Latest papers in fluid mechanics

Author(s): Tristan Gilet and Loïc Tadrist

During heavy rainstorms, how can pathogenic spores at the surface of plant leaves travel upward and contaminate other leaves above? The spores are released in the sessile drops left on the leaves by previous raindrops. In this manuscript, we show that upon impact of a large raindrop, a leaf may strongly vibrate. The subsequent inertial forces may be sufficient to expel water from its surface. We describe this droplet ejection mechanism as a function of both leaf and raindrop properties. The droplets inherit from the leaf velocity, so some of them can be shot upward. This ejection mechanism likely induces a significant upward flux of biological material during rainstorms.

[Phys. Rev. Fluids 10, 053601] Published Fri May 02, 2025

Author(s): Prateek Gupta and Satish Kumar

Motivated by the need to improve fundamental understanding of multilayer coating on discrete objects, we consider a model problem involving the flow of bilayer thin liquid films on rotating cylinders. A parametric study reveals that the critical rotation rate required to cause motion of liquid lobes that form due to gravitational drainage is lowered for a more viscous and thicker inner film due to an increase in viscous forces. These properties of the inner layer also lead to a reduction in the amplitude of temporal oscillations in the film thickness. In addition to advancing fundamental understanding, we suggest strategies for improving the uniformity of coatings on discrete objects.

[Phys. Rev. Fluids 10, 054001] Published Fri May 02, 2025

Author(s): Shruti Pandey and V. Shankar

The recently discovered polymer diffusive instability (PDI) in rectilinear flows of an Oldroyd-B fluid has wavelengths of the order of the size of the polymer for realistic polymer diffusivities, raising a question on the applicability of continuum constitutive equations. We show, using the Giesekus model (augmented with stress diffusion), that the PDI is rapidly suppressed as the anisotropy parameter is increased, suggesting that anisotropic diffusion needs to be incorporated in order to obtain physically consistent results, either in stability calculations or in direct numerical simulations.

[Phys. Rev. Fluids 10, 053301] Published Thu May 01, 2025

Author(s): Qiang Zhu and Qing Xiao

Most existing propulsion systems rely on pressure for thrust generation, with shear stress being a major source of drag associated with skin friction. In this study, we propose a novel thrust-generation system using shear stress for thrust production. It features a barrel-shaped body whose outer membrane circulates in a tank-treading manner. Through numerical simulations, the feasibility of this design has been confirmed. The underlying physics and the potential performance have also been explored.

[Phys. Rev. Fluids 10, 054101] Published Thu May 01, 2025

Author(s): Yanxuan Shao, Jean-Regis Angilella, and Adilson E. Motter

Microfluidic systems have traditionally relied on external hardware or compliant structures to generate flow rate oscillations. Here, we demonstrate that persistent oscillations and even chaotic behavior can spontaneously emerge without external modulation, deformable structures, or fluid compressibility. Through a combination of numerical simulations and a reduced model, we uncover a mechanism governed by fluid inertia that drives this behavior at moderate Reynolds numbers. These findings expand the design space for on-chip flow control and reveal new opportunities for microfluidic timing, precision control, and chaos-based applications.

[Phys. Rev. Fluids 10, 054401] Published Thu May 01, 2025

Author(s): Wandrille Ruffenach, Lucas Fery, and Bérengère Dubrulle

This study presents a simplified model for shear flows developed to capture essential features of turbulence using a sparse representation based on intense structures called vortons. These dynamically regularized quasi-singularities interact with large-scale shear and give rise to two distinct flow regimes: a laminar regime governed by large-scale dissipation and a turbulent regime driven by vorton activity. Remarkably, the model reproduces power-law scaling behaviors consistent with classical turbulence, offering a compact yet insightful tool for investigating energy transfer and dissipation in complex flows.

[Phys. Rev. Fluids 10, 054601] Published Thu May 01, 2025

Author(s): N. S. Satpathi, G. S. G. Reddy, and A. K. Sen

Controlling the behavior of impacting droplets continues to remain a challenge. We demonstrate a simple method of inclining a plane superhydrophobic surface with a sudden wettability change in the form of a superhydrophilic spot to control the droplet impact dynamics. We find that, depending on the …

[Phys. Rev. E 111, 055101] Published Thu May 01, 2025

Author(s): Raffaello Foldes, Raffaele Marino, Silvio Sergio Cerri, and Enrico Camporeale

We studied the feedback of extreme vertical velocity drafts on the dynamics of stratified turbulent flows using a coarse-graining approach. This approach allowed for a local-in-scale analysis while preserving spatial detail, which is critical for assessing energy transfer and conversion in large-scale intermittent flows of geophysical interest. We found that vertical drafts may act as a local energy injection mechanism throughout the flow domain, affecting the exchange between kinetic and potential energy.

[Phys. Rev. Fluids 10, 043803] Published Wed Apr 30, 2025

Author(s): Hui Zhao, Xiangchun Xuan, and Ning Wu

Theory and simulation are used to demonstrate that the concentration polarization induced electro-osmotic (CPEO) flow is the origin of the experimentally observed nonlinear electrokinetic flow near a charged dielectric corner. The CPEO explains many experimentally observed electrokinetic phenomena that cannot be captured by existing electrokinetic theories. The CPEO can become a versatile technique in the microfluidic toolbox and open many new possibilities to use dielectric structures for fluidic flow control.

[Phys. Rev. Fluids 10, 044203] Published Wed Apr 30, 2025

Author(s): Scott K. Hansen and Daniel O'Malley

We consider conditions for minimum energy dissipation and advective travel time along path lines for potential flows in heterogeneous porous and fractured media. The work employs some concepts and techniques not often seen in the literature on Darcy (and cubic law) flows, including M. King Hubbert’s energy-based conception and variational methods. We explain a seemingly surprising result concerning how travel time through a series of fracture segments responds to small, local aperture perturbations.

[Phys. Rev. Fluids 10, 043802] Published Mon Apr 28, 2025

Author(s): Mahdi Saeedipour and Simon Schneiderbauer

This study investigates the systematic connection between the statistics of non-decaying homogeneous isotropic turbulence and droplet fragmentation outcomes, based on the concept of the enstrophy transport equation. Analysis of the interface-resolved direct numerical simulations (DNS) underlines the role of different vorticity generation mechanisms, such as vortex stretching and surface tension, in determining the size of the largest stable droplet during turbulent fragmentation known as the Kolmogorov-Hinze scale. The findings serve as the basis for future theory development under more complex turbulent fragmentation conditions.

[Phys. Rev. Fluids 10, 044301] Published Mon Apr 28, 2025

Author(s): M. Hausmann and B. van Wachem

Being able to accurately predict the flow near walls with preferably coarse resolutions is a key challenge in most practical flow applications. However, the wall-modeled large eddy simulations (WMLES) commonly applied typically rely on ad hoc interventions, such as assuming a mean velocity profile near the wall instead of the instantaneous filtered velocity profile. In the present paper, classical filtering is extended to domains confined by walls using volume-filtering. By rigorous application of volume-filtering, we derive a consistent wall-modeling framework that we refer to as volume-filtered WMLES.

[Phys. Rev. Fluids 10, 044604] Published Mon Apr 28, 2025

Author(s): Dhawal Buaria and Alain Pumir

Are extreme events in turbulence universal? While small-scale universality has long been accepted for some low-order statistics like the energy spectra, its validity for intense, intermittent fluctuations remains unclear. Using state-of-the-art direct numerical simulations and laboratory experiments, we analyze extreme velocity gradients across several different turbulent flows, and uncover striking universal behavior not only in scaling laws, but also in their detailed tensorial structure. Our findings support a deeper level of universality than previously thought, with profound implications for theory and modeling.

[Phys. Rev. Fluids 10, L042601] Published Mon Apr 28, 2025

Author(s): E. Jurčišinová, M. Jurčišin, and R. Remecký

The scaling inertial-range behavior of the single-time two-point correlation functions of the weak magnetic field, passively advected by the turbulent velocity field driven by the stochastic Navier-Stokes equation, is investigated in the framework of the field-theoretic renormalization group approac…

[Phys. Rev. E 111, 045108] Published Mon Apr 28, 2025

Author(s): Hannah-May D'Ambrosio, Stephen K. Wilson, Alexander W. Wray, and Brian R. Duffy

A comprehensive study of the effect of gravity-induced shape change on the diffusion-limited evaporation of thin sessile and pendant droplets on a horizontal substrate is performed. Specifically, theoretical predictions for the evolution, and hence the lifetime, of sessile and pendant droplets evapo…

[Phys. Rev. E 111, 045107] Published Fri Apr 25, 2025

Author(s): Alec Menzer, Yu Pan, George V. Lauder, and Haibo Dong

Fish schooling is believed to provide benefits by allowing individuals to leverage vortices generated by nearby fish, thereby improving their performance. While prior works have characterized horizontal planar formations of fish, our comprehensive analysis of the hydrodynamics in the vertical diamond formation reveals significant interactions among vertically arranged fish. In the densest vertical diamond formation, fin-fin, body-body, wake-body, and wake-fin interactions enhance force generation and propulsive efficiency for each individual in the school. The findings of this study could guide school configurations that enhance the performance of fish-inspired bio-robotic swarms.

[Phys. Rev. Fluids 10, 043104] Published Thu Apr 24, 2025

Author(s): Yan Xia, Zhaosheng Yu, Minkang Zhang, Zhaowu Lin, and Zhenyu Ouyang

In this work, we investigate the swimming dynamics of a spheroidal squirmer near a flat wall for various aspect ratios using the direct-forcing fictitious domain method. Our results show that the swimming mode of a strong pusher undergoes the transition from either oscillating or escaping to crawlin…

[Phys. Rev. E 111, 045106] Published Wed Apr 23, 2025

Author(s): Clément Caillaud, Guillaume Lehnasch, Eduardo Martini, and Peter Jordan

This numerical study delves into the complex dynamics of transitional hypersonic boundary layers, examining how streaks—elongated flow structures—affect linear instability mechanisms. By exploring the interplay between streak amplitude and boundary layer instabilities, the research uncovers intricate growth mechanisms of the first and second Mack modes, which differ significantly from idealized conditions without streaks. The study proposes a clear classification of growing instabilities and analyses modified growth trends. These insights provide valuable perspectives on potential pathways to turbulence in distorted boundary layers, contributing to advancements in transition prediction.

[Phys. Rev. Fluids 10, 043902] Published Tue Apr 22, 2025

Author(s): Judai Masugi, Takeshi Shoji, Yoshihiro Nakazumi, Ryota Fujii, Takuya Tomidokoro, Shigeru Tachibana, and Takeshi Yokomori

Lean premixed hydrogen combustion is a promising technology for reducing NOₓ and CO₂ emissions in gas turbines, but suffers from thermoacoustic instabilities. This study experimentally investigates the influence of the Lewis number on hydrogen and methane premixed flames under thermoacoustic instability in a low-swirl combustor. Simultaneous measurements of pressure fluctuations, OH* chemiluminescence, and PIV reveal that the pressure fluctuation in hydrogen flame is three times larger than that in methane flame, highlighting the significant role of the Lewis number in flame–flow interactions.

[Phys. Rev. Fluids 10, 043201] Published Mon Apr 21, 2025

Author(s): Peter S. B. Szabo and Christoph Egbers

This study examines the influence of an inhomogeneous external electric field on thermoelectrohydrodynamic (TEHD) convection and its impact on heat transfer enhancement in a dielectric fluid layer. TEHD convection arises when an external electric field interacts with a nonisothermal fluid, where ele…

[Phys. Rev. E 111, 045105] Published Mon Apr 21, 2025