwari
      We show a standalone power-free technique for transporting and splitting a droplet on an open surface using continuous wettability-gradients. A three-dimensional phase-field Cahn-Hilliard model for interfaces and Navier-Stokes equations for transport are employed and solved numerically using the finite element method. We can control the droplet splitting ratio by manipulating the widths of the Y-branches. The physics of the droplet transport, flow pattern inside the droplet, and the splitting mechanisms have been explained through detailed numerical studies and scaling analysis.
      [Phys. Rev. Fluids 6, 094003] Published Mon Sep 27, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 094003 (2021)
      PubDate: 2021-09-27T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094003
      Issue No: Vol. 6, No. 9 (2021)
       
  • Collective surfing of two self-propelled swimmers at liquid-air interface
           aided by self-induced Marangoni flow

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      Authors: Prajitha Mottammal; Sumesh P. Thampi, Andrey Pototsky
      First page: 094004
      Abstract: Author(s): Prajitha Mottammal, Sumesh P. Thampi, and Andrey Pototsky
      We study collective motion of two hydrodynamically coupled identical pushers at a planar fluid/air interface in the presence of self-induced Marangoni flow, which is generated by insoluble surfactant, excreted by the pushers at a constant rate. Surfactant decomposes homogeneously at a constant rate. Under specific initial conditions, the pushers form a stable rotational equilibrium, whereby each pusher follows a circular path and the distribution of surfactant in the co-rotating frame of reference is stationary. In the absence of the Marangoni flow, the rotational equilibrium becomes unstable and the pushers move away from each other.
      [Phys. Rev. Fluids 6, 094004] Published Tue Sep 28, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 094004 (2021)
      PubDate: 2021-09-28T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094004
      Issue No: Vol. 6, No. 9 (2021)
       
  • Shape of spreading and leveling gravity currents in a Hele-Shaw cell with
           flow-wise width variation

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      Authors: Zhong Zheng; Aditya A. Ghodgaonkar, Ivan C. Christov
      First page: 094101
      Abstract: Author(s): Zhong Zheng, Aditya A. Ghodgaonkar, and Ivan C. Christov
      Self-similarity is a universality phenomenon exhibited from large scales (e.g., supernovae) to small scales (e.g., spreading of droplets). Viscous gravity currents in nonuniform passages exhibit an “incomplete” version of such universality. This combined theoretical–numerical–experimental study provides a theory of the dependence of the universal dynamics on the initial and boundary conditions, and demonstrates two distinct incomplete self-similar regimes in the spreading and leveling of a viscous gravity current.
      [Phys. Rev. Fluids 6, 094101] Published Fri Sep 10, 2021
      Keywords: Laminar and Viscous Flows
      Citation: Phys. Rev. Fluids 6, 094101 (2021)
      PubDate: 2021-09-10T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094101
      Issue No: Vol. 6, No. 9 (2021)
       
  • Splash of impacting nanodroplets on solid surfaces

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      Authors: Yi-Bo Wang; Yi-Feng Wang, Xin Wang, Ben-Xi Zhang, Yan-Ru Yang, Duu-Jong Lee, Xiao-Dong Wang, Min Chen
      First page: 094201
      Abstract: Author(s): Yi-Bo Wang, Yi-Feng Wang, Xin Wang, Ben-Xi Zhang, Yan-Ru Yang, Duu-Jong Lee, Xiao-Dong Wang, and Min Chen
      Using molecular dynamics simulations we study the splash of water nanodroplets (ND) on hydrophilic to hydrophobic surfaces. Mechanisms for internal breakup and prompt splash are found to be different from those of macroscale (MS) impacting droplets. Breakup is attributed to initial air holes on solid surfaces for MS, but to vibration of a nanometer spreading film for ND. The prompt splash is initiated by air bubbles under spreading lamella at MS, but for ND by Rayleigh-Taylor instability of ejected rims from rapidly decelerated spreading lamella. ND internal breakup depends on surface wettability because vibration attenuation is larger on hydrophilic than hydrophobic surfaces.
      [Phys. Rev. Fluids 6, 094201] Published Fri Sep 03, 2021
      Keywords: Micro- and Nanofluidics
      Citation: Phys. Rev. Fluids 6, 094201 (2021)
      PubDate: 2021-09-03T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094201
      Issue No: Vol. 6, No. 9 (2021)
       
  • Diffusive and capillary instabilities of viscous fluid threads in
           microchannels

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      Authors: Thomas Cubaud; Bryan Conry, Xiaoyi Hu, Thai Dinh
      First page: 094202
      Abstract: Author(s): Thomas Cubaud, Bryan Conry, Xiaoyi Hu, and Thai Dinh
      We experimentally investigate the flow behavior of viscous oil threads in a a variety of miscible and immiscible low-molecular weight alcohols in microchannels. A comparative study is conducted between diffusive and capillary regimes using simple functional relationships for the thread characteristics, including diameter and detachment length. We develop a comprehensive classification of immiscible and miscible fluid dynamics in square microfluidic channels and provide a quantitative analysis of the evolution of multiphase flow properties across flow patterns.
      [Phys. Rev. Fluids 6, 094202] Published Tue Sep 07, 2021
      Keywords: Micro- and Nanofluidics
      Citation: Phys. Rev. Fluids 6, 094202 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094202
      Issue No: Vol. 6, No. 9 (2021)
       
  • Electrohydrodynamic migration and dispersion of polyelectrolytes during
           simultaneous shear flow and electrophoresis

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      Authors: Dmitry I. Kopelevich; Jason E. Butler
      First page: 094203
      Abstract: Author(s): Dmitry I. Kopelevich and Jason E. Butler
      Simultaneous application of flow and electric fields along a microfluidic channel can focus flexible polyelectrolyte molecules. Electrohydrodynamic interactions drive the migration to the center. Though migration velocity increases monotonically with electric field strength, the polyelectrolyte concentration at the center of the channel diminishes after exceeding a critical electric field. The mean-field model developed here demonstrates that dispersion, induced by the electric field interacting with Brownian fluctuations in the polyelectrolyte configuration, causes this phenomena.
      [Phys. Rev. Fluids 6, 094203] Published Wed Sep 22, 2021
      Keywords: Micro- and Nanofluidics
      Citation: Phys. Rev. Fluids 6, 094203 (2021)
      PubDate: 2021-09-22T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094203
      Issue No: Vol. 6, No. 9 (2021)
       
  • Onset of grain motion in eroding subaqueous bimodal granular beds

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      Authors: Marios Galanis; Philip Wang, Mark D. Shattuck, Corey S. O'Hern, Nicholas T. Ouellette
      First page: 094301
      Abstract: Author(s): Marios Galanis, Philip Wang, Mark D. Shattuck, Corey S. O'Hern, and Nicholas T. Ouellette
      The effect of grain size on the critical shear stress required to initiate sediment transport in erodible granular beds is typically described by the Shields number which compares the hydrodynamic stress to the particle weight. Although this framework works well for beds composed of grains of the same size, we find that it does not capture the behavior of polydisperse beds. In particular, we find that larger grains are mobilized by nominally subcritical stresses when small grains are present. Our results highlight the importance of granular contact and force networks in controlling the onset of sediment transport.
      [Phys. Rev. Fluids 6, 094301] Published Tue Sep 07, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 094301 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094301
      Issue No: Vol. 6, No. 9 (2021)
       
  • Dynamics of phase separation of sheared binary mixtures after a
           nonisothermal quenching

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      Authors: Antonio Bertei; Chih-Che Chueh, Roberto Mauri
      First page: 094302
      Abstract: Author(s): Antonio Bertei, Chih-Che Chueh, and Roberto Mauri
      A thermodynamics-based phase-field model is developed to simulate phase separation of a binary mixture under a temperature gradient in a constant shear. The effects of meaningful dimensionless numbers, such as the capillary number, the Lewis number, and the dimensionless heat capacity are explored. The temperature gradient breaks the symmetry of phase separation compared to instantaneous quenching while different phase separation patterns, ranging from stripes to drops, can be obtained or even suppressed by a proper choice of parameters.
      [Phys. Rev. Fluids 6, 094302] Published Wed Sep 08, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 094302 (2021)
      PubDate: 2021-09-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094302
      Issue No: Vol. 6, No. 9 (2021)
       
  • Hydrodynamic torque on a slender cylinder rotating perpendicularly to its
           symmetry axis

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      Authors: Jean-Lou Pierson; Mohammed Kharrouba, Jacques Magnaudet
      First page: 094303
      Abstract: Author(s): Jean-Lou Pierson, Mohammed Kharrouba, and Jacques Magnaudet
      The torque experienced by a circular cylinder rotating steadily about an axis passing trough its centroid and perpendicular to its symmetry axis is computed over a wide range of Reynolds number and aspect ratios using fully resolved simulations. In the creeping-flow regime, numerical results are shown to match predictions of an improved slender-body approximation. In strongly inertial regimes, flow symmetries and boundary layer arguments are employed to derive scaling laws for the various contributions to the torque. We finally obtain an empirical formula for the total torque, valid throughout the parameter range explored in the simulations.
      [Phys. Rev. Fluids 6, 094303] Published Wed Sep 08, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 094303 (2021)
      PubDate: 2021-09-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094303
      Issue No: Vol. 6, No. 9 (2021)
       
  • Ternary phase-field simplified multiphase lattice Boltzmann method and its
           application to compound droplet dynamics on solid surface in shear flow

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      Authors: Z. Chen; C. Shu, Y. Y. Liu, L. Q. Zhang
      First page: 094304
      Abstract: Author(s): Z. Chen, C. Shu, Y. Y. Liu, and L. Q. Zhang
      A ternary phase-field simplified multiphase lattice Boltzmann method (TPF-SMLBM) is developed in a numerical investigation of a compound droplet placed on solid substrate in shear flow at moderate Reynolds numbers. Three major kinematic modes are recovered: quasi-steady sliding (QSS), tumbling-sliding, and tumbling-detachment. Analysis of QSS dynamics explains the wetting length exponential shrinking rate in the early evolution stage. A new dimensionless parameter, the Tumbling number (Tu), is proposed to identify the mode transition towards tumbling. The dynamics of detachment is also investigated, showing that the critical Capillary number of detachments can be described by a scaling law.
      [Phys. Rev. Fluids 6, 094304] Published Thu Sep 09, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 094304 (2021)
      PubDate: 2021-09-09T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094304
      Issue No: Vol. 6, No. 9 (2021)
       
  • Promoting global stability in data-driven models of quadratic nonlinear
           dynamics

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      Authors: Alan A. Kaptanoglu; Jared L. Callaham, Aleksandr Aravkin, Christopher J. Hansen, Steven L. Brunton
      First page: 094401
      Abstract: Author(s): Alan A. Kaptanoglu, Jared L. Callaham, Aleksandr Aravkin, Christopher J. Hansen, and Steven L. Brunton
      Modeling realistic fluid and plasma flows is computationally intensive, motivating the use of reduced-order models for a variety of scientific and engineering tasks. However, it is challenging to characterize, much less guarantee, the global stability (i.e., long-time boundedness) of these models. In this work, we illustrate how to modify the objective function in machine learning algorithms to promote globally stable data-driven models of fluid and plasma flows. This innovation significantly extends the applicability of sparse system identification for complex dynamics, such as models of turbulent boundary layers.
      [Phys. Rev. Fluids 6, 094401] Published Tue Sep 07, 2021
      Keywords: Nonlinear Dynamical Systems
      Citation: Phys. Rev. Fluids 6, 094401 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094401
      Issue No: Vol. 6, No. 9 (2021)
       
  • Taylor dispersion of elongated rods

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      Authors: Ajay Harishankar Kumar; Stuart J. Thomson, Thomas R. Powers, Daniel M. Harris
      First page: 094501
      Abstract: Author(s): Ajay Harishankar Kumar, Stuart J. Thomson, Thomas R. Powers, and Daniel M. Harris
      In many complex fluids, the geometry of particles in suspension can be complex, prompting the need to understand how shape influences their bulk transport. We consider the Taylor dispersion of passive, elongated Brownian rods subject to a background Poiseuille flow. Monte-Carlo simulations demonstrate that elongated particles exhibit enhanced longitudinal dispersion compared to their spherical counterparts, in excellent agreement with integral expressions derived from asymptotic analysis. For particles of high aspect-ratio, the dispersion coefficient can be collapsed along a single curve, providing a simple correction factor that extends Taylor’s seminal results to elongated particles.
      [Phys. Rev. Fluids 6, 094501] Published Tue Sep 07, 2021
      Keywords: Transport and Mixing
      Citation: Phys. Rev. Fluids 6, 094501 (2021)
      PubDate: 2021-09-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094501
      Issue No: Vol. 6, No. 9 (2021)
       
  • Investigation of properties of superfluid $^{4}\mathrm{He}$ turbulence
           using a hot-wire signal

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      Authors: P. Diribarne; M. Bon Mardion, A. Girard, J.-P. Moro, B. Rousset, F. Chilla, J. Salort, A. Braslau, F. Daviaud, B. Dubrulle, B. Gallet, I. Moukharski, E.-W. Saw, C. Baudet, M. Gibert, P.-E. Roche, E. Rusaouen, Andrei Golov, Victor L'vov, Sergey Nazarenko
      First page: 094601
      Abstract: Author(s): P. Diribarne, M. Bon Mardion, A. Girard, J.-P. Moro, B. Rousset, F. Chilla, J. Salort, A. Braslau, F. Daviaud, B. Dubrulle, B. Gallet, I. Moukharski, E.-W. Saw, C. Baudet, M. Gibert, P.-E. Roche, E. Rusaouen, Andrei Golov, Victor L'vov, and Sergey Nazarenko
      We report hot-wire measurements in flows of high and low turbulence intensities, both in normal and superfluid helium, at 1.6 K, 2 K, and 2.3 K. Consistent with previous studies, we observe a spectral bump at high frequency. Surprisingly, the bump frequency is found to depend on the turbulence intensity of the flow. Using the turbulent Reynolds number rather than the velocity as a control parameter collapses results from both flows.
      [Phys. Rev. Fluids 6, 094601] Published Wed Sep 08, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 094601 (2021)
      PubDate: 2021-09-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094601
      Issue No: Vol. 6, No. 9 (2021)
       
  • Direct numerical simulation of compressible turbulence in a counter-flow
           channel configuration

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      Authors: Arash Hamzehloo; David J. Lusher, Sylvain Laizet, Neil D. Sandham
      First page: 094603
      Abstract: Author(s): Arash Hamzehloo, David J. Lusher, Sylvain Laizet, and Neil D. Sandham
      We introduce a counter-flow turbulent channel configuration, amenable to simulation and modeling. It has periodic streamwise and spanwise boundaries and isothermal no-slip walls. A tangent hyperbolic forcing function drives the flow in opposite directions on the upper and lower halves of the channel, forming an antisymmetric mean shear velocity profile. Compared to conventional channel flows, the mean flow is inflectional and the maximum turbulence intensity relative to the maximum mean velocity is nearly an order of magnitude higher. The counter-flow channel can sustain high turbulent Mach numbers which is useful for studying high Reynolds and Mach number turbulent flows.
      [Phys. Rev. Fluids 6, 094603] Published Thu Sep 09, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 094603 (2021)
      PubDate: 2021-09-09T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094603
      Issue No: Vol. 6, No. 9 (2021)
       
  • Asymptotic approximations for swirling turbulent plume rising from
           circular sources

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      Authors: Yuchen Dai; Alexander Klimenko, Yuanshen Lu, Kamel Hooman
      First page: 094604
      Abstract: Author(s): Yuchen Dai, Alexander Klimenko, Yuanshen Lu, and Kamel Hooman
      Swirling turbulent plumes are investigated with the Morton, Taylor, and Turner model (MTT) and the Γ-approach. We derive the asymptotic solutions using regular perturbation methods, and discuss the influence of swirling motions on the plume properties for lazy and forced plumes, respectively. Specially and intriguingly, by introducing a swirl, a forced plume can even be turned into a lazy one in the near field during the vertical evolution.
      [Phys. Rev. Fluids 6, 094604] Published Fri Sep 10, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 094604 (2021)
      PubDate: 2021-09-10T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094604
      Issue No: Vol. 6, No. 9 (2021)
       
  • Transportation and coherent structures in MHD turbulent channel flow
           subject to uniform streamwise and spanwise magnetic fields

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      Authors: Olivier Doche; Sedat Tardu, Jonathan Schillings, Amandine Capogna
      First page: 094605
      Abstract: Author(s): Olivier Doche, Sedat Tardu, Jonathan Schillings, and Amandine Capogna
      We study the effect of both uniform spanwise and streamwise magnetic fields on the near wall region of a turbulent channel flow. Previous results have shown that the spanwise magnetic field leads to flow relaminarization for magnetic intensity significantly smaller than the streamwise magnetic field. In order to explain these results, a deep analysis of the fine turbulence structure is needed. We perform a detailed analysis through the Reynolds shear-stress transport equations and the conditional averaging deduced from the near wall active eddies, thus connecting the magnetic field orientation effect to the coherent electric current topology.
      [Phys. Rev. Fluids 6, 094605] Published Tue Sep 14, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 094605 (2021)
      PubDate: 2021-09-14T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094605
      Issue No: Vol. 6, No. 9 (2021)
       
  • Wavelet-based adaptive wall-modeled large eddy simulation method for
           compressible turbulent flows

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      Authors: Xuan Ge; Oleg V. Vasilyev, M. Yousuff Hussaini
      First page: 094606
      Abstract: Author(s): Xuan Ge, Oleg V. Vasilyev, and M. Yousuff Hussaini
      We develop a wavelet-based adaptive wall-modeled large eddy simulation (WA-WMLES) method to overcome the stringent restriction on step size for time integration, caused by mesh resolution requirement to resolve inner viscous sublayer, which becomes computationally expensive as the Reynolds number increases. This approach uses a wavelet-based adaptive large eddy simulation, incorporated into the anisotropic-adaptive wavelet collocation framework, to resolve the outer region of turbulent boundary layer, while the inner part is approximated by the wall-shear-stress model, and extends the application of the wavelet-based adaptive methods to a realistic wall-bounded turbulent flow configuration at a relatively high (order of a million) Reynolds number.
      [Phys. Rev. Fluids 6, 094606] Published Tue Sep 14, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 094606 (2021)
      PubDate: 2021-09-14T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094606
      Issue No: Vol. 6, No. 9 (2021)
       
  • Physics-informed machine learning of the Lagrangian dynamics of velocity
           gradient tensor

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      Authors: Yifeng Tian; Daniel Livescu, Michael Chertkov
      First page: 094607
      Abstract: Author(s): Yifeng Tian, Daniel Livescu, and Michael Chertkov
      Reduced models describing the Lagrangian dynamics of the Velocity Gradient Tensor (VGT) in Homogeneous Isotropic Turbulence (HIT) are developed under the Physics-Informed Machine Learning (PIML) framework. We construct the pressure Hessian and sub-filter contributions using the integrity bases and invariants of VGT and express them with extended Tensor Basis Neural Network (TBNN). We observe that the PIML model provides an improved representation for the magnitude and orientation of the small-scale pressure Hessian contributions. Statistics of the flow, as indicated by the joint PDF of second and third invariants of the VGT, show good agreement with the “ground-truth” DNS data.
      [Phys. Rev. Fluids 6, 094607] Published Thu Sep 23, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 094607 (2021)
      PubDate: 2021-09-23T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094607
      Issue No: Vol. 6, No. 9 (2021)
       
  • Wind wave growth in the viscous regime

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      Authors: Jiarong Wu; Luc Deike
      First page: 094801
      Abstract: Author(s): Jiarong Wu and Luc Deike
      How water surface waves grow under wind forcing has long been an interesting and challenging question. For short gravity-capillary waves, the viscous effects are important but have not been well studied. In this paper, we simulate the wind-wave growth by directly solving the two-phase Navier-Stokes equations. The numerical method features a momentum conserving scheme, interface reconstruction using Volume of Fluid, and adaptive mesh refinement (AMR). As a result, we observe concurrent growth of the irrotational traveling wave and the rotational drift layer (current). The growth rate of the wave and the evolution of the drift layer under different forcing parameters are discussed respectively.
      [Phys. Rev. Fluids 6, 094801] Published Wed Sep 08, 2021
      Keywords: Wave Dynamics, Free Surface Flows, Stratified, and Rotating Flows
      Citation: Phys. Rev. Fluids 6, 094801 (2021)
      PubDate: 2021-09-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.094801
      Issue No: Vol. 6, No. 9 (2021)
       
  • Reciprocal theorem for calculating the flow rate–pressure drop relation
           for complex fluids in narrow geometries

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      Authors: Evgeniy Boyko; Howard A. Stone
      Abstract: Author(s): Evgeniy Boyko and Howard A. Stone
      A key aspect in understanding pressure-driven flows of non-Newtonian fluids in narrow and confined geometries is the relationship between the flow rate and pressure drop. Using the Lorentz reciprocal theorem, we derive a closed-form expression for the flow rate-pressure drop relation of complex fluids in narrow channels of arbitrary shape, which holds for a wide class of viscoelastic and shear-thinning constitutive models. For the weakly non-Newtonian limit, our theory provides the first-order non-Newtonian correction for the flow rate-pressure drop relation solely using the corresponding Newtonian solution, eliminating the need to solve the non-Newtonian flow problem.
      [Phys. Rev. Fluids 6, L081301] Published Thu Aug 26, 2021
      Keywords: Complex and Non-Newtonian Fluids
      Citation: Phys. Rev. Fluids 6, L081301 (2021)
      PubDate: 2021-08-26T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L081301
      Issue No: Vol. 6, No. 8 (2021)
       
  • Unexpected scaling of interstitial velocities with permeability due to
           polymer retention in porous media

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      Authors: Shima Parsa; Ahmad Zareei, Enric Santanach-Carreras, Eliza J. Morris, Ariel Amir, Lizhi Xiao, David A. Weitz
      Abstract: Author(s): Shima Parsa, Ahmad Zareei, Enric Santanach-Carreras, Eliza J. Morris, Ariel Amir, Lizhi Xiao, and David A. Weitz
      Flow and retention of polymer in porous media result in an unexpected reduction in medium permeability. Our experiment and simulation of polymer retention show that these changes are a direct consequence of pore blockage and diversion of flow through the medium. Despite the complex changes in flow after polymer retention, we introduce a simple scaling for the distribution of pore-level velocities based on the bulk permeability of the medium.
      [Phys. Rev. Fluids 6, L082302] Published Wed Aug 25, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, L082302 (2021)
      PubDate: 2021-08-25T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L082302
      Issue No: Vol. 6, No. 8 (2021)
       
  • Symmetry analysis of the turbulent dissipation rate

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      Authors: Kalale Chola; Pinaki Chakraborty
      Abstract: Author(s): Kalale Chola and Pinaki Chakraborty
      In 1935, G. I. Taylor invoked rotational symmetry to derive a remarkable formula for the turbulent dissipation rate. That derivation, though ingenious, leaves it unclear if the formula truly conforms with rotational symmetry. We use the machinery of Lie groups to furnish a rigorous derivation of Taylor’s formula under rotational symmetry and also under a symmetry not considered by Taylor, reflectional symmetry.
      [Phys. Rev. Fluids 6, L082602] Published Thu Aug 19, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, L082602 (2021)
      PubDate: 2021-08-19T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L082602
      Issue No: Vol. 6, No. 8 (2021)
       
  • Model reduction of traveling-wave problems via Radon cumulative
           distribution transform

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      Authors: Jie Ren; William R. Wolf, Xuerui Mao
      Abstract: Author(s): Jie Ren, William R. Wolf, and Xuerui Mao
      Due to their sizeable Kolmogorov n-width, travel-wave problems have brought critical challenges to conventional model reduction techniques. This study aims to provide new insights into this problem by exploiting the Radon cumulative distribution transform (R-CDT) that emerged in the sector of computer vision science. By virtue of the unique property that nonlinear invertible R-CDT renders both traveling and scaling components into amplitude modulations, a substantial model-reduction is achieved in the R-CDT space, while sustaining high accuracy. The method is parameter-free and data-driven, which lends itself to problems regardless of the dimensions or boundary conditions.
      [Phys. Rev. Fluids 6, L082501] Published Tue Aug 17, 2021
      Keywords: Transport and Mixing
      Citation: Phys. Rev. Fluids 6, L082501 (2021)
      PubDate: 2021-08-17T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L082501
      Issue No: Vol. 6, No. 8 (2021)
       
  • Wall-curvature driven dynamics of a microswimmer

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      Authors: Chaithanya K. V. S.; Sumesh P. Thampi
      First page: 083101
      Abstract: Author(s): Chaithanya K. V. S. and Sumesh P. Thampi
      We study the dynamics of a microswimmer near a wall with arbitrary curvature using theory and lattice Boltzmann simulations. The results are presented using several measures with experimental relevance. Extending the previous works on swimmer dynamics near a flat wall, we comprehensively explore the swimmer dynamics near flat, concave, and convex walls. We find that swimmers exhibit a greater affinity towards a concave boundary compared to a convex boundary. In addition, the combined effect of convex and concave walls is studied by confining the swimmer in an annulus.
      [Phys. Rev. Fluids 6, 083101] Published Mon Aug 16, 2021
      Keywords: Biological and Biomedical Flows
      Citation: Phys. Rev. Fluids 6, 083101 (2021)
      PubDate: 2021-08-16T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083101
      Issue No: Vol. 6, No. 8 (2021)
       
  • Dynamics of a helical swimmer crossing viscosity gradients

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      Authors: Christian Esparza López; Jorge Gonzalez-Gutierrez, Francisco Solorio-Ordaz, Eric Lauga, Roberto Zenit
      First page: 083102
      Abstract: Author(s): Christian Esparza López, Jorge Gonzalez-Gutierrez, Francisco Solorio-Ordaz, Eric Lauga, and Roberto Zenit
      We study how helical swimmers move across a viscosity gradient, motivated by the need to understand how such heterogenous environments affect the motion of microorganisms. We find that the swimmer’s speed can be either decreased or increased while crossing the viscosity gradient, depending on the orientation of the tail and the gradient of viscosity. Our experimental findings are sustained by good agreement with a resistive-force based model.
      [Phys. Rev. Fluids 6, 083102] Published Mon Aug 23, 2021
      Keywords: Biological and Biomedical Flows
      Citation: Phys. Rev. Fluids 6, 083102 (2021)
      PubDate: 2021-08-23T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083102
      Issue No: Vol. 6, No. 8 (2021)
       
  • Shock-induced combustion of aluminum particle clusters investigated with
           resolved sharp-interface two-dimensional simulations

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      Authors: Pratik Das; H. S. Udaykumar
      First page: 083201
      Abstract: Author(s): Pratik Das and H. S. Udaykumar
      The combustion of aluminum particle clusters in shocked flows is studied with two-dimensional numerical simulations. These simulations examine, for the first time, aspects of the vaporization and burning of molten aluminum particle clusters that are markedly different from an isolated burning aluminum particle. The flame-structure around a particle within a cluster is found to vary along the flow direction: particles at the cluster front end undergo kinetically limited combustion with the formation of a wake flame, while particles located downstream in the cluster burn with an envelope flame indicating combustion limited by transport and mixing.
      [Phys. Rev. Fluids 6, 083201] Published Mon Aug 30, 2021
      Keywords: Combustion Fluid Mechanics and Reacting Flows
      Citation: Phys. Rev. Fluids 6, 083201 (2021)
      PubDate: 2021-08-30T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083201
      Issue No: Vol. 6, No. 8 (2021)
       
  • Developing horizontal convection against stable temperature stratification
           in a rectangular container

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      Authors: Daisuke Noto; Tomomi Terada, Takatoshi Yanagisawa, Takehiro Miyagoshi, Yuji Tasaka
      First page: 083501
      Abstract: Author(s): Daisuke Noto, Tomomi Terada, Takatoshi Yanagisawa, Takehiro Miyagoshi, and Yuji Tasaka
      Developing stages of horizontal convection observed during transitions from conduction to thermally equilibrated convection states are studied with visualization experiments imposing horizontally differential heating at the top of low-temperature water. Due to the absence of destabilizing thermal sources, convective rolls, which are localized on the horizontal plane on which differential heating is imposed, are formed only by the baroclinic torque driving force against a braking force due to stable temperature stratification. We find a nondimensional parameter for the balance of the braking force relaxing with time and the baroclinic torque driving force.
      [Phys. Rev. Fluids 6, 083501] Published Wed Aug 25, 2021
      Keywords: Convection
      Citation: Phys. Rev. Fluids 6, 083501 (2021)
      PubDate: 2021-08-25T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083501
      Issue No: Vol. 6, No. 8 (2021)
       
  • Actuating water droplets on liquid infused surfaces: A rickshaw for
           droplets

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      Authors: Christophe Raufaste; Simon J. Cox, Franck Celestini
      First page: 083603
      Abstract: Author(s): Christophe Raufaste, Simon J. Cox, and Franck Celestini
      An efficient actuation method for millimetric droplets is described: Single droplets are driven on a liquid infused surface by a small bead that acts as a carrier, like a rickshaw. When the bead is moved at a fixed velocity the droplet follows its trajectory, up to a critical value of the velocity at which the bead and the droplet lose contact. The critical velocity is predicted from a balance between the bead/droplet adhesion force and the friction acting on the droplet where it is in contact with the substrate.
      [Phys. Rev. Fluids 6, 083603] Published Wed Aug 11, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 083603 (2021)
      PubDate: 2021-08-11T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083603
      Issue No: Vol. 6, No. 8 (2021)
       
  • Emptying-filling boxes with non-Boussinesq plumes and fountains

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      Authors: R. Mehaddi; P. Boulet, M. Koutaiba, O. Vauquelin, F. Candelier
      First page: 083801
      Abstract: Author(s): R. Mehaddi, P. Boulet, M. Koutaiba, O. Vauquelin, and F. Candelier
      When a light fluid is continuously released from the top (as a fountain) or from the bottom (as a plume) into a box with a top opening, a buoyant layer of constant thickness and density forms under the ceiling at steady state. Both configurations have been investigated using theoretical approaches and small scale air-helium experiments. As a practical application, for a fixed buoyant flux, the fountain and the plume configurations have been compared with respect to their mixing efficiency.
      [Phys. Rev. Fluids 6, 083801] Published Wed Aug 25, 2021
      Keywords: Geophysical, Geological, Urban, and Ecological Flows
      Citation: Phys. Rev. Fluids 6, 083801 (2021)
      PubDate: 2021-08-25T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083801
      Issue No: Vol. 6, No. 8 (2021)
       
  • Linear theory of particulate Rayleigh-Bénard instability

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      Authors: Suryansh Prakhar; Andrea Prosperetti
      First page: 083901
      Abstract: Author(s): Suryansh Prakhar and Andrea Prosperetti
      Particles falling uniformly through a Rayleigh-Bénard cell have a profound influence on the stability of the system. Mechanically, they exert a stabilizing effect akin to that of the solid phase in a porous medium. Their temperature, however, can markedly affect the undisturbed temperature distribution of the fluid phase with unexpected effects on the stability threshold.
      [Phys. Rev. Fluids 6, 083901] Published Wed Aug 11, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 083901 (2021)
      PubDate: 2021-08-11T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083901
      Issue No: Vol. 6, No. 8 (2021)
       
  • Stability of a thin viscoelastic film falling down an inclined plane

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      Authors: Tao Hu; Qing-fei Fu, Yan Xing, Li-jun Yang, Luo Xie
      First page: 083902
      Abstract: Author(s): Tao Hu, Qing-fei Fu, Yan Xing, Li-jun Yang, and Luo Xie
      We study the long-wave instability of a falling film of the Oldroyd-B fluid. The weighted residual method is adopted to model the film dynamics in both linear and nonlinear regimes. The mechanism of the viscoelastic effect on the instability is explored within the framework of the Whitham wave hierarchy theory. We further analyze the film evolution and the traveling waves by means of nonlinear simulations.
      [Phys. Rev. Fluids 6, 083902] Published Thu Aug 12, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 083902 (2021)
      PubDate: 2021-08-12T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083902
      Issue No: Vol. 6, No. 8 (2021)
       
  • Beyond actuator line arrays in active flow control studies: Lessons from a
           genetic algorithm approach

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      Authors: Fernando Zigunov; Prabu Sellappan, Farrukh Alvi
      First page: 083903
      Abstract: Author(s): Fernando Zigunov, Prabu Sellappan, and Farrukh Alvi
      Active flow control with microjets in crossflow is a promising technology to improve the performance of many engineering flows. Predicting effective placement for the microjets at the surface of the aerodynamic model remains an unsolved challenge due to the complex interactions between the jets and the main flow. We propose and demonstrate a fully experimental, model-free approach using a solenoid array and a genetic algorithm to find a highly effective actuator pattern for drag reduction in the flow over a simplified fuselage afterbody, deploying thousands of actuator configurations in a single experiment and reaching a configuration that achieves a 10% reduction in drag.
      [Phys. Rev. Fluids 6, 083903] Published Mon Aug 23, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 083903 (2021)
      PubDate: 2021-08-23T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.083903
      Issue No: Vol. 6, No. 8 (2021)
       
  • Relaxation of a fluid-filled blister on a porous substrate

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      Authors: Danielle L. Chase; Ching-Yao Lai, Howard A. Stone
      First page: 084101
      Abstract: Author(s): Danielle L. Chase, Ching-Yao Lai, and Howard A. Stone
      We study the relaxation dynamics of a fluid-filled blister between an elastic sheet and a porous substrate using laboratory experiments and a mathematical model. The dynamics are controlled by the deformation of the elastic sheet, the viscous stresses in the pores, and the capillary pressure at the liquid-air interface due to imbibition. We identify two regimes of drainage, where for thick sheets and more permeable substrates, drainage is primarily due to the stresses in the deformed elastic sheet, and for thin sheets and less permeable substrates, drainage is driven by the imbibition of the liquid into the pore space.
      [Phys. Rev. Fluids 6, 084101] Published Wed Aug 18, 2021
      Keywords: Laminar and Viscous Flows
      Citation: Phys. Rev. Fluids 6, 084101 (2021)
      PubDate: 2021-08-18T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084101
      Issue No: Vol. 6, No. 8 (2021)
       
  • Alignment of a flexible platelike particle in shear flow: Effect of
           surface slip and edges

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      Authors: Catherine Kamal; Simon Gravelle, Lorenzo Botto
      First page: 084102
      Abstract: Author(s): Catherine Kamal, Simon Gravelle, and Lorenzo Botto
      Rigid plate-like particles displaying interfacial slip can attain a constant orientation in a shear flow when the slip length is sufficiently large. But actual thin particles such as single-layer graphene are prone to bending deformations when exposed to shear stress. To study the effect of bending deformation on the particle’s stable orientation, we develop a two-dimensional fluid-structure interaction model. We find that (i) a stable alignment occurs even for relatively flexible particles, and that (ii) edges effects on the shape of the plate are important for values of the length-to-thickness aspect ratio as large as 100.
      [Phys. Rev. Fluids 6, 084102] Published Wed Aug 18, 2021
      Keywords: Laminar and Viscous Flows
      Citation: Phys. Rev. Fluids 6, 084102 (2021)
      PubDate: 2021-08-18T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084102
      Issue No: Vol. 6, No. 8 (2021)
       
  • Attraction and repulsion between objects in a granular flow

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      Authors: G. A. Caballero-Robledo; M. F. Acevedo-Escalante, F. Mandujano, C. Málaga
      First page: 084303
      Abstract: Author(s): G. A. Caballero-Robledo, M. F. Acevedo-Escalante, F. Mandujano, and C. Málaga
      For the first time, the lift force on a pair of obstacles placed side-by-side within a granular flow is studied experimentally. Attraction or repulsion exists between the obstacles depending on the flow velocity and the distance separating them. We found an interesting empirical relation between the lift force and the flow velocity around the obstacles. Our analysis supports the idea that the granular system behaves like a pair of hot intruders within a Newtonian fluid flow with temperature-dependent viscosity.
      [Phys. Rev. Fluids 6, 084303] Published Fri Aug 13, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 084303 (2021)
      PubDate: 2021-08-13T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084303
      Issue No: Vol. 6, No. 8 (2021)
       
  • Droplet aerobreakup under the shear-induced entrainment regime using a
           multiscale two-fluid approach

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      Authors: Georgia Nykteri; Manolis Gavaises
      First page: 084304
      Abstract: Author(s): Georgia Nykteri and Manolis Gavaises
      A droplet exposed to a high-speed gas flow is subject to a violent fragmentation, dominated by a widespread mist of multiscale structures that introduce significant complexities in numerical studies. The present work focuses on capturing all stages of the aerodynamic breakup of a waterlike droplet under the shear-induced entrainment regime. The numerical investigation is conducted within a physically consistent multiscale framework, which provides insight into the mist dynamics and the distribution of the produced secondary droplets under different postshock conditions.
      [Phys. Rev. Fluids 6, 084304] Published Tue Aug 17, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 084304 (2021)
      PubDate: 2021-08-17T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084304
      Issue No: Vol. 6, No. 8 (2021)
       
  • Multiphase CFD modeling of front propagation in a Hele-Shaw cell featuring
           a localized constriction

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      Authors: Jonatan R. Mac Intyre; Antti Puisto, Marko Korhonen, Mikko Alava, Jordi Ortín
      First page: 084305
      Abstract: Author(s): Jonatan R. Mac Intyre, Antti Puisto, Marko Korhonen, Mikko Alava, and Jordi Ortín
      Liquid-gas front propagation in disordered media exhibits unique behavior during a repeated series of drainage-imbibition displacements. Such complex behavior in a disordered media can be simplified to a single mesa-shaped defect, which provides new insight into the collective behavior at the macro-scale. We show how the morphological difference in imbibition and drainage is affected by the capillary number and wetting properties.
      [Phys. Rev. Fluids 6, 084305] Published Tue Aug 17, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 084305 (2021)
      PubDate: 2021-08-17T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084305
      Issue No: Vol. 6, No. 8 (2021)
       
  • Comparison of the properties of segregated layers in a bidispersed
           fluidized bed to those of a monodispersed fluidized bed

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      Authors: Yinuo Yao; Craig S. Criddle, Oliver B. Fringer
      First page: 084306
      Abstract: Author(s): Yinuo Yao, Craig S. Criddle, and Oliver B. Fringer
      Since industrial fluidized-bed reactors typically operate with polydispersed particles, approximating such reactors as the superposition of corresponding monodispersed fluidized beds would greatly simplify their design and operation. To examine the validity of this superposition, we evaluate the effects of bidispersity by comparing three-dimensional liquid-solid monodispersed and segregated bidipsersed fluidized beds. This work demonstrates that, despite the clear segregation into layers that behave like monodispersed beds, the transition region is governed by complex bidispersed mechanisms that cannot be explained in terms of the particle behavior in the segregated layers.
      [Phys. Rev. Fluids 6, 084306] Published Fri Aug 27, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 084306 (2021)
      PubDate: 2021-08-27T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084306
      Issue No: Vol. 6, No. 8 (2021)
       
  • Transient aggregation of particles at interfaces

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      Authors: Antoine Lagarde; Christophe Josserand, Suzie Protière
      First page: 084307
      Abstract: Author(s): Antoine Lagarde, Christophe Josserand, and Suzie Protière
      The formation of an axisymmetric monolayer of dense particles at a liquid interface is explored in order to study the interaction between numerous objects of different sizes randomly distributed on a liquid surface. The individual motion of each bead cannot be solved but the overall clustering can be described statistically. The clustering dynamics of this system with a long-range interaction varies during the aggregation process. The cluster-size distribution evolves with a self-similar mechanism and we observe a well-defined transition between two aggregating regimes that we can characterize.
      [Phys. Rev. Fluids 6, 084307] Published Fri Aug 27, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 084307 (2021)
      PubDate: 2021-08-27T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084307
      Issue No: Vol. 6, No. 8 (2021)
       
  • Local relaminarization mechanism induced by a dynamic free-slip boundary

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      Authors: Cong Wang; Morteza Gharib
      First page: 084604
      Abstract: Author(s): Cong Wang and Morteza Gharib
      Wall-attached dynamic free-slip surfaces effectively shift the near-wall transverse vorticity field and associated turbulent shearing motions away, creating a locally relaminarized zone in the near-wall region of the turbulent boundary layer.
      [Phys. Rev. Fluids 6, 084604] Published Thu Aug 12, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084604 (2021)
      PubDate: 2021-08-12T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084604
      Issue No: Vol. 6, No. 8 (2021)
       
  • Structure functions in nocturnal atmospheric boundary layer turbulence

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      Authors: Eliezer Kit; Eli Barami, H. J. S. Fernando
      First page: 084605
      Abstract: Author(s): Eliezer Kit, Eli Barami, and H. J. S. Fernando
      Turbulence in a nocturnal stably stratified flow draining from a mountain range was captured using a probe system consisting of sonic and hot-film anemometers that communicate with each other through a neural network for optimal operation without any human intervention. This unique ‘Combo’ system allowed probing turbulence continuously down to energy dissipation scales, at Taylor Reynolds number greater than 1200. The data analyses, together with direct numerical simulation, reveal that, contrary to the Kolmogorov Self-Similarity Hypothesis, turbulence at dissipation scales is anisotropic, suggesting a new line of inquiry on turbulence in stable atmospheric boundary layers.
      [Phys. Rev. Fluids 6, 084605] Published Tue Aug 17, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084605 (2021)
      PubDate: 2021-08-17T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084605
      Issue No: Vol. 6, No. 8 (2021)
       
  • Numerical study of Fourier-filtered rough surfaces

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      Authors: F. Alves Portela; A. Busse, N. D. Sandham
      First page: 084606
      Abstract: Author(s): F. Alves Portela, A. Busse, and N. D. Sandham
      Correlations between the properties of a rough surface and their associated drag are a very useful tool in engineering. Here, we assess the effect of different scales of roughness by numerically simulating the flow over surfaces constructed by band-passing the spectral content of a scanned grit-blasted surface. Although the velocity fluctuations are found overall to be resilient to the changes, we find existing drag correlations to be only qualitatively useful, while dispersive stresses (associated with mean flow inhomogeneity) are shown to depend on the roughness spectral content.
      [Phys. Rev. Fluids 6, 084606] Published Fri Aug 20, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084606 (2021)
      PubDate: 2021-08-20T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084606
      Issue No: Vol. 6, No. 8 (2021)
       
  • Effects of porous walls on near-wall supersonic turbulence

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      Authors: Yongkai Chen; Carlo Scalo
      First page: 084607
      Abstract: Author(s): Yongkai Chen and Carlo Scalo
      Modification to the structure of wall-bounded turbulence due to the presence of porous walls has been investigated in the low and high supersonic regime. For sufficiently high degrees of wall permeability, streamwise-traveling surface waves are triggered and stay confined in the buffer layer region. These waves yield a sinusoidal modulation of the near-wall turbulent ejection and burst events.
      [Phys. Rev. Fluids 6, 084607] Published Mon Aug 23, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084607 (2021)
      PubDate: 2021-08-23T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084607
      Issue No: Vol. 6, No. 8 (2021)
       
  • Bifurcation structure of unstable periodic orbits in plane Couette flow
           with the Smagorinsky model

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      Authors: Eiichi Sasaki; Genta Kawahara, Javier Jiménez
      First page: 084608
      Abstract: Author(s): Eiichi Sasaki, Genta Kawahara, and Javier Jiménez
      To study the dynamical properties of plane Couette turbulence, this paper describes unstable periodic orbits (UPOs) in a large eddy simulation (LES) system with a Smagorinsky-type eddy viscosity model. At a moderately high Reynolds number, the UPO of the present study possesses spanwise vortices in the central region of the channel, which seem to be caused by a streak instability. These stretched vortices are shown to enhance transfer of the streamwise turbulent momentum, as in developed near-wall turbulence.
      [Phys. Rev. Fluids 6, 084608] Published Wed Aug 25, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084608 (2021)
      PubDate: 2021-08-25T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084608
      Issue No: Vol. 6, No. 8 (2021)
       
  • Direct numerical simulation of turbulent elliptical pipe flow under system
           rotation about the major axis

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      Authors: Rafael Hurtado Rosas; Zhao-Ping Zhang, Bing-Chen Wang
      First page: 084609
      Abstract: Author(s): Rafael Hurtado Rosas, Zhao-Ping Zhang, and Bing-Chen Wang
      The effect of Coriolis forces on the turbulent flow in an elliptical pipe subjected to spanwise rotation has been studied using direct numerical simulations (DNS). In response to the system rotation, large-scale secondary flows appear in the cross-stream plane as a pair of counter-rotating vortices, which significantly impact the turbulence statistics and structures of the flow. The characteristics of the turbulence field is investigated in both physical and spectral spaces through analyses of the first- and second-order statistical moments, as well as the budget balance of the Reynolds stress transport equation and coherent flow structures.
      [Phys. Rev. Fluids 6, 084609] Published Wed Aug 25, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084609 (2021)
      PubDate: 2021-08-25T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084609
      Issue No: Vol. 6, No. 8 (2021)
       
  • Conformal invariance of the 1-point statistics of the zero-isolines of
           $2d$ scalar fields in inverse turbulent cascades

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      Authors: M. Wacławczyk; V. N. Grebenev, M. Oberlack
      First page: 084610
      Abstract: Author(s): M. Wacławczyk, V. N. Grebenev, and M. Oberlack
      For three decades there have been speculations about the existence of conformal invariance in two-dimensional turbulence and possible implications thereof. These speculations have been confirmed by numerical experiments. However, there is a scarcity of relevant analytical studies on this topic. In our work we analyze the underlying equation for the one-point probability density function of a scalar in two-dimensional turbulence. We derive conditions under which the probability measure is conformally invariant and show that with this transformation certain statistics of non-homogeneous fields can be derived based on solutions of the homogeneous one.
      [Phys. Rev. Fluids 6, 084610] Published Thu Aug 26, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084610 (2021)
      PubDate: 2021-08-26T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084610
      Issue No: Vol. 6, No. 8 (2021)
       
  • Large-scale structures of scalar and velocity in a turbulent jet flow

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      Authors: Jesse Reijtenbagh; Jerry Westerweel, Willem van de Water
      First page: 084611
      Abstract: Author(s): Jesse Reijtenbagh, Jerry Westerweel, and Willem van de Water
      In a turbulent jet flow, finite-time Lyapunov exponents gauge the exponentially fast spreading of fluid parcels. To observe their fine structure, we moved our Particle Image Velocimetry and Laser-Induced Fluorescence cameras with the mean flow. The resulting remarkable shapes in the figure are linked to the organization of a dispersed fluorescent tracer.
      [Phys. Rev. Fluids 6, 084611] Published Thu Aug 26, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084611 (2021)
      PubDate: 2021-08-26T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084611
      Issue No: Vol. 6, No. 8 (2021)
       
  • Artificial neural network approach for turbulence models: A local
           framework

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      Authors: Chenyue Xie; Xiangming Xiong, Jianchun Wang
      First page: 084612
      Abstract: Author(s): Chenyue Xie, Xiangming Xiong, and Jianchun Wang
      The Reynolds-averaged Navier-Stokes (RANS) unclosed terms can be reconstructed by the local artificial neural network (LANN) based on the local coordinate system which is orthogonal to the curved wall. The LANN model performs better than the Global artifical neural network (GANN), Spalart-Allmaras (SA), and Shear Stress Transport (SST) k−ω models in the predictions of the average velocity, wall-shear stress, and average pressure in the flows over periodic hills. The LANN framework has a great potential to be applied to complex wall-bounded turbulent flows over curved walls.
      [Phys. Rev. Fluids 6, 084612] Published Tue Aug 31, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 084612 (2021)
      PubDate: 2021-08-31T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084612
      Issue No: Vol. 6, No. 8 (2021)
       
  • Resolvent analysis of stratification effects on wall-bounded shear flows

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      Authors: M. A. Ahmed; H. J. Bae, A. F. Thompson, B. J. McKeon
      First page: 084804
      Abstract: Author(s): M. A. Ahmed, H. J. Bae, A. F. Thompson, and B. J. McKeon
      The resolvent framework for the Navier-Stokes equations with the Boussinesq approximation was applied to a stratified turbulent boundary layer. The results show that despite using only a very limited range of representative scales, the resolvent model was able to reproduce the relative magnitude of turbulence intensities and the balance of the energy budget as well as provide meaningful analysis of structures in the flow. The resolvent response modes were able to predict the relative variation in turbulence intensities as a function of wall-normal distance and Richardson number (Riτ) for the Riτ under consideration in this study.
      [Phys. Rev. Fluids 6, 084804] Published Wed Aug 11, 2021
      Keywords: Wave Dynamics, Free Surface Flows, Stratified, and Rotating Flows
      Citation: Phys. Rev. Fluids 6, 084804 (2021)
      PubDate: 2021-08-11T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084804
      Issue No: Vol. 6, No. 8 (2021)
       
  • Spanwise structuring and rivulet formation in suspended falling liquid
           films

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      Authors: Manuel Rietz; Reinhold Kneer, Benoit Scheid, Wilko Rohlfs
      First page: 084805
      Abstract: Author(s): Manuel Rietz, Reinhold Kneer, Benoit Scheid, and Wilko Rohlfs
      In thin films flowing down the underside of an inclined planar substrate, surface topology is known to evolve towards a spanwise structuring of rivulets. While experiments imply a connection between long-term spanwise structuring and primary instabilities (PI) of the film surface at low Reynolds number (Re), this connection is not conclusive if a larger parameter space of Re and Kapitza number (Ka) is considered. Using an integral boundary layer model for falling liquid films and varying imposed initial conditions, Re, Ka, and wall inclination, we numerically investigate long-term rivulet evolution and its connection to PI, obtaining excellent concordance with previous experimental data.
      [Phys. Rev. Fluids 6, 084805] Published Wed Aug 25, 2021
      Keywords: Wave Dynamics, Free Surface Flows, Stratified, and Rotating Flows
      Citation: Phys. Rev. Fluids 6, 084805 (2021)
      PubDate: 2021-08-25T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.084805
      Issue No: Vol. 6, No. 8 (2021)
       
  • Erratum: Quantized orbital-chasing liquid metal heterodimers directed by
           an integrated pilot-wave field [Phys. Rev. Fluids 5, 053603 (2020)]

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      Authors: Jianbo Tang; Xi Zhao, Jing Liu
      First page: 089902
      Abstract: Author(s): Jianbo Tang, Xi Zhao, and Jing Liu
      [Phys. Rev. Fluids 6, 089902] Published Tue Aug 17, 2021
      Keywords: Errata
      Citation: Phys. Rev. Fluids 6, 089902 (2021)
      PubDate: 2021-08-17T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.089902
      Issue No: Vol. 6, No. 8 (2021)
       
  • Irreversibility and rate dependence in sheared adhesive suspensions

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      Authors: Zhouyang Ge; Raffaella Martone, Luca Brandt, Mario Minale
      Abstract: Author(s): Zhouyang Ge, Raffaella Martone, Luca Brandt, and Mario Minale
      Experiments and simulations of a non-Brownian suspension of particles demonstrate that weak van der Waals (adhesive) interactions induce rate dependence of the rheological response in oscillatory shear flow, with enhanced particle diffusivities and cluster formations below a critical shear rate, even though the steady shear behavior remains rate-independent. Phase diagrams showing the influence of volume fraction, strain amplitude, and oscillation frequency, for a given Hamaker constant, highlight the connection between irreversibility and suspension rheology.
      [Phys. Rev. Fluids 6, L101301] Published Wed Oct 13, 2021
      Keywords: Complex and Non-Newtonian Fluids
      Citation: Phys. Rev. Fluids 6, L101301 (2021)
      PubDate: 2021-10-13T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L101301
      Issue No: Vol. 6, No. 10 (2021)
       
  • Marginal regeneration-induced drainage of surface bubbles

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      Authors: Jonas Miguet; Marina Pasquet, Florence Rouyer, Yuan Fang, Emmanuelle Rio
      Abstract: Author(s): Jonas Miguet, Marina Pasquet, Florence Rouyer, Yuan Fang, and Emmanuelle Rio
      When a soap film drains, marginal regeneration refers to the rise of patches that are thinner than the rest of the film. In this work the rise velocities and sizes of buoyant patches are measured and found to be in good agreement with a Rayleigh-Taylor like instability and a model based on a balance of gravitational and surface viscous forces, as suggested in the literature. Thus, in an environment saturated in humidity, to eliminate evaporation effects, marginal regeneration approximately describes the film drainage at the apex of a draining bubble.
      [Phys. Rev. Fluids 6, L101601] Published Wed Oct 06, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, L101601 (2021)
      PubDate: 2021-10-06T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L101601
      Issue No: Vol. 6, No. 10 (2021)
       
  • Fluid dynamics beyond the continuum: A physical perspective on large-eddy
           simulation

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      Authors: Max Okraschevski; Sven Hoffmann, Katharina Stichling, Rainer Koch, Hans-Joerg Bauer
      Abstract: Author(s): Max Okraschevski, Sven Hoffmann, Katharina Stichling, Rainer Koch, and Hans-Joerg Bauer
      In our work, we motivate and rederive the Large-eddy simulation (LES) framework by coarse-graining of Lagrangian fluid elements making use of a statistical mechanics approach. Consequently, we understand that LES is much more than a numerical turbulence model, namely a perspective commonly taken by modern fluid dynamicists, not only in numerical simulations but also in experiments. From this point of view, we see the potential to develop a unified theory for LES and the Reynolds-averaged Navier-Stokes (RANS) framework and additionally reveal a link to uncertainty quantification in particle image velocimetry (PIV).
      [Phys. Rev. Fluids 6, L102601] Published Mon Oct 04, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, L102601 (2021)
      PubDate: 2021-10-04T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.L102601
      Issue No: Vol. 6, No. 10 (2021)
       
  • From limited observations to the state of turbulence: Fundamental
           difficulties of flow reconstruction

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      Authors: Tamer A. Zaki; Mengze Wang
      First page: 100501
      Abstract: Author(s): Tamer A. Zaki and Mengze Wang
      Is it possible to reconstruct all the scales of turbulence from limited observations? If so, what is the minimum resolution of observations for a successful reconstruction? How much information about a turbulent flow field can be decoded from an isolated, instantaneous measurement? These fundamental questions are addressed using variational data assimilation, where the observations are infused in simulations and are decoded using the Navier-Stokes equations. We highlight the “dual butterfly effect” and how the stochasticity of turbulence obfuscates the interpretation of measurements.
      [Phys. Rev. Fluids 6, 100501] Published Wed Oct 06, 2021
      Keywords: Invited Articles
      Citation: Phys. Rev. Fluids 6, 100501 (2021)
      PubDate: 2021-10-06T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.100501
      Issue No: Vol. 6, No. 10 (2021)
       
  • Wave damping by flexible marsh plants influenced by current

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      Authors: Xiaoxia Zhang; Heidi Nepf
      First page: 100502
      Abstract: Author(s): Xiaoxia Zhang and Heidi Nepf
      We develop a wave damping model based on a prediction of current- and wave-induced force on individual plants. The model captures the influence of reconfiguration on wave forces, the impact of current on wave group velocity, and the modification of in-canopy time-mean and wave orbital velocity associated with canopy drag, all of which affect the wave dissipation by vegetation. The model explains why weak current reduces wave dissipation while strong current increases wave dissipation, as observed both in the present and previous studies. Further, we explore the impact of plant flexibility and leaf morphology on wave dissipation over a wide range of current to wave velocity ratio.
      [Phys. Rev. Fluids 6, 100502] Published Wed Oct 13, 2021
      Keywords: Invited Articles
      Citation: Phys. Rev. Fluids 6, 100502 (2021)
      PubDate: 2021-10-13T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.100502
      Issue No: Vol. 6, No. 10 (2021)
       
  • Simple analytic model for peristaltic flow and mixing

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      Authors: Ruy Ibanez; Mohammad Shokrian, Jong-Hoon Nam, Douglas H. Kelley
      First page: 103101
      Abstract: Author(s): Ruy Ibanez, Mohammad Shokrian, Jong-Hoon Nam, and Douglas H. Kelley
      Small-amplitude peristaltic flows occur in many biological systems, and may occur in the inner ear. We present a simple analytic model for such flows, validated using simulations and measurements from a laboratory model of the inner ear. We demonstrate that Lagrangian transport dynamics can be reproduced accurately with our simple analytic model.
      [Phys. Rev. Fluids 6, 103101] Published Tue Oct 05, 2021
      Keywords: Biological and Biomedical Flows
      Citation: Phys. Rev. Fluids 6, 103101 (2021)
      PubDate: 2021-10-05T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103101
      Issue No: Vol. 6, No. 10 (2021)
       
  • Helical trajectories of swimming cells with a flexible flagellar hook

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      Authors: Zonghao Zou; Wilson Lough, Saverio Spagnolie
      First page: 103102
      Abstract: Author(s): Zonghao Zou, Wilson Lough, and Saverio Spagnolie
      A model bacterium with a flexible flagellar hook generically swims along a helical trajectory, even when incorporating detailed hydrodynamics. A bifurcation in the hook’s equilibrium bending angle below a critical bending stiffness can have a dramatic effect on the trajectory’s helical pitch angle. Analytical predictions for the bifurcation’s dependence on the hook’s spontaneous curvature, the shape of the cell body, and the flagellum geometry are provided.
      [Phys. Rev. Fluids 6, 103102] Published Mon Oct 11, 2021
      Keywords: Biological and Biomedical Flows
      Citation: Phys. Rev. Fluids 6, 103102 (2021)
      PubDate: 2021-10-11T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103102
      Issue No: Vol. 6, No. 10 (2021)
       
  • Fall and break-up of viscous miscible drops in a Hele-Shaw cell

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      Authors: Clément Toupoint; Sylvain Joubaud, Bruce R. Sutherland
      First page: 103601
      Abstract: Author(s): Clément Toupoint, Sylvain Joubaud, and Bruce R. Sutherland
      We study the fall of pancake-shaped drops in a Hele-Shaw cell filled with a more viscous ambient fluid in the case where the drop and ambient fluid are miscible. We propose a theoretical expression for the falling velocity of the drops which takes into account elongated drops with width smaller than the gap of the cell. We also provide experimental evidence for the break-up of miscible drops, which can be caused by internal fluid motion within the drop, or by an instability in the shape of the drop.
      [Phys. Rev. Fluids 6, 103601] Published Wed Oct 06, 2021
      Keywords: Drops, Bubbles, Capsules, and Vesicles
      Citation: Phys. Rev. Fluids 6, 103601 (2021)
      PubDate: 2021-10-06T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103601
      Issue No: Vol. 6, No. 10 (2021)
       
  • Saturation mechanism of the fluctuation dynamo in supersonic turbulent
           plasmas

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      Authors: Amit Seta; Christoph Federrath
      First page: 103701
      Abstract: Author(s): Amit Seta and Christoph Federrath
      The physical mechanism of converting the kinetic energy of turbulence to magnetic energy is known as a dynamo. Fluctuation dynamo amplifies magnetic fields at scales smaller than the driving scale of turbulence. We show that the fluctuation dynamo in subsonic turbulent plasma is similar to the supersonic case in some aspects and very different in others.
      [Phys. Rev. Fluids 6, 103701] Published Mon Oct 04, 2021
      Keywords: Electrokinetic Phenomena, Electrohydrodynamics, and Magnetohydrodynamics
      Citation: Phys. Rev. Fluids 6, 103701 (2021)
      PubDate: 2021-10-04T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103701
      Issue No: Vol. 6, No. 10 (2021)
       
  • Dynamics of thin jets generated by temperature fronts

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      Authors: V. P. Goncharov
      First page: 103801
      Abstract: Author(s): V. P. Goncharov
      This manuscript presents a derivation of path equations to describe the dynamics of thin jets evolving along temperature fronts. The results show spiral-like solutions, as opposed to the case of jets arising at potential vorticity fronts.
      [Phys. Rev. Fluids 6, 103801] Published Fri Oct 01, 2021
      Keywords: Geophysical, Geological, Urban, and Ecological Flows
      Citation: Phys. Rev. Fluids 6, 103801 (2021)
      PubDate: 2021-10-01T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103801
      Issue No: Vol. 6, No. 10 (2021)
       
  • Predator-prey plankton dynamics in turbulent flow past an obstacle

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      Authors: Alice Jaccod; Stefano Berti, Enrico Calzavarini, Sergio Chibbaro
      First page: 103802
      Abstract: Author(s): Alice Jaccod, Stefano Berti, Enrico Calzavarini, and Sergio Chibbaro
      A predator-prey model of plankton dynamics in a turbulent flow past an idealized island is studied through fully-resolved numerical simulations to understand the complex interplay between biological excitable behavior and flow transport. We provide evidence that for a certain relation between advective and biological time scales, plankton accumulates in localized filamentary regions where velocity gradients compete with reaction-diffusion spreading, favoring persistence and primary production. The impact of small turbulent scales and of the geometrical details of the obstacle are investigated as well, quantifying their effects on plankton dynamics and patchiness.
      [Phys. Rev. Fluids 6, 103802] Published Mon Oct 04, 2021
      Keywords: Geophysical, Geological, Urban, and Ecological Flows
      Citation: Phys. Rev. Fluids 6, 103802 (2021)
      PubDate: 2021-10-04T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103802
      Issue No: Vol. 6, No. 10 (2021)
       
  • Effects of spanwise confinement on stratified shear instabilities

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      Authors: Yves-Marie Ducimetière; François Gallaire, Adrien Lefauve, Colm-cille P. Caulfield
      First page: 103901
      Abstract: Author(s): Yves-Marie Ducimetière, François Gallaire, Adrien Lefauve, and Colm-cille P. Caulfield
      We study the influence of transverse confinement on the linear instability properties of velocity and density distributions evoking exchange flows in stratified inclined ducts. In the chosen parameter space, we find that the presence of lateral walls has a stabilizing effect. The growth-rate predictions for the spanwise-invariant cases are almost systematically an upper bound to the growth-rate corresponding to the confined geometry. In addition, accounting for spanwise-varying perturbations result in the proliferation of unstable modes that present an odd-even regularity in their spatial structures, which is rationalized by comparison to the dispersion relation obtained for oblique waves.
      [Phys. Rev. Fluids 6, 103901] Published Mon Oct 11, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 103901 (2021)
      PubDate: 2021-10-11T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103901
      Issue No: Vol. 6, No. 10 (2021)
       
  • Bifurcations of a plane parallel flow with Kolmogorov forcing

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      Authors: Kannabiran Seshasayanan; Vassilios Dallas, Stephan Fauve
      First page: 103902
      Abstract: Author(s): Kannabiran Seshasayanan, Vassilios Dallas, and Stephan Fauve
      We study the primary bifurcations of a plane parallel flow in a channel with Kolmogorov forcing. We find a new type of bifurcation with both the oscillation frequency and the amplitude of the growing mode being zero at the threshold. We call this a stationary drift bifurcation. The laminar steady flow can display different types of bifurcation depending on the forcing wave number of the base flow. This is in contrast to the case of doubly periodic boundary conditions for which the primary bifurcation is stationary.
      [Phys. Rev. Fluids 6, 103902] Published Thu Oct 14, 2021
      Keywords: Instability, Transition, and Control
      Citation: Phys. Rev. Fluids 6, 103902 (2021)
      PubDate: 2021-10-14T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.103902
      Issue No: Vol. 6, No. 10 (2021)
       
  • Contribution of Mach number to the evolution of the Richtmyer-Meshkov
           instability induced by a shock-accelerated square light bubble

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      Authors: Satyvir Singh
      First page: 104001
      Abstract: Author(s): Satyvir Singh
      The Richtmyer-Meshkov (RM) instability has long been an interesting subject due to its fundamental significance in scientific research. In the current study, the contribution of shock Mach number on the evolution of the RM instability induced by a shock-accelerated square light bubble is investigated numerically. The shock Mach number causes significant changes in flow morphology, resulting in complex wave patterns, vorticity generation, vortex formation, and bubble deformation. The Mach number effects are explored in detail through various physical phenomena such as vorticity production, kinetic energy, dissipation rate, and enstrophy.
      [Phys. Rev. Fluids 6, 104001] Published Mon Oct 04, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 104001 (2021)
      PubDate: 2021-10-04T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104001
      Issue No: Vol. 6, No. 10 (2021)
       
  • Asymmetric coalescence of two droplets with different surface tensions is
           caused by capillary waves

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      Authors: Michiel A. Hack; Patrick Vondeling, Menno Cornelissen, Detlef Lohse, Jacco H. Snoeijer, Christian Diddens, Tim Segers
      First page: 104002
      Abstract: Author(s): Michiel A. Hack, Patrick Vondeling, Menno Cornelissen, Detlef Lohse, Jacco H. Snoeijer, Christian Diddens, and Tim Segers
      When two droplets with different surface tensions collide, the shape evolution of the merging droplets is asymmetric. Here, we reveal the importance of capillary waves in this process, and systematically study the influence of both inertia and surface tension. Counterintuitively, the Marangoni effect reduces the asymmetry.
      [Phys. Rev. Fluids 6, 104002] Published Tue Oct 05, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 104002 (2021)
      PubDate: 2021-10-05T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104002
      Issue No: Vol. 6, No. 10 (2021)
       
  • Rivulet flow over and through a permeable membrane

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      Authors: Abdulwahed S. Alshaikhi; Stephen K. Wilson, Brian R. Duffy
      First page: 104003
      Abstract: Author(s): Abdulwahed S. Alshaikhi, Stephen K. Wilson, and Brian R. Duffy
      Motivated by small-scale natural and industrial processes involving flow over and/or through a layer of a porous medium, a mathematical model for the steady gravity-driven flow of a slowly varying and thin rivulet of fluid over and through an even thinner permeable membrane is formulated and analyzed. The three-dimensional shape of the free surface of a rivulet with either fixed semi-width or fixed contact angle is determined, and it is shown how the length, base area and volume of the rivulet on the permeable part of the membrane depend on the physical properties of the system.
      [Phys. Rev. Fluids 6, 104003] Published Thu Oct 07, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 104003 (2021)
      PubDate: 2021-10-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104003
      Issue No: Vol. 6, No. 10 (2021)
       
  • Stability of similarity solutions of viscous thread pinch-off

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      Authors: Michael C. Dallaston; Chengxi Zhao, James E. Sprittles, Jens Eggers
      First page: 104004
      Abstract: Author(s): Michael C. Dallaston, Chengxi Zhao, James E. Sprittles, and Jens Eggers
      We show for the first time that only one similarity solution that describes the break-up of viscous liquid threads is linearly stable, while other similarity solutions are unstable. Complex eigenvalues lead to the presence of oscillations close to the break-up.
      [Phys. Rev. Fluids 6, 104004] Published Fri Oct 08, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 104004 (2021)
      PubDate: 2021-10-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104004
      Issue No: Vol. 6, No. 10 (2021)
       
  • Impact of viscosity ratio on falling two-layer viscous film flow inside a
           tube

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      Authors: H. Reed Ogrosky
      First page: 104005
      Abstract: Author(s): H. Reed Ogrosky
      A two-layer falling film consisting of two viscous fluids with identical density but different viscosity lining the interior of a vertical tube is studied using a long-wave asymptotic model. The impact of the viscosity ratio on the film linear stability and nonlinear dynamics are explored. It is shown that a less viscous outer layer can decrease the total film thickness required for plugs to form; the significance of this study for applications, including human airways, is briefly discussed.
      [Phys. Rev. Fluids 6, 104005] Published Wed Oct 13, 2021
      Keywords: Interfacial Phenomena and Flows
      Citation: Phys. Rev. Fluids 6, 104005 (2021)
      PubDate: 2021-10-13T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104005
      Issue No: Vol. 6, No. 10 (2021)
       
  • Role of caking in optimizing the performance of a concertinaed ceramic
           filtration membrane

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      Authors: V. E. Pereira; M. P. Dalwadi, I. M. Griffiths
      First page: 104301
      Abstract: Author(s): V. E. Pereira, M. P. Dalwadi, and I. M. Griffiths
      A study of caking in a concertinaed filtration membrane uncovers potential inaccuracies in using flux–throughput curves to determine filter-blocking behavior, and further explores the effect of membrane properties and configuration on flow and blocking dynamics.
      [Phys. Rev. Fluids 6, 104301] Published Fri Oct 01, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 104301 (2021)
      PubDate: 2021-10-01T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104301
      Issue No: Vol. 6, No. 10 (2021)
       
  • Polymer drag reduction in surfactant-contaminated turbulent bubbly channel
           flows

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      Authors: Daulet Izbassarov; Zaheer Ahmed, Pedro Costa, Ville Vuorinen, Outi Tammisola, Metin Muradoglu
      First page: 104302
      Abstract: Author(s): Daulet Izbassarov, Zaheer Ahmed, Pedro Costa, Ville Vuorinen, Outi Tammisola, and Metin Muradoglu
      Interface-resolved direct numerical simulations are performed to investigate the effects of clean (top) and contaminated (bottom) bubbles driven upward in Newtonian and viscoelastic turbulent channel flows. It is found that the viscoelasticity promotes formation of the bubble-wall layers and thus the polymer drag reduction is completely lost for the surfactant-free bubbly flows. An addition of a minute amount of Triton X-100 to the viscoelastic turbulent bubbly flow system is found to be sufficient to revive the polymer drag reduction effects.
      [Phys. Rev. Fluids 6, 104302] Published Mon Oct 04, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 104302 (2021)
      PubDate: 2021-10-04T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104302
      Issue No: Vol. 6, No. 10 (2021)
       
  • Preferential concentration by mechanically driven turbulence in the
           two-fluid formalism

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      Authors: Sara Nasab; Pascale Garaud
      First page: 104303
      Abstract: Author(s): Sara Nasab and Pascale Garaud
      Direct Numerical Simulations are employed to investigate preferential concentration of heavy inertial particles in a system in which turbulence is mechanically-driven. Using the two-fluid equations, we study this process and the resulting particle concentration enhancement for particles with St≲O(0.01). The results are similar to those found in previous work, where we established scaling laws to predict maximum and typical particle concentration enhancements in the context of the particle-driven convective instability.
      [Phys. Rev. Fluids 6, 104303] Published Fri Oct 08, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 104303 (2021)
      PubDate: 2021-10-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104303
      Issue No: Vol. 6, No. 10 (2021)
       
  • Granular avalanches of entangled rigid particles

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      Authors: Damien P. Huet; Maziyar Jalaal, Rick van Beek, Devaraj van der Meer, Anthony Wachs
      First page: 104304
      Abstract: Author(s): Damien P. Huet, Maziyar Jalaal, Rick van Beek, Devaraj van der Meer, and Anthony Wachs
      We explore the behavior of granular avalanches of nonconvex cross-shaped particles as a step forward in the modeling of entangled granular media. We conduct experiments and simulations of a dam break setup and report several flow regimes such as the top-driven collapse and the intermittent regime, in which the granular column sometimes remains stable and the flow outcome is determined by the random initial microstructure.
      [Phys. Rev. Fluids 6, 104304] Published Fri Oct 08, 2021
      Keywords: Multiphase, Granular, and Particle-Laden Flows
      Citation: Phys. Rev. Fluids 6, 104304 (2021)
      PubDate: 2021-10-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104304
      Issue No: Vol. 6, No. 10 (2021)
       
  • Coherent structures associated with interscale energy transfer in
           turbulent channel flows

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      Authors: Hongping Wang; Zixuan Yang, Ting Wu, Shizhao Wang
      First page: 104601
      Abstract: Author(s): Hongping Wang, Zixuan Yang, Ting Wu, and Shizhao Wang
      The flow fields of direct numerical simulation of turbulent channel flow are decomposed into large scales and small scales based on the interscale energy transfer spectra. The former is characterized by streaks and quasi-streamwise vortices even in the outer layer, and the latter is characterized by hairpin-like vortical structures that are similar to the original flow fields. We further investigated the coherent structures associated with the real-space energy transfer. The formation of small-scale hairpin-like vortices is related to the large-scale shear layer.
      [Phys. Rev. Fluids 6, 104601] Published Thu Oct 07, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 104601 (2021)
      PubDate: 2021-10-07T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104601
      Issue No: Vol. 6, No. 10 (2021)
       
  • Nonequilibrium turbulent dissipation in buoyant axisymmetric plume

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      Authors: Sunita; G. C. Layek
      First page: 104602
      Abstract: Author(s): Sunita and G. C. Layek
      This paper established the existence of non-Kolmogorov turbulence in free shear flows. The authors propose a set of dissipation laws and link them with the spreading rates as well as the entrainment coefficient, which varies with the rise of the plume in contrast to the Kolmogorov case. The work also show how the parameters of two stretching transformations determine both Kolmogorov and non-Kolmogorov turbulence.
      [Phys. Rev. Fluids 6, 104602] Published Fri Oct 08, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 104602 (2021)
      PubDate: 2021-10-08T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104602
      Issue No: Vol. 6, No. 10 (2021)
       
  • Hessian-based Lagrangian closure theory for passive scalar turbulence

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      Authors: Taketo Ariki; Kyo Yoshida
      First page: 104603
      Abstract: Author(s): Taketo Ariki and Kyo Yoshida
      A self-consistent closure theory of the passive scalar turbulence has been developed on the basis of the Hessian of the scalar field, where the characteristic timescale of the scalar is properly incorporated via Lagrangian time-advancement of the Hessian. Without relying on any empirical parameter, the theory reasonably predicts the Obukhov-Corrsin spectrum of the inertial-convective range with its universal constant.
      [Phys. Rev. Fluids 6, 104603] Published Mon Oct 11, 2021
      Keywords: Turbulent Flows
      Citation: Phys. Rev. Fluids 6, 104603 (2021)
      PubDate: 2021-10-11T10:00:00+00:00
      DOI: 10.1103/PhysRevFluids.6.104603
      Issue No: Vol. 6, No. 10 (2021)
       
 
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