Physical Review Fluids

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Updated: 23 hours 44 min ago

Linear stability of ultrathin spherical coatings

Wed, 01/24/2024 - 10:00

Author(s): D. Moreno-Boza and A. Sevilla

This work investigates the linear stability of an ultrathin non-wetting liquid film on a spherical substrate in the limit of negligible inertia. The interplay between destabilizing van der Waals forces, with an exact potential description, and stabilizing surface tension gives rise to a discrete set of unstable temporal modes. Also, the performance of classical lubrication models has been assessed against the complete Stokes equations of motion.


[Phys. Rev. Fluids 9, 014004] Published Wed Jan 24, 2024

Koopman-based model predictive control with morphing surface: Regulating the flutter response of a foil with an active flap

Wed, 01/24/2024 - 10:00

Author(s): Tso-Kang Wang and Kourosh Shoele

In this work, we demonstrated how model predictive control (MPC) can effectively manipulate a highly nonlinear foil-and-flap system to follow designated lift trajectories to sub-5% error. The surrogate model is built through a data-driven method merging fluidic and structural information which can be readily deployed to numerous fluid-structure interaction systems. The rapid optimization procedure utilized to generate the control signal can also be used for estimating ambient environmental change


[Phys. Rev. Fluids 9, 014702] Published Wed Jan 24, 2024

Quantifying and predicting near-wall global intermittency in stably stratified channel flow

Wed, 01/24/2024 - 10:00

Author(s): Haoyang Cen, Artem Korobenko, and Qi Zhou

In this study, we explore the transition from fully developed turbulence to global intermittency in stably stratified channel flow using direct numerical simulations across varying friction Reynolds and shear Richardson numbers. We quantify intermittency by measuring the volume fraction of turbulent patches and find that intermittency can originate from either near-wall or mid-channel regions, depending on the above parameters. The study identifies a critical value of the Nusselt number (approximately 3.0) below which near-wall intermittency consistently occurs. The critical friction Richardson number for intermittency is found to be proportional to the squared Reynolds number.


[Phys. Rev. Fluids 9, 014803] Published Wed Jan 24, 2024

Cavity dynamics and vibrations of a flexible hydrofoil in the cavitating flow

Tue, 01/23/2024 - 10:00

Author(s): Yunqing Liu, Qin Wu, Hanzhe Zhang, and Biao Huang

This work reveals the mechanism of cavitation-structure interaction by comparing experimental results between a stainless-steel hydrofoil and a flexible hydrofoil, encompassing hydrodynamic loads, cavitation structures, vibrations, and deformations. The hydrodynamic load induces nose-up twisting deformation, which subsequently increases the angle of attack, promoting cavitation inception. Additionally, the dynamics of cloud cavities induced by the shock wave mechanism are clarified based on high-speed images.


[Phys. Rev. Fluids 9, 014304] Published Tue Jan 23, 2024

Space-local Navier–Stokes turbulence

Tue, 01/23/2024 - 10:00

Author(s): Ryo Araki, Wouter J. T. Bos, and Susumu Goto

How local is turbulence? This question has been extensively examined in scale space. In this study, we investigate the locality in physical space by artificially truncating the spatially nonlocal nonlinear interactions and see how the energy cascade is affected by the truncation in three-dimensional turbulence.


[Phys. Rev. Fluids 9, 014603] Published Tue Jan 23, 2024

Self-organization of autophoretic suspensions in confined shear flows

Mon, 01/22/2024 - 10:00

Author(s): Prathmesh Vinze and Sebastien Michelin

Phoretic particles swim and interact exploiting their dual chemical and hydrodynamic footprint on their environment, resulting in complex collective behavior spontaneously but also in response to external forcing. Here, based on a kinetic model for dilute suspensions, we numerically characterize their response to shear in a confined environment and identify three different regimes depending on the relative magnitude of shear forcing, chemotaxis, self-propulsion and confinement. The particles, in turn, exert microscopic stresses on their surroundings, resulting in a complex rheological response tightly linked to the self-organization regime.


[Phys. Rev. Fluids 9, 014202] Published Mon Jan 22, 2024

Low-order planar pressure reconstruction of stalled airfoils using particle image velocimetry data

Fri, 01/19/2024 - 10:00

Author(s): D. W. Carter and B. Ganapathisubramani

Structures in turbulent flow are largely responsible for variations in the forces experienced by the body of interest. In this work, the impact of specific structures in the velocity field on the resulting pressure field are revealed using a data-driven framework. The body of interest is a stalled NACA 0012 airfoil obtained from high-resolution large-scale time-resolved particle image velocimetry.


[Phys. Rev. Fluids 9, 014602] Published Fri Jan 19, 2024

Conformations, correlations, and instabilities of a flexible fiber in an active fluid

Thu, 01/18/2024 - 10:00

Author(s): Scott Weady, David B. Stein, Alexandra Zidovska, and Michael J. Shelley

Many biological systems rely on interactions between active processes and passive, deformable structures to properly function. An important example is chromatin in the cell nucleus, where ATP-powered processes, such as transcription or DNA repair, act on the chromatin fiber and influence its motion. Motivated by this system, in this study we develop and analyze a model of a flexible fiber in an active suspension as an analog to a chromatin fiber in an active environment - the nucleoplasm. Interactions between the suspension and the fiber lead to a novel bend instability, and nonlinear simulations identify coherent motions and conformations of the fiber over long timescales.


[Phys. Rev. Fluids 9, 013102] Published Thu Jan 18, 2024

Activity-induced asymmetric dispersion in confined channels with constriction

Thu, 01/18/2024 - 10:00

Author(s): Armin Maleki, Malihe Ghodrat, and Ignacio Pagonabarraga

Our Brownian dynamics model uncovers response mechanisms of microorganisms such as Escherichia coli to shear flows and constrictions, shedding light on anomalous accumulation of active particles in confined channels. Our findings highlight the butterfly-like attractors that trap particles past the constriction and characterize relevant dynamical regimes of active particle accumulation. We also explore the impact of particle size, channel geometry, and fluid velocity on trapping probability and accumulation strength. This intriguing phenomenon could be utilized as geometrical sift for mixture of active particles with different sizes/velocities and lead to innovations in particle manipulation.


[Phys. Rev. Fluids 9, 013103] Published Thu Jan 18, 2024

Onset of Lagrangian chaos: From fractal power spectrum to the absolutely continuous one

Thu, 01/18/2024 - 10:00

Author(s): Rafil V. Sagitov, Igor I. Wertgeim, and Michael A. Zaks

We study fluid motions excited by a spatially periodic force in a plane region with periodic boundary conditions; mean drift in both directions across the domain is nonzero. Under weak force, the flow is stationary; Fourier spectra of velocity for advected tracer particles are singular continuous (fractal). At higher amplitudes of the force, the flow pattern periodically oscillates, ensuring the onset of Lagrangian chaos in tracer dynamics. We illustrate the transformation of the power spectrum from the fractal object to the conventional smooth curve (subplots (i-iv)), and describe the accompanying changes in the pattern of autocorrelation for the tracer velocity.


[Phys. Rev. Fluids 9, 014401] Published Thu Jan 18, 2024

Role of vorticity distribution in the rise and fall of lift during a transverse gust encounter

Thu, 01/18/2024 - 10:00

Author(s): Antonios Gementzopoulos, Girguis Sedky, and Anya Jones

In this paper, we experimentally investigate the flow fields and lift transients associated with transverse gust encounters. We highlight the key differences between inviscid and viscous gust encounters and discuss how contrasting shed vorticity distributions lead to dissimilar lift behavior during the gust exit. Our findings contribute to a refined understanding of the utility of inviscid models in the prediction of loads during atmospheric gust encounters.


[Phys. Rev. Fluids 9, 014701] Published Thu Jan 18, 2024

Absolute and convective instability of a round jet emerging into an ambient medium of different viscosity

Wed, 01/17/2024 - 10:00

Author(s): Jinwei Yang and Vinod Srinivasan

The case of a round jet of one liquid emerging into an ambient medium of a different viscosity is relevant to many industrial mixing situations. A linear spatiotemporal analysis of such a configuration shows that for sufficiently high viscosity contrast, the flow is absolutely unstable. Both axisymmetric and helical modes are unstable, with the axisymmetric mode being slightly dominant. The absolute/convective instability transition boundary defined in terms of viscosity ratio and jet Reynolds number is compared to the results of recent experiments and good agreement is found.


[Phys. Rev. Fluids 9, 013903] Published Wed Jan 17, 2024

Pore-corner networks unveiled: Extraction and interactions in porous media

Wed, 01/17/2024 - 10:00

Author(s): Ninghua Zhan, Yiping Wang, Xiang Lu, Rui Wu, and Abdolreza Kharaghani

A novel pore-corner network extraction method is proposed. To validate our proposed extraction method, a generalized network model is developed to simulate evaporation in a porous medium composed of packed spherical beads. The modeling results are in good agreement with the experimental data, particularly in terms of the variation of liquid distribution over time. Our proposed extraction method not only contributes to disclose the structures of pores and corners in real porous media but also benefits the development of generalized network models that can be employed to understand in detail the multiphase transport in porous media from the pore scale perspective.


[Phys. Rev. Fluids 9, 014303] Published Wed Jan 17, 2024

Level crossings reveal organized coherent structures in a turbulent time series

Wed, 01/17/2024 - 10:00

Author(s): Subharthi Chowdhuri and Tirtha Banerjee

Detection of coherent structures in experiments, when using single-point temporal measurements, poses challenges due to their three-dimensional nature. Past methods, relying on ad hoc thresholds, lacked consistency across studies. To address this, the level-crossing method has been introduced and applied to two datasets of wall-bounded turbulent flows. This method allows the identification of coherent structures in a more objective manner, avoiding the need for arbitrary thresholds. An interesting discovery is that coherent structures influence near-wall turbulence through nonlinear interactions, a phenomenon not discernible through traditional spectral analysis.


[Phys. Rev. Fluids 9, 014601] Published Wed Jan 17, 2024

Electro-poroelastohydrodynamics of the endothelial glycocalyx layer and streaming potential in wavy-wall microvessels

Tue, 01/16/2024 - 10:00

Author(s): C. Teodoro, J. Arcos, O. Bautista, and F. Méndez

The study of the endothelial glycocalyx layer (EGL) has been of great interest in recent years due to its direct relationship with human health. Some works have modeled the EGL under the triphasic mixture theory (TMT), considering an electrically charged porous medium interacting with the electrolyte under a pressure gradient. Our study is based on a model that couples the mechanical and electrical interaction, considering TMT, a non-Newtonian electrolyte, and wavy walls using the domain perturbation method, focusing on the shear stresses in the EGL and on the induced streaming potential that can be used as a biocompatible energy source.


[Phys. Rev. Fluids 9, 013101] Published Tue Jan 16, 2024

Onset of Rayleigh-Bénard convection in dielectric liquids with electric conduction

Tue, 01/16/2024 - 10:00

Author(s): Yuxing Peng, R. Deepak Selvakumar, and Jian Wu

The convective flow of dielectric liquids with finite electric conductivity subjected to the simultaneous action of an electric field and a destabilizing temperature gradient is investigated. The instability of the system is studied through modal stability analysis, and it is found that the onset of the flow is delayed when an electric field is applied. Numerical simulations are performed to show the flow patterns and heat transfer characteristics. The dual solutions are highlighted in the bifurcation diagram.


[Phys. Rev. Fluids 9, 013902] Published Tue Jan 16, 2024

Flow stability in shallow droplets subject to localized heating of the bottom plate

Tue, 01/16/2024 - 10:00

Author(s): Khang Ee Pang, Charles Cuvillier, Yutaku Kita, and Lennon Ó Náraigh

When the surface tension of a droplet or a film varies inhomogeneously, a surface-tension gradient occurs, which induces a flow inside the fluid. Thermocapillary flows induced by localized heating have been observed experimentally in millimeter-sized water droplets. In particular, these experiments reveal that when such droplets are heated from below by a localized heat source targeted at the droplet center, a twin vortex pair perpendicular to the substrate is observed. This work aims to obtain some theoretical understanding to explain the onset of such vortices.


[Phys. Rev. Fluids 9, 014003] Published Tue Jan 16, 2024

Spectral analysis for elastica dynamics in a shear flow

Tue, 01/16/2024 - 10:00

Author(s): Lujia Liu, Paweł Sznajder, and Maria L. Ekiel-Jeżewska

Equations are derived for the evolution of a three-dimensional perturbation of a straight slender elastic fiber at an arbitrary orientation in shear flow at low-Reynolds-number. For the orientation in the plane of the shear flow and the flow gradient, the spectral analysis is performed for in-plane and out-of-plane perturbations. The most unstable eigenfunctions and eigenvalues are analyzed and compared to the previous results for the in-plane perturbations in the shear flow, and for arbitrary perturbations in the compressional flow.


[Phys. Rev. Fluids 9, 014101] Published Tue Jan 16, 2024

Simple generalization of kinetic theory for granular flows of nonspherical, oriented particles

Tue, 01/16/2024 - 10:00

Author(s): Dalila Vescovi, Ben Nadler, and Diego Berzi

The collective motion of nonspherical particles displaying preferential alignment can be modeled by extending the kinetic theory of granular gases. A linear dependency on the orientational tensor into the constitutive relations for the stresses, and a balance law for the orientational tensor itself, in which a key role is played by the randomizing effect of collisions, permit to reproduce the discrete simulations of homogeneous shearing flows of cylinders at different aspect ratios.


[Phys. Rev. Fluids 9, L012301] Published Tue Jan 16, 2024

Dispersion and deformation of molecular patterns written in turbulent air

Fri, 01/12/2024 - 10:00

Author(s): Willem van de Water, Nico Dam, and Enrico Calzavarini

This letter “H” is written in turbulent air by tagging molecules in the focus of intense laser beams that cross in space. In the course of 40 microseconds, turbulence deforms and disperses the pattern. It could be used as a way to measure the velocity of the turbulent eddies. However, more importantly, it reveals the intricate interplay between molecular diffusion and turbulent dispersion.


[Phys. Rev. Fluids 9, 014502] Published Fri Jan 12, 2024

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