Latest papers in fluid mechanics

Author(s): Christopher J. Camobreco, Alban Pothérat, and Gregory J. Sheard

This work investigates efficient routes to turbulence in quasi-two-dimensional (Q2D) shear flows. When the base flow is steady, transient growth is modest, as the initial perturbations are two-dimensional. With the addition of an oscillatory base flow component, the transient growth of even two-dimensional initial perturbations increases dramatically. However, as has been shown for three-dimensional flows, this transient growth proves to be almost entirely modal intracyclic growth, rather than non-normal growth, which delays sustained turbulence. Thus, in these Q2D flows, a non-oscillatory driving force sustains turbulence more efficiently than a pulsatile one.

[Phys. Rev. Fluids 10, 023905] Published Tue Feb 25, 2025

Author(s): Christopher J. Camobreco, Alban Pothérat, and Gregory J. Sheard

This work investigates efficient routes to turbulence in quasi-two-dimensional (Q2D) shear flows. When the base flow is steady, transient growth is modest, as the initial perturbations are two-dimensional. With the addition of an oscillatory base flow component, the transient growth of even two-dimensional initial perturbations increases dramatically. However, as has been shown for three-dimensional flows, this transient growth proves to be almost entirely modal intracyclic growth, rather than non-normal growth, which delays sustained turbulence. Thus, in these Q2D flows, a non-oscillatory driving force sustains turbulence more efficiently than a pulsatile one.

[Phys. Rev. Fluids 10, 023905] Published Tue Feb 25, 2025

Author(s): Toshiyuki Doi

A microscale lubrication flow of a gas between rotating eccentric circular cylinders is studied on the basis of kinetic theory. Two flows are compared: one in which only the inner cylinder rotates, and the other in which only the outer cylinder rotates at the same circumferential velocity. The difference in the lubrication performance between the two flows, which is small for a small Knudsen number, becomes evident as the Knudsen number increases. The physical mechanism is discussed using the lubrication equation derived from the Boltzmann equation.

[Phys. Rev. Fluids 10, 024201] Published Tue Feb 25, 2025

Author(s): Yuhan Li, Mingbo Li, Lu-wen Zhang, and Benlong Wang

Shock-induced cavitation in saline-rich seawater—where chloride, sodium, sulfate, and magnesium ions comprise over 90%—involves two key processes: bulk vapor nucleation and gas nanobubble expansion. This study employs all-atom molecular dynamics simulations to provide a nanoscopic perspective on cavitation inception under transient pressure fluctuations. It examines how ionic specificity and concentration affect these processes by discussing hydrogen bond density, interfacial molecular orientation, charge distribution, and surface tension. The findings demonstrate that ionic strength and radius govern water–water interactions, thereby influencing cavitation characteristics.

[Phys. Rev. Fluids 10, 024202] Published Tue Feb 25, 2025

Author(s): Shuting Peng, Fuzhen Chen, Hong Yan, and Fan Liu

We simulate the dynamics of tandem double droplets accelerated by uniform airflow. The deformation of the tandem droplets under different dimensionless parameters has been studied. The shape of the droplets is influenced by the vortex structure in the recirculation zone and the Rayleigh-Taylor instability (RTI). Decreasing the Reynolds number and the relative distance between droplets, as well as increasing the liquid/gas density ratio, increases the inhibitory effect of the leading droplet on the deformation of the trailing droplet. Finally, a predictive model was proposed to describe the temporal evolution of the radius of tandem droplets.

[Phys. Rev. Fluids 10, 024304] Published Tue Feb 25, 2025

Author(s): Han Huang, Shuaiqi Zhao, Rui Zhang, Binbin Pei, Kunpeng Zhao, and Bofeng Bai

We use a four-way coupled numerical approach to investigate dynamics of suspended cohesive particles in Rayleigh-Bénard turbulence. The Stokes drag, cohesive, and direct contact forces between primary particles are included, yielding the flocs’ aggregation, breakage, and deformation. We find that the initial increase of the average floc size is a transient flocculation phase, which is followed by an equilibrium phase with a stable average floc size, due to a balance of aggregation and breakage. In contrast to the traditional perspective, in which local particle accumulation is due to gravity, we find that suspended particles still tend to accumulate in the bottom hot boundary layer region.

[Phys. Rev. Fluids 10, 024305] Published Tue Feb 25, 2025

Author(s): Jason Stafford, Nwachukwu Uzo, Enrico Piccoli, Camille Petit, and Omar K. Matar

We examine large-amplitude wave formation on thin films flowing over a rapidly spinning disk with experiments and direct numerical simulations. Our results capture the transition from stationary two-dimensional spiral to fully three-dimensional waves.

[Phys. Rev. Fluids 10, 024805] Published Tue Feb 25, 2025

Author(s): Elias Huseby, Josephine Gissinger, Fabien Candelier, Nimish Pujara, Gautier Verhille, Bernhard Mehlig, and Greg Voth

We study the design of chiral particle shapes that couple translation to rotation in viscous fluid flow. Despite the importance of chiral design in many areas of science, there isn’t a known hierarchy of increasingly complex geometry with translation-rotation coupling ranging from simple to the general case. We identify helical ribbons as particles with strong translation-rotation coupling that can be tuned from simple axisymmetric behavior through general co-centered dynamics by changing length. During sedimentation, even these simple particles show quasiperiodic angular dynamics with complex spatial trajectories that can be unconfined for special initial orientations.

[Phys. Rev. Fluids 10, 024101] Published Mon Feb 24, 2025

Author(s): Elias Huseby, Josephine Gissinger, Fabien Candelier, Nimish Pujara, Gautier Verhille, Bernhard Mehlig, and Greg Voth

We study the design of chiral particle shapes that couple translation to rotation in viscous fluid flow. Despite the importance of chiral design in many areas of science, there isn’t a known hierarchy of increasingly complex geometry with translation-rotation coupling ranging from simple to the general case. We identify helical ribbons as particles with strong translation-rotation coupling that can be tuned from simple axisymmetric behavior through general co-centered dynamics by changing length. During sedimentation, even these simple particles show quasiperiodic angular dynamics with complex spatial trajectories that can be unconfined for special initial orientations.

[Phys. Rev. Fluids 10, 024101] Published Mon Feb 24, 2025

Author(s): Vaseem A. Shaik and Gwynn J. Elfring

We analyze the mixing induced by a model swimmer, the spherical squirmer, in density stratified fluids. Our findings indicate that the mixing by a squirmer is much larger than that caused by a point-sized swimmer (like force-dipole), although still small in weak stratification relevant to the ocean. Equivalent results are also obtained for a homogeneous dilute suspension of noninteracting squirmers.

[Phys. Rev. Fluids 10, 024102] Published Mon Feb 24, 2025

Author(s): Vaseem A. Shaik and Gwynn J. Elfring

We analyze the mixing induced by a model swimmer, the spherical squirmer, in density stratified fluids. Our findings indicate that the mixing by a squirmer is much larger than that caused by a point-sized swimmer (like force-dipole), although still small in weak stratification relevant to the ocean. Equivalent results are also obtained for a homogeneous dilute suspension of noninteracting squirmers.

[Phys. Rev. Fluids 10, 024102] Published Mon Feb 24, 2025

Author(s): Mingbao Zhang, Zhiguo Tian, Yunfan Huang, and Moran Wang

This study examines gas flow in porous media, finding four regimes: slip, Darcy, inertia, and turbulence. After scaling the Forchheimer equation, we introduce a dimensionless number, Rd, which provides a more physically grounded criterion for the transition to the inertia regime. Through experimental validations, the new mechanism also shows how gas slip effects influence flow at low permeability. These insights contribute to advancing both theoretical frameworks and experimental studies of gas flow in porous systems.

[Phys. Rev. Fluids 10, 024303] Published Mon Feb 24, 2025

Author(s): Alessia Ferraro, Gregory P. Chini, and T. M. Schneider

We derive a two-dimensional (2D) extension of a recently developed formalism for slow-fast quasilinear (QL) systems subject to fast instabilities. The emergent dynamics of these systems is characterized by a slow evolution of (suitably defined) mean fields coupled to marginally stable, fast fluctuat…

[Phys. Rev. E 111, 025105] Published Mon Feb 24, 2025

Author(s): G. Sanfins, F. Ramos, and D. Naiff

In this work, we introduce a neural network algorithm designed to automatically identify similarity relations from data. By uncovering these similarity relations, our network approximates the underlying physical laws that relate dimensionless quantities to their dimensionless variables and coefficie…

[Phys. Rev. E 111, 025106] Published Mon Feb 24, 2025

Author(s): Nicholas Pak, Elise Theriot, Denis Aslangil, Andrew Lawrie, and Arindam Banerjee

The dynamic properties of an interfacial flow between heavy and light incompressible fluids that are initially Rayleigh-Taylor unstable and are subjected to an external acceleration field oriented in opposition to the density gradient are studied. Rayleigh-Taylor instability occurs in nature with a …

[Phys. Rev. E 111, 025107] Published Mon Feb 24, 2025

Author(s): Xiaoqiang Sun, Hong Yan, and Fuzhen Chen

A series of turbulence-droplet interactions with realistic density ratios encountered in an aeroengine combustor are simulated and the effect of droplet size is investigated. It is shown that droplets present periphery shedding at the initial stage of breakup and are stretched into a disk-like shape before final breakup. The vortical turbulence helps to deform and break up the interface. The general turbulent characteristics are similar to single-phase flow and more perturbations are introduced by the gas-liquid interactions.

[Phys. Rev. Fluids 10, 024004] Published Fri Feb 21, 2025

Author(s): Xiaoqiang Sun, Hong Yan, and Fuzhen Chen

A series of turbulence-droplet interactions with realistic density ratios encountered in an aeroengine combustor are simulated and the effect of droplet size is investigated. It is shown that droplets present periphery shedding at the initial stage of breakup and are stretched into a disk-like shape before final breakup. The vortical turbulence helps to deform and break up the interface. The general turbulent characteristics are similar to single-phase flow and more perturbations are introduced by the gas-liquid interactions.

[Phys. Rev. Fluids 10, 024004] Published Fri Feb 21, 2025

Author(s): Mattias Brynjell-Rahkola, Yohann Duguet, and Thomas Boeck

The transition route from laminar to turbulent flow in a magnetohydrodynamic duct with a square cross-section is investigated in the limit of low magnetic Reynolds number. In the presence of a transverse magnetic field, Hartmann and Shercliff layers are present on the walls orthogonal and parallel to the field direction, respectively. Independently of the initial location of a finite perturbation in either Shercliff or Hartmann layers, transition relies on a tripping of the Shercliff layer by perturbations, while the Hartmann layer plays a passive role. This is explained, using a dynamical systems interpretation, by the spatial localization of the edge states in the Shercliff layer.

[Phys. Rev. Fluids 10, 023903] Published Thu Feb 20, 2025

Author(s): Mattias Brynjell-Rahkola, Yohann Duguet, and Thomas Boeck

The transition route from laminar to turbulent flow in a magnetohydrodynamic duct with a square cross-section is investigated in the limit of low magnetic Reynolds number. In the presence of a transverse magnetic field, Hartmann and Shercliff layers are present on the walls orthogonal and parallel to the field direction, respectively. Independently of the initial location of a finite perturbation in either Shercliff or Hartmann layers, transition relies on a tripping of the Shercliff layer by perturbations, while the Hartmann layer plays a passive role. This is explained, using a dynamical systems interpretation, by the spatial localization of the edge states in the Shercliff layer.

[Phys. Rev. Fluids 10, 023903] Published Thu Feb 20, 2025

Author(s): Ning Zhou, Zhigang Zhai, and Xisheng Luo

The growth of a shock-induced heavy fluid layer with dual-mode perturbations is investigated. Processes of the disturbed reverberating waves interacting with the layer are modeled theoretically. By considering the reverberating waves, growth of the heavy fluid layer can be well manipulated.

[Phys. Rev. Fluids 10, 023904] Published Thu Feb 20, 2025