Latest papers in fluid mechanics

Colloidal diffusiophoresis in crossed electrolyte gradients: Experimental demonstration of an “action-at-a-distance” effect predicted by the Nernst-Planck equations

Physical Review Fluids - Thu, 01/04/2024 - 10:00

Author(s): Ian Williams, Patrick B. Warren, Richard P. Sear, and Joseph L. Keddie

In an externally imposed electrolyte (salt) concentration gradient, charged colloids drift at speeds of order one micrometre per second. This phenomenon is known as diffusiophoresis. In systems with multiple salts and “crossed” salt gradients, a nonlocal component of the electric field associated wi…


[Phys. Rev. Fluids 9, 014201] Published Thu Jan 04, 2024

Attraction of neutrally buoyant deformable particles towards a vortex

Physical Review Fluids - Thu, 01/04/2024 - 10:00

Author(s): Yutaro Fujiki, Hideto Awai, Yutaro Motoori, and Susumu Goto

Deformable elastic particles can accumulate around a vortex center even if the particle is neutrally buoyant. The angle between the deformed particle and the pathline plays important roles in this accumulation process. In this paper, we propose a simple model to explain this interesting accumulation phenomenon.


[Phys. Rev. Fluids 9, 014301] Published Thu Jan 04, 2024

Off-lattice Boltzmann simulation of conjugate heat transfer for natural convection in two-dimensional cavities

Physical Review E - Wed, 01/03/2024 - 10:00

Author(s): Kuldeep Tolia, Sai Ravi Gupta Polasanapalli, and Kameswararao Anupindi

This study addresses the inadequacy of isothermal wall conditions in predicting accurate flow features and thermal effects in multicomponent systems. A finite-difference characteristic-based off-lattice Boltzmann method (OLBM) with a source term-based conjugate heat transfer (CHT) model is utilized …


[Phys. Rev. E 109, 015101] Published Wed Jan 03, 2024

Self-diffusiophoresis with bulk reaction

Physical Review Fluids - Wed, 01/03/2024 - 10:00

Author(s): Rodolfo Brandão, Gunnar G. Peng, David Saintillan, and Ehud Yariv

Catalytic motors, which self-propel in a liquid due to an inhomogeneous surface reaction, constitute an important illustration of active matter in a non-biological context. Prevailing models of the associated self-diffusiophoretic transport assume a chemical reaction at the boundary of the swimmer. We here address the more realistic scenario where that reaction is balanced by a homogeneous reaction in the bulk. The associated diffusive transport of solute, described by two Damköhler numbers, exhibits a boundary-layer topology which is not encountered in the prevailing models.


[Phys. Rev. Fluids 9, 014001] Published Wed Jan 03, 2024

Asymmetric Kelvin-Helmholtz instabilities in stratified shear flows

Physical Review Fluids - Tue, 01/02/2024 - 10:00

Author(s): Adam J. K. Yang, Mary-Louise Timmermans, and Gregory A. Lawrence

This study elucidates the regime of fluid instabilities that can arise in a stratified shear flow when density and velocity interfaces are not aligned - a common occurrence in various geophysical flows. Through a combination of linear stability analysis and direct numerical simulations, we unveil a hybrid mode characterized by features of both Kelvin-Helmholtz and Holmboe instabilities. By quantifying the crucial role of asymmetry, our findings contribute to a refined understanding of the dynamics and mixing in these stratified shear flows.


[Phys. Rev. Fluids 9, 014501] Published Tue Jan 02, 2024

Effect of layer thickness for the bounce of a particle settling through a density transition layer

Physical Review E - Thu, 12/28/2023 - 10:00

Author(s): Shuhong Wang, Jiadong Wang, and Jian Deng

We study numerically a spherical particle settling through a density transition layer at moderate Reynolds numbers Reu=69∼259 for the upper fluid. We investigate how the transition layer thickness affects the particle's bouncing behavior as it crosses the interface. The previous intuitive understand…


[Phys. Rev. E 108, 065108] Published Thu Dec 28, 2023

Vorticity wave interaction, Krein collision, and exceptional points in shear flow instabilities

Physical Review E - Thu, 12/28/2023 - 10:00

Author(s): Cong Meng and Zhibin Guo

We relate the model of vorticity wave interaction to Krein collision, PT-symmetry breaking, and the formation of exceptional points in shear flow instabilities. We show that the dynamical system of coupled vorticity waves is a pseudo-Hermitian system with nonreciprocal coupling terms. Krein signatur…


[Phys. Rev. E 108, 065109] Published Thu Dec 28, 2023

Dynamic wetting experiments with nitrogen in a quasi-capillary tube

Physical Review Fluids - Thu, 12/28/2023 - 10:00

Author(s): Domenico Fiorini, Alessia Simonini, Johan Steelant, David Seveno, and Miguel Alfonso Mendez

We perform experiments with liquid nitrogen’s gas-liquid interface oscillations in a U-shaped quartz tube and investigate the wetting dynamics in inertia-dominated conditions. The experiments reveal a linear relationship between dynamic contact angle evolution and Capillary number in advancing conditions while the contact angle remains near equilibrium in receding conditions. An equivalent contact angle, derived from a model, shows the overall independence of the capillary pressure from the actual contact angle evolution. Theoretical analysis indicates viscous forces dominate in small tubes, while gravity and inertial forces govern larger tube oscillations.


[Phys. Rev. Fluids 8, 124004] Published Thu Dec 28, 2023

Unified description over time of heterogeneous condensation with quenched disorder

Physical Review E - Wed, 12/27/2023 - 10:00

Author(s): Ruddy Urbina and Wenceslao González-Viñas

We report experimental results on breath figures (BFs) observed on substrates with quenched disorder. The evolution of BFs is found to be primarily influenced by global parameters associated with boundary conditions. We investigate classical statistical measures and explore topological properties us…


[Phys. Rev. E 108, 065107] Published Wed Dec 27, 2023

Unsteady granular chute flows at high inertial numbers

Physical Review Fluids - Tue, 12/26/2023 - 10:00

Author(s): Satyabrata Patro, Anurag Tripathi, Sumit Kumar, and Anubhav Majumdar

High speed granular flows flowing over inclined surfaces are studied using discrete element method and continuum simulations. Significant slip velocity at the base and strong oscillations in the layer height are observed. The popular inertial-number-based JFP rheological model fails to capture the transient flow dynamics at high inertial numbers. Accounting for the layer dilatancy effect and the presence of normal stress difference is essential to accurately predict the average flow behavior. A modified rheological model recently proposed by the authors, accounting for all these effects describes the evolution of the high-speed granular flow very well for both low as well as high inertial numbers.


[Phys. Rev. Fluids 8, 124303] Published Tue Dec 26, 2023

Freezing of sessile droplet and frost halo formation

Physical Review Fluids - Fri, 12/22/2023 - 10:00

Author(s): Sivanandan Kavuri, George Karapetsas, Chander Shekhar Sharma, and Kirti Chandra Sahu

Freezing droplets are ubiquitous in many practical applications, like in aircraft and wind turbine icing, spray technologies, food and pharmaceutical engineering, and natural phenomena such as raindrop formation. In the context of sessile droplets, the freezing process unveils fascinating physics, featuring a frost halo on the substrate, the evolution of the liquid-ice interface, and the formation of a cusp-like morphology at the tip of the droplet. Our study explores the novel theoretical aspects of frost halo formation, revealing its intricate link to the inherent evaporation process during the initial freezing phases.


[Phys. Rev. Fluids 8, 124003] Published Fri Dec 22, 2023

Hydrodynamic interactions change the buckling threshold of parallel flexible sheets in shear flow

Physical Review Fluids - Fri, 12/22/2023 - 10:00

Author(s): Hugo Perrin, Heng Li, and Lorenzo Botto

Viscous-flow induced buckling modifies the morphology of sheet-like particles suspended in liquids. Experiments reveal that a pair of sheets can bend at a shear rate ten times lower than the buckling threshold defined for a single sheet. Using simulations and modeling, we demonstrate that this softening is due to hydrodynamic interactions. Our study suggests that the morphology of sheet-like particles in suspensions and the resulting rheology is not a purely material property, but also depends on particle concentration and microstructure.


[Phys. Rev. Fluids 8, 124103] Published Fri Dec 22, 2023

Numerical comparison of two-dimensional Navier-Stokes flows on the whole plane and the periodic domain

Physical Review Fluids - Fri, 12/22/2023 - 10:00

Author(s): Koji Ohkitani

A direct numerical comparison is made of two-dimensional Navier-Stokes flows between two different boundary conditions, namely the whole plane and a periodic domain. We study their differences after adjusting the Reynolds number. The norms generally decay faster on the periodic domain than on the whole space. In the case of a simple vortex merger the difference is appreciable, whereas the difference is small in the case of turbulence. This gives support to studying finite-energy turbulence under periodic boundary conditions.


[Phys. Rev. Fluids 8, 124607] Published Fri Dec 22, 2023

<i>A priori</i> screening of data-enabled turbulence models

Physical Review Fluids - Thu, 12/21/2023 - 10:00

Author(s): Peng E. S. Chen, Yuanwei Bin, Xiang I. A. Yang, Yipeng Shi, Mahdi Abkar, and George I. Park

A posteriori validation and verification of black box machine learned turbulence models is time consuming and is not always fruitful. We discuss a theoretical framework that allows a priori screening of machine-learned models that are based on feed-forward neural networks. It requires no knowledge of the weights and bias and only knowledge of the activation function. The method tells one whether a machine learned model preserves basic calibrations like the law of the wall.


[Phys. Rev. Fluids 8, 124606] Published Thu Dec 21, 2023

Amplitude of water pouring sound

Physical Review Fluids - Thu, 12/21/2023 - 10:00

Author(s): Mouad Boudina, Joonoh Kim, and Ho-Young Kim

The familiar pouring sound we all hear when preparing tea or coffee has been a rare topic of study so far, despite its importance in several applications. We experimentally find that the sound amplitude increases with the jet corrugation, indicating that thin jets are louder than thick ones for the same given height. When pouring from a high distance, the jet breaks up into impacting drops, and the amplitude increases with the jet length and diameter. Results show that the jet corrugation relates to the volume of entrained air, hence the pouring sound can enter as a practical method to measure water aeration rates.


[Phys. Rev. Fluids 8, L122002] Published Thu Dec 21, 2023

Prebifurcation enhancement of imbibition-drainage hysteresis cycles

Physical Review Fluids - Wed, 12/20/2023 - 10:00

Author(s): Ido Lavi, Lauren Rose, Ramon Planet, Jaume Casademunt, Stéphane Santucci, and Jordi Ortín

When flowing through disordered media, fluid-fluid interfaces are subjected to sharp capillary jumps that shape displacements at large scales. The intricacies of this phenomenon are hard to decipher due to the inherent stiffness and non-locality of the problem. Here we use an “imperfect” Hele-Shaw cell to elucidate the response to a single topographical defect as a function of the imposed flow rate, keeping to stable Saffman-Taylor conditions. Through imbibition-drainage experiments and numerical integration of a robust two-dimensional model we showcase the profound impact of the proximity to the fingering instability.


[Phys. Rev. Fluids 8, 124002] Published Wed Dec 20, 2023

Oscillatory flows in compliant conduits at arbitrary Womersley number

Physical Review Fluids - Wed, 12/20/2023 - 10:00

Author(s): Shrihari D. Pande, Xiaojia Wang, and Ivan C. Christov

Oscillatory flows in deformable tubes have been of intense interest since Womersley’s work in the 1950s. The solutions for the pressure, flow rate, and wave propagation along the tube are a cornerstone of biofluid mechanics. However, it is assumed that the hydrodynamic pressure can only cause infinitesimal wall deformations; the cross-sectional area cannot change. Yet, oscillatory flows do deform conduits to such an extent that a nonlinear pressure gradient develops. We derive and benchmark a reduced-order model (a single, complex-valued partial differential equation for the pressure) that captures two-way coupling between flow and deformation, without restrictions on the oscillation frequency.


[Phys. Rev. Fluids 8, 124102] Published Wed Dec 20, 2023

Dependence of scalar mixing on initial conditions in turbulent channel flow

Physical Review Fluids - Tue, 12/19/2023 - 10:00

Author(s): Milind Singh, Emmanuel Germaine, Laurent Mydlarski, and Luca Cortelezzi

Scalar-field initial conditions can have a strong effect on the evolution(s) of scalar fields and the rate at which mixing occurs. The effects of the scalar field initial conditions are studied by analyzing the evolution of three scalar fields with interfaces oriented normal to the streamwise, wall-normal, and transverse directions. When the interface is aligned normal to the mean velocity vector, higher rates of production and destruction of the scalar dissipation, as well as strong advection and stretching of the interface by the mean flow are observed. It is therefore recommended that scalar interfaces be aligned normal to the mean velocity vector to promote mixing within internal flows.


[Phys. Rev. Fluids 8, 124605] Published Tue Dec 19, 2023

Controlling the dewetting morphologies of thin liquid films by switchable substrates

Physical Review Fluids - Tue, 12/19/2023 - 10:00

Author(s): S. Zitz, A. Scagliarini, and J. Harting

Wetting of surfaces holds a crucial interest for diverse technological and societal areas, from nanotechnology to contagion dynamics. We propose the usage of substrates with time-varying wettability as a novel tool to solve a critical problem, namely the control of dewetting morphologies. A new numerical method, able to handle unprecedented system sizes in this context, is employed. We unveil the existence of a droplet-to-rivulet transition determined by the substrate adaptation rate. Our work paves an avenue for the application of simulations to study the complex dynamics of thin liquid films over switchable and adaptive substrates.


[Phys. Rev. Fluids 8, L122001] Published Tue Dec 19, 2023

Negatively buoyant vortices in the Boussinesq-Euler equations

Physical Review Fluids - Fri, 12/15/2023 - 10:00

Author(s): G. G. Rooney

This work investigates an idealized model of a finite-volume, cylindrical gravity current, placing it in a context with non-buoyant dipoles and atmospheric ‘modons’. In cross-section, the current presents as a semicircular vortex of dense fluid in an unstratified background. In the frame traveling with the current, the flow is in a steady-state, achieved by a balanced generation of baroclinic vorticity. Numerical experiments demonstrate how the steadiness of a single vortex depends upon this balance, and show that vortex interactions have similarities to those of solitary waves.


[Phys. Rev. Fluids 8, 123802] Published Fri Dec 15, 2023

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