Latest papers in fluid mechanics
Prediction of the reaction yield in a X-micromixer given the mixing degree and the kinetic constant
Author(s): S. Tomasi Masoni, A. Mariotti, M. Antognoli, C. Galletti, R. Mauri, M. V. Salvetti, and E. Brunazzi
Understanding flow regimes and mixing in microreactors is crucial for achieving high reaction yields. This study combines simulations and experiments in an X-microreactor up to Reynolds number (Re) 600. For Re > 375, an unsteady periodic regime is observed with a collapsing central vortical structure and symmetric vorticity shedding. Counterrotating vortices form, merge, and recreate the central vortex. Despite increased mixing in this regime, reaction yield remains similar due to reduced reactant residence time. A model predicting reaction yield based on mixing degree and nominal kinetic constant is developed, successfully encompassing all flow regimes and Damköhler numbers (0.1 < Da < 103).
[Phys. Rev. Fluids 9, 024202] Published Thu Feb 15, 2024
Validation of symmetry-induced high moment velocity and temperature scaling laws in a turbulent channel flow
Author(s): Francisco Alcántara-Ávila, Luis Miguel García-Raffi, Sergio Hoyas, and Martin Oberlack
The symmetry-based turbulence theory has been used to derive new scaling laws for the streamwise velocity and temperature moments of arbitrary order. For this, it has been applied to an incompressible turbulent channel flow driven by a pressure gradient with a passive scalar equation coupled in. To …
[Phys. Rev. E 109, 025104] Published Wed Feb 14, 2024
Stochastic reorientations and the hydrodynamics of microswimmers near deformable interfaces
Author(s): Sankalp Nambiar and J. S. Wettlaufer
We study the fluid mediated hydrodynamics of an orientable microscopic swimmer that is near a deformable boundary, and that can intrinsically execute random orientation changes. Accounting for swimmer reorientations via orientation tumbles or active Brownian rotations on time scales comparable to the boundary deformations, we find that a pusher-type swimmer can rotate away from the interface, while its attraction towards the interface is enhanced. Depending on the viscosity of the fluids on either side of the interface, the swimmer can experience a stronger migration towards the interface at short times, and away from the interface in the long-time limit.
[Phys. Rev. Fluids 9, 023102] Published Wed Feb 14, 2024
Arresting of interfacial phase separation with an imposed flow
Author(s): Ryuta X. Suzuki, Shoji Seya, Takahiko Ban, Manoranjan Mishra, and Yuichiro Nagatsu
We experimentally investigate displacement of a more viscous liquid by a less viscous one in a Hele-Shaw cell using an aqueous two phase system, where phase separation occurs in the growing liquid-liquid interfacial region, by varying the injection flow rate and the phase separation rate. We show that the degree of the interfacial phase separation scales as a unique function of the ratio of the flow and phase separation rates and it decreases with the ratio. These results demonstrate that the interfacial phase separation is arrested by the imposed flow and determined by competition between the flow and phase separation rates. The arresting effect and the mechanism are numerically verified.
[Phys. Rev. Fluids 9, 024003] Published Wed Feb 14, 2024
Experimental and numerical investigation of three-dimensional shock train topology with differently oriented background waves
Author(s): Dayi Wang, Ziao Wang, Juntao Chang, Lianjie Yue, Gang Wang, and Hao Chen
To better understand the three-dimensional topology of the interaction between the shock train and the background wave, the steady and dynamic characteristics of a shock train were investigated using wind-tunnel experiments and numerical simulation. A 14° wedge placed at the bottom and sidewalls was…
[Phys. Rev. E 109, 025103] Published Tue Feb 13, 2024
Effects of symmetry-breaking mechanisms on the flow field around magnetic-responsive material appendages that mimic swimming strokes
Author(s): Mohammad Mohaghar, Angelica A. Connor, Shuai Wu, Ruike Renee Zhao, and Donald R. Webster
This study quantifies the effects of breaking the symmetry of magnetic-responsive material appendage motion. Asymmetry is achieved through distinct shape changes and asymmetric cycle periods. The appendage with an asymmetric joint and asymmetric cycle demonstrates significantly faster downward motion (and enhances swimming efficiency) by reducing the vorticity strength and viscous energy dissipation in the surrounding fluid. The study provides insights into the induced flow and opens avenues for bio-inspired aquatic robots made from magnetic-responsive soft materials with the potential for fostering underwater propulsion and exploration in aquatic environments.
[Phys. Rev. Fluids 9, 023101] Published Tue Feb 13, 2024
Electrophoretic maneuvering of nonuniformly charged particles suspended in linear flows: Impact of the medium viscoelasticity
Author(s): Rajnandan Borthakur and Uddipta Ghosh
Electrophoresis often coexists with imposed background flows in many applications. When particles carry nonuniform surface charge, and the fluid itself is complex, the particles may follow fascinating trajectories, as shown in this work. Indeed, the combined action of a background flow and complex fluidic medium may cause particles to undergo cross-stream migration. However, the very nature of its trajectory and the extent of its migration depends on whether the imposed flow or the electrophoretic propulsion dominates the motion. The insights provided here may be exploited for improving electrophoretic separation and sorting of particles based on their size and surface charge.
[Phys. Rev. Fluids 9, 023302] Published Tue Feb 13, 2024
Flow of a shear-thinning fluid in a rectangular duct
Author(s): Ilya Barmak, Davide Picchi, Alexander Gelfgat, and Neima Brauner
A rigorous numerical solution for steady laminar flows of shear-thinning fluids in rectangular ducts is presented for the first time. We derive universal scaling laws for the effective viscosity that depends on the dimensionless rheological parameters and the effective channel size that is a function of the aspect ratio of the duct. These allow us to generalize the classical formula for the friction factor of Newtonian flows (12/Re) to Carreau fluids flowing in rectangular ducts of any aspect ratio, where the Reynolds number is based on the effective channel size and the effective viscosity.
[Phys. Rev. Fluids 9, 023303] Published Tue Feb 13, 2024
Thermal boundary layers in turbulent Rayleigh-Bénard convection with rough and smooth plates: A one-to-one comparison
Author(s): Ronald du Puits
Roughness at a surface hotter or colder than its environment may significantly enhance the convective heat transfer coefficient. This enhancement results from modification of the near-wall flow field. Our work demonstrates how roughness elements deform the temperature field compared to a smooth surface, and, under which conditions the heat transfer coefficient is enhanced.
[Phys. Rev. Fluids 9, 023501] Published Tue Feb 13, 2024
Stability of traveling waves of a thermoviscous liquid film down the outer surface of a cylinder
Author(s): Garima Singh and Naveen Tiwari
The stability of a traveling wave on the outside of a heated solid vertical cylinder is considered. The axisymmetric traveling wave becomes unstable and leads to the formation of asymmetric droplets over the cylinder. Eigenvalue analysis indicates that at smaller wavenumbers, the gravity mode exists, and a thermocapillary mode also exists but at larger wavenumbers. Patterns generated using nonlinear analysis show that the selected mode is governed by the geometric confinement in the azimuthal direction. Interesting nonlinear patterns are obtained due to an interesting interplay between the gravity mode and thermocapillary mode.
[Phys. Rev. Fluids 9, 024002] Published Tue Feb 13, 2024
Turbulent power theory in heavy-ion plasma of a Jovian magnetosphere
Author(s): Vitaliy Kaminker
Turbulent power is introduced in to Jupiter’s magnetosphere near the cen- trifugal equator of the plasma disc. Turbulent fluctuations are generated within the plasma fluid. Turbulent energy then travels out of the plasma disc via shear Alfvén waves, dissipating out of the system along the way.
[Phys. Rev. Fluids 9, 024602] Published Tue Feb 13, 2024
Shear-triggered coalescence
Author(s): Alireza Mashayekhi, Coralie Vazquez, Hongying Zhao, Michael Gattrell, James F. Gilchrist, and John M. Frostad
In prior work, it was observed that some bitumen droplets coalesced faster when colliding in shear than colliding head-on. Inspired by this observation, we aimed to reproduce the same behavior in a simpler system composed of pure oil, water, and surfactants/particles. Using a cantilevered-capillary force apparatus we observed this phenomenon for droplets stabilized by cellulose nanocrystals and coined the term “shear-triggered coalescence” to describe it.
[Phys. Rev. Fluids 9, 023602] Published Thu Feb 08, 2024
Instability and rupture of sheared viscous liquid nanofilms
Author(s): Vira Dhaliwal, Christian Pedersen, Kheireddin Kadri, Guillaume Miquelard-Garnier, Cyrille Sollogoub, Jorge Peixinho, Thomas Salez, and Andreas Carlson
Liquid nanofilms are subject to rupture due to intermolecular forces triggered by surface perturbations arising from thermal fluctuations. When a shear stress is imposed at the free surface it becomes stable in the direction of shear, but perturbations can still grow in the perpendicular direction to the shear.
[Phys. Rev. Fluids 9, 024201] Published Thu Feb 08, 2024
Turbulent puffs in transitional pulsatile pipe flow at moderate pulsation amplitudes
Author(s): Daniel Morón and Marc Avila
Pulsatile pipe flow, or the flow in a pipe with a mean and one or more harmonic bulk velocity components, is a benchmark to study unsteady driven flows in industrial and biological applications. We study the transitional regime of pulsatile pipe flow at moderate-to-high amplitudes and intermediate pulsation frequencies. We show that, as in steady driven pipe flow, the first long-lived turbulent structures are localized. We combine direct numerical simulations, causal analysis and turbulence modeling to describe the behavior of these turbulent patches in pulsatile pipe flow, and to determine the physical mechanisms by which they survive the pulsation.
[Phys. Rev. Fluids 9, 024601] Published Thu Feb 08, 2024
Laser-induced thermocapillary flows on a flowing soap film
Author(s): Yu Zhao and Haitao Xu
We propose a focused laser heating method to study wave properties of flowing soap films. The laser-induced thermocapillary flows lead to symmetric disturbances in film thickness. The shock waves originating from the propagating symmetric elastic waves, which have remained elusive despite considerable experimental efforts, are thus stimulated on flowing soap films with low surfactant concentrations, or appreciable elasticities. Interestingly, on soap films with high surfactant concentrations, or vanishingly small elasticities, the laser-induced disturbances in film thickness remain unchanged and flow with the film without propagating, creating “laser-engraving” on free liquid films.
[Phys. Rev. Fluids 9, L022001] Published Thu Feb 08, 2024
Electrowetting dynamics of sessile droplets in a viscous medium
Author(s): Juan S. Marin Quintero, Butunath Majhy, and Prashant R. Waghmare
This work analyzes the transient wetting dynamics of droplets in viscous media with appropriate governing parameters and examines the drop’s transient response immediately after the actuation, the drop’s retraction and resultant dynamics, and the effect of multiple wave actuation on the droplet transition.
[Phys. Rev. Fluids 9, 024001] Published Wed Feb 07, 2024
Reversal of the transverse force on a spherical bubble rising close to a vertical wall at moderate-to-high Reynolds numbers
Author(s): Pengyu Shi
Bubbles rising near a vertical wall are known to bounce repeatedly when the Reynolds number (Re) exceeds about 65. This behavior contradicts potential flow theory, which suggests a consistently attractive transverse force. In this study, we demonstrate through numerical simulations that below a critical Re-dependent separation, the transverse force decreases with decreasing separation, potentially reversing from attractive to repulsive. We believe this reversal is responsible for the bouncing motion observed in freely near-wall rising bubbles.
[Phys. Rev. Fluids 9, 023601] Published Tue Feb 06, 2024
Near-critical behavior of the Zhong-Zhang model
Author(s): J. H. Lowenstein
The Zhong-Zhang (ZZ) model is a one-degree-of-freedom dynamical system describing the motion of an insulating plate of length d floating on the upper surface of a convecting fluid, with locking at the boundaries. In the absence of noise, the system away from the boundaries is described by linear dif…
[Phys. Rev. E 109, 025102] Published Mon Feb 05, 2024
Electroosmotic mixing of viscoplastic fluids in a microchannel
Author(s): Sumit Kumar Mehta and Pranab Kumar Mondal
This work finds that the yield stress (YS) of electrically actuated viscoplastic fluids significantly influences mixing and aggregation phenomena. When shear force is applied below the YS limit, these fluids exhibit solid-like behavior due to their viscoplasticity. This is commonly observed in biological fluids like blood used in applications where rapid mixing is crucial. The local modulation of electrical forcing is achievable due to the ionic interaction between the solid and liquid phases. This leads to the observation of distinct flow structures, found to be influenced by the YS. Additionally, the likelihood of constituent particles aggregating is strongly correlated with YS.
[Phys. Rev. Fluids 9, 023301] Published Mon Feb 05, 2024
Data-based approach for time-correlated closures of turbulence models
Author(s): J. Domingues Lemos and A. A. Mailybaev
Developed turbulent motion of fluid still lacks an analytical description despite more than a century of active research. Nowadays, phenomenological ideas are widely used in practical applications, such as small-scale closures for numerical simulations of turbulent flows. In the present paper, we us…
[Phys. Rev. E 109, 025101] Published Thu Feb 01, 2024