Latest papers in fluid mechanics

Author(s): Li Chen, Feng Wang, Yingrui Wang, Peng Huo, Yuqi Li, Xi Gu, Man Hu, and Daosheng Deng

The authors explore how solidification and thermo-instability could produce the sunflower shape of paraffin wax confined within a Hele-Shaw cell.

[Phys. Rev. Fluids 9, L072001] Published Mon Jul 01, 2024

Author(s): Sutapa Mandal, Snehashish Sarkar, and Pinaki Pal

The phenomenon of supercritical and subcritical transitions from one state to another with the variation of a control parameter is widely observed across a variety of natural as well as artificial systems. This paper investigates those transitions in the rotating Rayleigh-Bénard convection (RRBC) system. However, the complexity of RRBC so far hindered the simplest possible description of these transitions. Here, a very simple description of the phenomenon is presented using a pair of one dimensional reduced order models of the system in the presence of free-slip and no-slip boundary conditions. The results of the models are then validated with that of the direct numerical simulations.

[Phys. Rev. Fluids 9, 063503] Published Thu Jun 27, 2024

Author(s): Lichuan Xu, Adrian van Kan, Chang Liu, and Edgar Knobloch

We study turbulent fluctuation-induced transitions between hurricane-like large-scale vortices and unidirectional jets in stochastically forced, viscously damped two-dimensional turbulence within an elongated periodic domain. Using direct numerical simulations of unprecedented duration, lasting up to 10000 viscous time units, we collect detailed statistical data on the lifetimes of these metastable structures and quantify the impact of the domain aspect ratio, the forcing scale, and the Reynolds number. We also uncover irreversible transition paths between jets and vortices, which consist of two stages: a rapid change in structure and a subsequent slow viscous adjustment of kinetic energy.

[Phys. Rev. Fluids 9, 064605] Published Thu Jun 27, 2024

Author(s): A. Chauhan and C. Sasmal

We perform a comprehensive numerical study on all three modes of thermal convection (forced, free, and mixed) within a system comprising two concentric horizontal cylinders filled with viscoelastic fluids, with the inner cylinder rotating. In forced convection, the flow field remains stable, while in free and mixed convection, an increase in the Weissenberg number leads to a transition from steady to unsteady periodic, quasiperiodic, and finally, an aperiodic and chaotic behavior. This transition arises due to the presence of elastic instability and the subsequent appearance of elastic turbulence in viscoelastic fluids with the increasing Weissenberg number.

[Phys. Rev. Fluids 9, 063303] Published Tue Jun 25, 2024

Author(s): Junjie Li, Suofeng Han, Wenxue Han, Ronggang Wei, Chunbo Hu, and Chao Li

To study the effects of powder injection on hydrogen flame flow field parameters in scramjet, numerical simulation methods are employed. The study focuses on the influence of particle injection expansion angle and particle injection swirl on hydrogen flame flow field parameters. The computational results indicate that injecting powder fuel into the hydrogen flame leads to a decrease in flame flow field temperature.

[Phys. Rev. Fluids 9, 063201] Published Mon Jun 24, 2024

Author(s): Akhshay S. Bhadwal, Joseph R. L. Cousins, Nigel J. Mottram, Stephen K. Wilson, Brian R. Duffy, Ian C. Sage, and Carl V. Brown

We demonstrate control of the free surface profile of a rivulet of a nematic liquid crystal through the electric field-induced local increase of the effective viscosity of the rivulet. This resulting increase in rivulet height is studied experimentally, and is described theoretically in terms of the volume flux and the electric field strength. The localized effective viscosity change of the flow in this study occurs under isothermal conditions with the other physical properties of the liquid kept constant. The reported effect contrasts with temperature-dependent viscosity control techniques, which involve changes to the physical properties of the liquid.

[Phys. Rev. Fluids 9, 064002] Published Mon Jun 24, 2024

Author(s): Abbas Farhat, Pierre Philippe, Li-Hua Luu, Alexis Doghmane, and Pablo Cuéllar

Experiments based on hydraulic loading of artificial cemented granular layers by a localized upward water flow revealed the existence of three failure modes: (i) Overall block uplift; (ii) Block rupture by median crack at the inflow zone; (iii) Progressive excavation of a fluidized path along the walls. Despite these distinct scenarios driven by the boundary conditions, the critical flow values at breakpoint are consistent with each other, underlining the local character of the instability, and can be rationalized by extending Archimedes’ number to the present case involving adhesion between grains. Agreement is then established with the purely granular case.

[Phys. Rev. Fluids 9, 064305] Published Mon Jun 24, 2024

Author(s): Jonathan S. Van Doren and M. Houssem Kasbaoui

Inertial solid particles suspended in dense turbulent channels modulate turbulence and fluid mass flow rate through two mechanisms: (I) the increase of the suspension’s apparent kinematic viscosity with increasing solid volume fraction and (II) turbulence modulation through the particle feedback force. For particle volume fractions below 3%, the increase in suspensions apparent viscosity accounts for most of the modulation. As the volume fraction increases, the particle feedback force drives additional modulation beyond what the increased viscosity accounts for. Namely, this is a reduction in the bulk fluid velocity, reduction of turbulent fluctuations, and increased coefficient of friction.

[Phys. Rev. Fluids 9, 064306] Published Mon Jun 24, 2024

Author(s): Arslan Salim Dar and Fernando Porté-Agel

Most of the literature on flow over cliffs and its interaction with a wind turbine wake deals with wind direction perpendicular to the cliff. As wind direction can be oblique in reality, it is important to understand how the flow over a cliff can change with wind direction and what implications it can have for a wind turbine wake. In this study, we showed that above a certain wind direction, streamwise flow recirculation is replaced by a spanwise one, affecting flow shear and turbulence. In addition, we explored the complex interactions between flow over a cliff and a wind turbine wake, affecting its characteristics such as shape, recovery rate, and turbulence level in a nontrivial manner.

[Phys. Rev. Fluids 9, 064604] Published Mon Jun 24, 2024

Author(s): Arunava Das, Pinaki Dutta, and Vishwanath Shukla

We construct a formally time-reversible, one-dimensional forced Burgers equation by imposing a global constraint of energy conservation, wherein the constant viscosity is modified to a fluctuating state-dependent dissipation coefficient. The system exhibits dynamical properties which bear strong sim…

[Phys. Rev. E 109, 065108] Published Tue Jun 18, 2024

Author(s): Ting-Heng Hsieh, Wei-Chi Li, and Tzay-Ming Hong

When droplets approach a liquid surface, they have a tendency to merge in order to minimize surface energy. However, under certain conditions, they can exhibit a phenomenon called coalescence delay, where they remain separate for tens of milliseconds. This duration is known as the residence time or …

[Phys. Rev. E 109, 065109] Published Tue Jun 18, 2024

Author(s): B. Podvin, L. Soucasse, and F. Yvon

Natural convection motifs are identified in a Rayleigh-Bénard cubic cell using a probabilistic clustering method, Latent Dirichlet Allocation (LDA). The spatiotemporal features of the motifs at different Rayleigh numbers provide insight into the dynamics of the large-scale circulation (LSC), which is characterized by intermittent reorientations. A model based on the dominant heat flux motifs is found to predict successfully the average LSC reorientation rate, including in cases where few or even no reorientations are observed.

[Phys. Rev. Fluids 9, 063502] Published Tue Jun 18, 2024

Author(s): Marco Zecchetto, Ricardo P. Xavier, Miguel A. C. Teixeira, and Carlos B. da Silva

In turbulent free shear flows such as jets and wakes, and also in turbulent boundary layers, the turbulent region is bounded by a region of irrotational flow where the magnitude of the potential velocity fluctuations can be very high. This is particularly true close to the turbulent-nonturbulent int…

[Phys. Rev. E 109, 065107] Published Mon Jun 17, 2024

Author(s): Donovan J. M. Allum and Marek Stastna

Solar radiation is known to drive vertical motion under ice-covered lakes in the late winter. Numerical studies in this context tend to neglect the effects of nonuniform solar radiation on fluid motion in the lake interior. This research provides direct numerical simulations and the subsequent analysis of the resulting gravity-current-like flow, which propagates into an inversely stratified ambient with developing convection in the form of three-dimensional Rayleigh-Taylor instabilities. We find that with the chosen parameters, typical of an ice-covered lake, geometry plays a much larger role in its development and cessation.

[Phys. Rev. Fluids 9, 063501] Published Mon Jun 17, 2024

Author(s): Martin Smuda, Florian Kummer, Martin Oberlack, Dino Zrnić, and Günter Brenn

Liquid drops exhibit nonspherical surface shapes with strong deformations upon pinch-off from jets or sheets. The deformed state induces shape oscillations, which are analyzed both by the weakly nonlinear approach and high-order simulations using the extended Discontinuous Galerkin method as two alternative nonlinear theories to investigate the oscillations at moderate to large deformations. The coupling of oscillation modes is found to induce quasiperiodic motion, which is shown by Fourier power spectra of the frequencies. The interconversion of kinetic and surface energies during the oscillations at strong initial deformations is quantified by the numerical simulations.

[Phys. Rev. Fluids 9, 063601] Published Mon Jun 17, 2024

Author(s): P. V. Kashyap, Y. Duguet, and O. Dauchot

Linear stability analysis of the mean flow in turbulent plane channel flow in the large-scale pattern-forming range. Growth rate of the least stable mode as a function of streamwise and spanwise wavenumber α and β, respectively. Strict linear stability for all parameters is predicted for all parameters, suggesting that the mean flow stability does not explain pattern formation.

[Phys. Rev. Fluids 9, 063906] Published Mon Jun 17, 2024

Author(s): Bowen Ling, Runqing Shan, and Felipe P. J. de Barros

Multilayered porous media are prevalent in both natural and engineered systems, exerting significant influence on flow and transport processes. This study presents a hybrid analytical-numerical approach to compute and understand the dynamics between scalar properties and media characteristics in a coupled system with a two-dimensional free flow layer and a heterogeneous porous medium under laminar flow conditions. Our research underscores how variations in the permeability field within multilayered porous media profoundly influence and control scalar mixing behavior.

[Phys. Rev. Fluids 9, 064502] Published Mon Jun 17, 2024

Author(s): Joel Bracamontes-Ramirez and Bruce R. Sutherland

Vertically propagating internal wave packets incident upon a density staircase can resonantly excite natural modes of the staircase that then re-emit upward and downward propagating internal waves, changing the prediction for energy transmission of incident plane internal waves.

[Phys. Rev. Fluids 9, 064801] Published Mon Jun 17, 2024

Author(s): Chih-Tang Liao, Andrew Lemus, Ali Gürbüz, Alan C. H. Tsang, On Shun Pak, and Abdallah Daddi-Moussa-Ider

Microorganisms and synthetic microswimmers often encounter complex environments consisting of networks of obstacles embedded into viscous fluids. Such settings include biological media, such as mucus with filamentous networks, as well as environmental scenarios, including wet soil and aquifers. A fu…

[Phys. Rev. E 109, 065106] Published Thu Jun 13, 2024

Author(s): Tarcísio C. Déda, William R. Wolf, and Scott T. M. Dawson

In this work we propose a machine learning methodology for flow modeling and control design based on an iterative approach for training neural networks. We demonstrate that the methodology is able to achieve stabilization of complex nonlinear plants, such as an unstable confined flow past a cylinder. We also show that, through linearization of neural network models, we can use the methodology to conduct optimal sensor selection, as well as to perform unstable equilibrium estimation and stability analysis.

[Phys. Rev. Fluids 9, 063904] Published Wed Jun 12, 2024