Latest papers in fluid mechanics

Author(s): Yahua Liu, Seyed Ali Hosseini, Cong Liu, Milo Feinberg, Benedikt Dorschner, Zuankai Wang, and Ilya Karlin

Drops impacting superhydrophobic surfaces have a rim-lamella structure at maximum spreading. The volume ratio of these two components is shown to be Weber-independent and related to a new Weber-independent characteristic time, the transition time. Volume ratios from experiments and simulations at different Ohnesorge numbers are shown.

[Phys. Rev. Fluids 10, 013602] Published Thu Jan 16, 2025

Author(s): Hongyue Chen, Xianyu Nong, Bokun Zhao, Wenxuan Zhong, Kangqi Liu, Zhen Chen, and Duyang Zang

Coalescence of droplets is connected to fascinating interfacial fluid dynamics that is of great importance in a variety of natural and engineering systems. We here explore the growth dynamics of liquid bridges during droplet coalescence under acoustic levitation. We show that the early-time evolution of the liquid bridge follows a scaling law d∼t5 in the inertial regime, with different prefactors for horizontal and vertical growth. We also highlight the interplay between acoustic radiation pressure and Laplace pressures. A new dimensionless parameter, the Acoustic-Capillary Dynamics Number, is introduced to enhance our understanding of liquid bridge dynamics in acoustic fields.

[Phys. Rev. Fluids 10, 013603] Published Thu Jan 16, 2025

Author(s): Sagy R. Ephrati, Arnout Franken, Erwin Luesink, Paolo Cifani, and Bernard J. Geurts

We use a continuous data assimilation approach to obtain low-cost stand-alone computational models for fluid flows. A nudging method is used to enforce global flow statistics, yielding a data-driven stochastic model that obtains accurate flow representations at coarse grids at severely reduced computational costs. This is demonstrated for the two-dimensional Navier-Stokes equations and the quasi-geostrophic equations.

[Phys. Rev. Fluids 10, 013801] Published Thu Jan 16, 2025

Author(s): Haocheng Wu, Yang Xiang, Gaohua Li, and Zifei Yin

This study explores how distributed surface roughness influences separation-induced transition on a flat plate, under the influence of freestream turbulence and adverse pressure gradients. Using direct numerical simulations, the interactions between freestream perturbations and vortices generated by roughness elements are investigated. Results reveal that low roughness accelerates instability development without dominating the transition process, while higher roughness causes a more intensified vortex mixing process and directly results in transition to turbulence.

[Phys. Rev. Fluids 10, 013903] Published Thu Jan 16, 2025

Author(s): Aarshana R. Parekh and Rajeev K. Jaiman

This study examines how the unsteady wake from an upstream stationary cylinder impacts the flapping response of an elastic inverted foil. Through high-fidelity simulations, we identify a critical nondimensional bending rigidity above which wake interference effects result in distinct flapping dynamics governed by stiffness and mass ratio. Additionally, we propose a nondimensional parameter that captures the interplay between inertia and elasticity, offering insights into fluid-structure interactions with implications for renewable energy harvesting systems.

[Phys. Rev. Fluids 10, 014702] Published Thu Jan 16, 2025

Author(s): Nicolás P. Müller and Giorgio Krstulovic

This numerical study on two-dimensional (2D) turbulence reveals that transverse structure functions in the inverse energy cascade display anomalous scaling properties, differing from the self-similar behavior of longitudinal ones. Using direct numerical simulations of incompressible Navier-Stokes equations, this study shows a link between the scaling exponents of transverse structure functions and velocity circulation moments. These findings provide new insights into the dynamics of 2D turbulence, with implications for understanding geophysical flows.

[Phys. Rev. Fluids 10, L012601] Published Thu Jan 16, 2025

Author(s): Patrick J. Stofanak, Cheng-Nian Xiao, and Inanc Senocak

Heating a stratified fluid in a valley-shaped container triggers a self-organizing flow. Starting from a quiescent state, any infinitesimal disturbance leads the flow through a transient three-dimensional phase before settling into a two-dimensional steady state. This complex pathway arises from the dominance of viscous dissipation over buoyant production. The orderly transition between 3D and 2D, supported by linear theory, sets our findings apart from transient chaos. While the final pattern is not predicted by linear theory, several stages align well with it. Our example offers new insights into self-organization in fluid systems with geophysical and astrophysical implications.

[Phys. Rev. Fluids 10, 014402] Published Mon Jan 13, 2025

Author(s): Feihu Ke, Chung-Yee Kwok, and Kang Duan

We conduct experimental and theoretical investigations into the previously unexplored effects of intergranular bonds within cohesive granular skeletons on multiphase flow dynamics. We illuminate that fluid forces can become large enough to surpass bond strength, leading to bond breakage and fracture initiation as capillary numbers increase. A first-ever phase diagram of five distinct fluid-fluid-grain displacement morphologies is established under varying flow and cohesion conditions. Through dimensional analysis, we propose a fracturing number Nf* = 1 as a theoretical threshold to characterize the onset of fluid-induced fracturing in cohesive media.

[Phys. Rev. Fluids 10, 013902] Published Fri Jan 10, 2025

Author(s): Adam J. K. Yang, Mary-Louise Timmermans, Jason Olsthoorn, and Alexis K. Kaminski

Stratified flow instabilities play a critical role in particle sedimentation in marine environments, influencing the efficacy of marine carbon dioxide removal strategies. Using direct numerical simulations, we reveal how these instabilities enhance or inhibit settling across flow regimes. Our findings highlight the dynamic interplay between turbulence, stratification, and particle dynamics, providing new insights into optimizing carbon removal techniques.

[Phys. Rev. Fluids 10, 014501] Published Fri Jan 10, 2025

Author(s): Xingsi Ren, Dehao Xu, Jianchun Wang, and Shiyi Chen

Artificial-neural-network-based (ANN-based) subgrid-scale (SGS) models for turbulent channel flow often suffer from instability and poor generalization. Here, we propose an ANN-SGS model based on the strain-rate eigenframe and apply it to large eddy simulations of compressible turbulent channel flow. Our results indicate that the newly proposed model can predict flow statistics more accurately than traditional SGS models, and it also exhibits generalization capability for both Reynolds and Mach numbers.

[Phys. Rev. Fluids 10, 014603] Published Fri Jan 10, 2025

Author(s): Motonori Nakamura and Fujihiro Hamba

Motivated by countergradient diffusion phenomenon in the turbulent premixed flame, we discuss the effects of heat release on turbulence. We devised and implemented a direct numerical simulation of the turbulent Rayleigh flow generated by isotropic turbulence flowing into the Rayleigh flow. We show that countergradient diffusion of the turbulent heat flux occurs in the turbulent Rayleigh flow, and we discuss its mechanism based on the transport equations of the turbulent statistical quantities. It is shown that the released heat amplifies the density-internal energy correlation and contributes countergradient diffusion through the pressure gradient effect.

[Phys. Rev. Fluids 10, 014604] Published Fri Jan 10, 2025

Author(s): Alexis Commereuc, Emmanuelle Rio, and François Boulogne

Mitigating energy consumption in fluid transportation is crucial for industrial processes. Our research addresses this by investigating the reduction of friction in liquid foams on Slippery Liquid-Infused Porous Surfaces (SLIPS). These surfaces have asperities filled with oil, significantly reducing friction compared to smooth surfaces. While oil is unsuitable due to its anti-foaming properties, we propose a unique approach using self-SLIPS, introducing the idea that the foam liquid can serve as a lubricant. Our findings demonstrate that these passive surfaces can achieve a 25% reduction in foam friction, promising significant advancements in energy-efficient fluid transport.

[Phys. Rev. Fluids 10, L011601] Published Fri Jan 10, 2025

Author(s): S. A. Piriz, A. R. Piriz, and N. A. Tahir

A quasi-irrotational approximation for the linear Rayleigh-Taylor instability in elastic solids with finite thickness has been developed for the case in which the slab is in contact with a rigid wall. The approximation yields simple but still reasonably accurate expressions for the instability growt…

[Phys. Rev. E 111, 015102] Published Fri Jan 10, 2025

Author(s): Joel Daou and Prabakaran Rajamanickam

The hydrodynamic instabilities of propagating interfaces in Hele-Shaw channels or porous media under the influence of an imposed flow and gravity are investigated within the framework of Darcy’s law. The stability analysis pertains to an interface between two fluids with different densities, viscosities, and permeabilities, which can be susceptible to Darrieus-Landau, Saffman-Taylor, and Rayleigh-Taylor instabilities. An explicit dispersion relation is derived.

[Phys. Rev. Fluids 10, 013201] Published Thu Jan 09, 2025

Author(s): Djihane Benzeggouta, Benjamin Favier, and Michael Le Bars

Inspired by recent observations of stable cyclone patterns on the North and the South poles of Jupiter, we present observations of monopolar barotropic cyclones in a model experiment for atmospheric polar flows. We show, both experimentally and with idealized quasi-geostrophic simulations, that starting from an initial vortex, there are two evolution regimes depending on vortex strength relative to the local beta-effect across its surface: a Rossby wave emission dominated regime and a strong vortex regime. In the latter regime, the generated cyclone drifts in a northwest direction. We show that the “beta gyre” induced “beta drift” mechanism locally applies in our experimental polar plane.

[Phys. Rev. Fluids 10, 014701] Published Thu Jan 09, 2025

Author(s): Qiang Du, Yaguang Xie, Lei Xie, Ruonan Wang, Qingzong Xu, and Junqiang Zhu

Due to the inviscid cross-flow instability caused by the inflection point in radial velocity, both convective and absolute instabilities coexist in the rotating-disk boundary layer within rotor-stator cavities. To investigate the laminar-turbulent transition process through convective instability under specific roughness element excitation, this study employs numerical simulation with body force to simulate roughness elements. The findings reveal that under convective instability, the rotating-disk boundary layer initially exhibits stationary spiral waves mode, followed by the development of traveling spiral waves mode in the radial direction, ultimately transitioning to turbulence.

[Phys. Rev. Fluids 10, 013901] Published Wed Jan 08, 2025

Author(s): Shreyank Goel, Rakshith Gowda BT, and Dipin S. Pillai

Droplet dynamics in (di)electrowetting and dewetting on dielectric configuration is elucidated using a lubrication model. Electric field-modified Frumkin-Derjaguin theory through Lippmann’s principle of electrocapillarity is employed. The research uncovers a field strength dependent power-law relationship for the contact line motion that conforms to Tanner’s law for the case of critical field leading to complete wetting. Electrodewetting shows a faster retraction compared to wetting due to reduced viscous dissipation. These findings provide a new theoretical framework for electric field-driven wetting and dewetting, enabling advancements in digital microfluidics.

[Phys. Rev. Fluids 10, 014201] Published Wed Jan 08, 2025

Author(s): Xinyi Huang and Jiaqi J. L. Li

This work focuses on the impact of meandering on wake statistics in the stratified environment. The range of wake meandering increases in the vertical direction while wake height does not. Meandering does not directly change the velocity scaling, or the wake width and height, but it leads to deviation of the velocity profile from self-similarity, and the development of layered flow structures. We can accurately measure how meandering distorts the self-similar velocity profile and impacts scaling of the width and height, and thus how meandering changes the scaling of the velocity deficit.

[Phys. Rev. Fluids 10, 014602] Published Wed Jan 08, 2025

Author(s): Himanshi, Anirudh Singh Rana, and Vinay Kumar Gupta

The well-known Navier-Stokes-Fourier equations of fluid dynamics are, in general, not adequate for describing rarefied gas flows. Moreover, while the Stokes equations—a simplified version of the Navier-Stokes-Fourier equations—are effective in modeling slow and steady liquid flow past a sphere, they…

[Phys. Rev. E 111, 015101] Published Tue Jan 07, 2025

Author(s): Bauyrzhan K. Primkulov, Davis J. Evans, Joel B. Been, and John W. M. Bush

Pilot-wave hydrodynamics concerns the dynamics of droplets walking on a vibrating liquid bath, and forms the basis for the field of hydrodynamic quantum analogs. We here investigate a theoretical model that captures both vertical and horizontal drop dynamics. The model provides new rationale for a number of phenomena, including colinear swaying, intermittent walking, and chaotic speed oscillations, all of which are linked to variability in the droplet’s impact phase. Our study also highlights the degeneracy in the droplet’s vertical dynamics, consideration of which is essential for understanding the dynamics of droplets in confined geometries and interacting with standing Faraday waves.

[Phys. Rev. Fluids 10, 013601] Published Mon Jan 06, 2025