Latest papers in fluid mechanics

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

Author(s): Mathieu Brasseur, Georges Jourdan, Christian Mariani, Diogo C. Barros, Marc Vandenboomgaerde, and Denis Souffland

An experimental investigation of the Richtmyer-Meshkov instability is conducted in spherical geometry where the displacement and the growth of the perturbations at the interface are given and compared to numerical simulations and new theoretical predictions. The results show that the instability amplitude initially grows, stabilizes, and then reduces before the arrival of the reflected shock wave. The theoretical model developed here agrees well with the experiments, although a time shift is observed in the stabilization regime. Furthermore, we show that convergent Rayleigh-Taylor effects are the main stabilizing mechanisms, and that compressibility has a negligible effect.

[Phys. Rev. Fluids 10, 014001] Published Mon Jan 06, 2025

Author(s): Andy Wu and Sanjiva K. Lele

Neural networks applied to turbulence modeling often do not learn locality or generalize to very high Reynolds number reasonably. Here, a two neural network architecture is introduced that learns the relevant neighborhood needed for sub-filter stress modeling through convolutions and the U-net architecture while generalizing reasonably to Reynolds numbers far larger than the training set on forced homogeneous isotropic turbulence and channel flow.

[Phys. Rev. Fluids 10, 014601] Published Mon Jan 06, 2025

Author(s): A. Leonid Heide and Maziar S. Hemati

This paper introduces an optimization framework for identifying sparse finite-amplitude perturbations that maximize transient growth in nonlinear systems. An iterative direct-adjoint looping algorithm is formulated based on the first-order necessary conditions for optimality. The method is applied to a reduced-order model of sinusoidal shear flow. Our results show that optimal sparse perturbations can achieve comparable energy amplification as the optimal non-sparse solution by triggering many of the same nonlinear modal interactions responsible for driving transient growth. We anticipate the approach will be a useful tool in future investigations into flow stability and control.

[Phys. Rev. Fluids 10, 014401] Published Thu Jan 02, 2025

Author(s): Miao Sun and Yanbo Xie

Previous work showed that a floating liquid bridge can be sustained under DC or high-frequency AC voltage, though the effects of frequency remain unclear. We investigated the stability of a micro-floating liquid bridge under periodic voltage pulses. The recorded current reveals the formation and breakup of the bridge as six distinct states of stability beyond high-speed imaging. Our results show that both pulse frequency and the electrocapillary number are crucial for liquid bridge stability. Considering the charging/discharging process of the system, we corrected the formation and breakup time, which well explained the observed delay in these processes.

[Phys. Rev. Fluids 9, 123701] Published Mon Dec 30, 2024

Author(s): Giulio Foggi Rota, Christian Amor, Soledad Le Clainche, and Marco Edoardo Rosti

Viscoelastic fluids like DNA solutions and polymer melts yield chaotic flows even with small inertial effects (quantified by the Reynolds number). Such turbulent motion is conventionally classified as elasto-inertial turbulence (EIT) or elastic turbulence (ET) when inertial effects are finite or vanishing. Our numerical study investigates the turbulent flow of viscoelastic fluids in planar channel flows over a wide range of Reynolds numbers. We discover that EIT and ET exhibit the same dynamical features and are thus the same. Our finding sheds light on low Reynolds number turbulence, with broader implications for materials science, industrial processes, and biology.

[Phys. Rev. Fluids 9, L122602] Published Mon Dec 30, 2024