Latest papers in fluid mechanics

Author(s): Shimin Zhang and Zhiliang Lin

Double-mode Faraday waves, excited near overlapping instability tongues, exhibit rich and interesting pattern-forming dynamics. This work experimentally studies the transitions from the five-fold mode to the eight-fold mode, governed by mode interactions and suppressions. With single-point and full spatial measurements, we quantify amplitude evolution and identify distinct supercritical (five-fold) and subcritical (eight-fold) excitations. The analysis reveals that incorporating fifth-order terms into the amplitude equations is essential for accurately capturing the observed transitional behaviors, thereby providing deeper insights into the multi-mode dynamics of Faraday wave systems.

[Phys. Rev. Fluids 10, 034003] Published Mon Mar 31, 2025

Author(s): Afroz F. Momin and Devang V. Khakhar

Hoppers are widely used in industrial granular processes. Discrete element simulations of the flow in an idealized wedge-shaped hopper, with frictionless walls and radial gravity, are compared to predictions of an exact theory by Savage, based on purely frictional rheology, and an extension of the theory based on a frictional-collisional rheology (μ-I). The agreement is excellent when the finite stress at the exit of the hopper is taken into account. The theory and simulations provide new physical insights into the converging flow, for varying flow rates, inter-particle friction, particle stiffness and particle diameter.

[Phys. Rev. Fluids 10, 034303] Published Mon Mar 31, 2025

Author(s): Qifu Wang, Jiaqi Zhang, David Bates, James J. Feng, Pengtao Yue, and Qianhong Wu

Rotation-induced traumatic brain injury is a serious health concern. We present a novel experimental and theoretical approach to studying fluid-structure interactions between soft matter and its liquid surroundings under rapid rotational impact. Our theoretical model, developed using the Arbitrary Lagrangian-Eulerian method, has been verified and validated against experimental data. This work establishes a strong foundation for future research into rotation-induced brain concussions, where the transient fluid-structure interaction between the cerebrospinal fluid and the soft brain matter plays a critical role in impact transmission and mitigation.

[Phys. Rev. Fluids 10, 030502] Published Fri Mar 28, 2025

Author(s): Herve Nganguia, Adedoyin Adegbuyi, Matthew Uffenheimer, and On Shun Pak

Encapsulating active particles within droplets to drive their motion presents exciting possibilities for biomedical applications, such as targeted drug delivery. In realistic biological and environmental settings, droplet interfaces often exhibit complex rheological behaviors that influence propulsion. This work investigates how surface shear and dilatational viscosities affect the motion of an active droplet, where a liquid droplet encloses an active particle modeled as a squirmer. The findings provide insights into the behavior of microswimmer-driven droplets in complex environments, paving the way for their potential biomedical and environmental applications.

[Phys. Rev. Fluids 10, 033104] Published Fri Mar 28, 2025

Author(s): Kai Wu, Long Chen, and Ming-Jiu Ni

Understanding the physics of wall mode in Rayleigh-Bénard convection under intense magnetic field is critical for heat transfer designs. This study reveals the flow and thermal behaviors of wall mode, uncovering how magnetic intensity, temperature difference, and aspect ratio affect fluid dynamics. The volume of wall modes plays an important role in heat transport, while the hot and cold wall surfaces with no-slip condition triggers reverse flows. These findings provide new insights into the heat transfer design of magnetohydrodynamics.

[Phys. Rev. Fluids 10, 033702] Published Fri Mar 28, 2025

Author(s): Jochem G. Meijer, Vincent Bertin, and Detlef Lohse

Tiny suspended particles are moved ahead of a freezing front, leaving behind pure ice. Yet, if particles are big or freezing occurs rapidly, they can get trapped in ice. Here, we investigate this phenomenon, focusing on the behavior of spherical objects, near the critical entrapment speed. Through experiments and theory we quantify how far particles travel before becoming entrapped. Moreover, we observe that two nearby particles either attract or repel during freezing, depending on their thermal conductivities. Our findings help to understand cluster formation during solidification, which we show to be analogous to clustering of particles at liquid interfaces, known as the Cheerios effect.

[Phys. Rev. Fluids 10, 034002] Published Fri Mar 28, 2025

Author(s): Running Hu, Zheng Yan, Runyuan Gan, Xinliang Li, and Changping Yu

In this paper, we investigate compressibility effects on helicity using structure functions and third-order relations. The helicity scaling law r2/3 holds in compressible turbulence, as helicity remains unaffected by compressive components. A new third-order relation introduces pressure and divergence terms, which are crucial in the dissipative range and drive inverse helicity cascades in the inertial range, respectively. Our findings clarify the role of compressibility in interscale helical dynamics, providing insights for its application in compressible turbulence and future theoretical advancements.

[Phys. Rev. Fluids 10, 034610] Published Fri Mar 28, 2025

Author(s): Saranraj Gururaj and Anirban Guha

In oceans, multiple inertia-gravity waves often coexist in a region. We study the stability of two coexisting plane inertia-gravity waves, with the same frequencies and wavevector norms. Specifically, we explore the decay of two primary waves through triadic resonant instabilities in cases where two primary waves have a common secondary wave, and this results in a 5-wave system composed of two different triads. We show that 5-wave systems are the dominant instabilities with higher growth rates than standard triads for latitudes greater than 9 degrees.

[Phys. Rev. Fluids 10, 034803] Published Fri Mar 28, 2025

Author(s): Donghun Kang and Seongkyu Lee

While the scattering of turbulent flows by an edge radiates sound waves into the far field, the roles of hydrodynamic and acoustic pressures remain unclear. This study examines these components to elucidate their roles and characteristics, focusing on trailing-edge noise through numerical and analytical approaches. Hydrodynamic pressure, characterized by streamwise turbulence, exhibits out-of-phase and incoherent behavior along the wall, forming pseudo-sound sources. In contrast, scattered acoustic pressure, governed by spanwise-coherent structures with weak energy and in-phase waves along the wall, is responsible for far-field sound radiation.

[Phys. Rev. Fluids 10, 034609] Published Thu Mar 27, 2025

Author(s): Siddhant Jain, Saini Jatin Rao, and Saptarshi Basu

Vortex rings (VRs) are intriguing fluidic structures capable of self-propulsion once created. We experimentally investigate the behavior of a VR as it interacts with perforated plates set at different angles. Remarkably, a single VR splits into two distinct VRs when the included angle (θ ≤ 120°) is small. Moreover, using n-faced perforated surfaces makes it possible to generate multiple VRs from a single vortex. On the other hand, this process can be suppressed by adjusting the θ values. The study explores key phenomena such as the growth of mushroom-shaped structures before interaction, the formation, and interaction of jets during the vortex impingement, and the subsequent reformation.

[Phys. Rev. Fluids 10, 034703] Published Thu Mar 27, 2025

Author(s): Rick D. M. Jansen, Ralf R. L. Reinartz, Haoyu Zhu, Rudie P. J. Kunnen, and Herman J. H. Clercx

Thermophoresis is a force exerted on particles in nonisothermal flows, acting opposite to the thermal gradient and potentially dominant in rarefied conditions. This force is not well understood in the transition regime, where the mean-free path of gas molecules, λ, is comparable to the particle radi…

[Phys. Rev. E 111, 035106] Published Tue Mar 25, 2025

Author(s): Hyuga Yasuda, Hiroaki Katsuragi, and Makoto Katsura

A simple one-dimensional power law model was proposed based on the assumption that the product of the water permeability and the pressure gradient is proportional to the cube of the water saturation. This model is semi-quantitatively consistent with the experimental results and suggests that the role of small gradients in water saturation in the wet region can not be ignored in determining the transition point from a constant rate period (CRP) to a falling rate period (FRP) in evaporation rates.

[Phys. Rev. Fluids 10, 034302] Published Mon Mar 24, 2025

Author(s): Andrey Pototsky, Aldo Figueroa, José Olvera-Orozco, Misael Álvarez-Jiménez, Sergio Cuevas, and Sergey A. Suslov

Electromagnetically driven large-scale vortices appear in horizontal electrically conducting soap films formed between two concentric cylindrical electrodes with the radii of several centimeters. In nonuniform magnetic fields formed by conventional permanent magnets, instability of the base flow develops if the applied DC voltage exceeds several volts. The number of vortices is controlled by the aspect ratio of the radii of the electrodes.

[Phys. Rev. Fluids 10, 034802] Published Mon Mar 24, 2025

Author(s): Fabian Karl Henn and Karen Alim

Inside the small intestine, the body absorbs most nutrients from chyme, a Non-Newtonian fluid formed by gastric disintegration of food. Despite its critical role in digestion, the impact of chyme’s rheology remains poorly understood. Using finite-element simulations, we reveal how viscosity governs nutrient uptake in intestinal contraction patterns. Our findings show that shear-thinning enhances absorption without compromising waste clearance, offering new insights into intestinal transport and disease prevention.

[Phys. Rev. Fluids 10, 033103] Published Fri Mar 21, 2025

Author(s): Zhuo Ma, Xiaofeng Guo, Laurent Royon, and Philippe Brunet

We study the streaming flow induced by periodic forcing on a fluid bounded in a millimeter-sized channel with a wedge obstacle on one of its walls. Using both experimental and numerical approaches across relevant parameter ranges, we observe different regimes of symmetric, transitional, and asymmetric flows for a large range of forcing amplitudes. We show regimes with an asymmetrical pair of streaming vortices under large vibration amplitudes at 280 Hz, and also evidence of slow-oscillations of symmetric vortices in a transitional mode. The radius of curvature of the wedge tip is found to be crucial for the existence range of these regimes.

[Phys. Rev. Fluids 10, 034102] Published Fri Mar 21, 2025

Author(s): Timothée Jamin, Michael Berhanu, and Eric Falcon

We experimentally study turbulence in water close to an air-water interface using an experimental setup based on the randomly actuated synthetic jet array forcing. We are able to tune the turbulence intensity by varying the flow of a unique pump, while each jet is controlled by a solenoid valve. Particle image velocimetry measurements are made to characterize the turbulent fluctuations becoming strongly anisotropic when approaching the free surface. The results are compared to the rapid distortion theory and stratified turbulence model.

[Phys. Rev. Fluids 10, 034608] Published Fri Mar 21, 2025

Author(s): Ilan M. L. Upfal, Yuanhang Zhu, Eric Handy-Cardenas, and Kenneth Breuer

Compliant membrane oscillating foil turbines (OFTs) can enhance power generation by stabilizing leading-edge vortices (LEVs), a key mechanism for lift. Through experiments in a water flume, we map the performance of compliant OFTs across a broad range of kinematics and isolate the roles of camber and extensibility in LEV stabilization. Membrane extensibility is shown to be critical for dynamic decambering at high angles of attack, delaying stall and improving lift and power, while camber alone suffices at low angles of attack. This study provides new insights into optimizing compliant OFTs for renewable energy applications.

[Phys. Rev. Fluids 10, 034702] Published Thu Mar 20, 2025