Latest papers in fluid mechanics

Author(s): Pengyu Shi

Bubbles rising near a vertical wall are known to bounce repeatedly when the Reynolds number (Re) exceeds about 65. This behavior contradicts potential flow theory, which suggests a consistently attractive transverse force. In this study, we demonstrate through numerical simulations that below a critical Re-dependent separation, the transverse force decreases with decreasing separation, potentially reversing from attractive to repulsive. We believe this reversal is responsible for the bouncing motion observed in freely near-wall rising bubbles.

[Phys. Rev. Fluids 9, 023601] Published Tue Feb 06, 2024

Author(s): J. H. Lowenstein

The Zhong-Zhang (ZZ) model is a one-degree-of-freedom dynamical system describing the motion of an insulating plate of length d floating on the upper surface of a convecting fluid, with locking at the boundaries. In the absence of noise, the system away from the boundaries is described by linear dif…

[Phys. Rev. E 109, 025102] Published Mon Feb 05, 2024

Author(s): Sumit Kumar Mehta and Pranab Kumar Mondal

This work finds that the yield stress (YS) of electrically actuated viscoplastic fluids significantly influences mixing and aggregation phenomena. When shear force is applied below the YS limit, these fluids exhibit solid-like behavior due to their viscoplasticity. This is commonly observed in biological fluids like blood used in applications where rapid mixing is crucial. The local modulation of electrical forcing is achievable due to the ionic interaction between the solid and liquid phases. This leads to the observation of distinct flow structures, found to be influenced by the YS. Additionally, the likelihood of constituent particles aggregating is strongly correlated with YS.

[Phys. Rev. Fluids 9, 023301] Published Mon Feb 05, 2024

Author(s): J. Domingues Lemos and A. A. Mailybaev

Developed turbulent motion of fluid still lacks an analytical description despite more than a century of active research. Nowadays, phenomenological ideas are widely used in practical applications, such as small-scale closures for numerical simulations of turbulent flows. In the present paper, we us…

[Phys. Rev. E 109, 025101] Published Thu Feb 01, 2024

Author(s): Eric Lauga and Beverley McKeon

[Phys. Rev. Fluids 9, 010001] Published Wed Jan 31, 2024

Author(s): Pallav Kant, Mathieu Souzy, Nayoung Kim, Devaraj van der Meer, and Detlef Lohse

We present an extraordinary phenomenon that emerges from seemingly simple ingredients: a volatile droplet deposited on a highly wetting and heat-conducting warm substrate. Contrary to prevailing intuition that the deposited droplet would spread more and evaporate faster, we find that the droplet instead undergoes contraction and in addition it spontaneously and erratically moves, for substrate temperatures well below the boiling point of the liquid. We term this remarkable phenomenon “Autothermotaxis” and show that it originates from the thermal Marangoni flow in the droplet which undergoes an instability. The thermal Marangoni flow is also the reason for the contraction of the droplet.

[Phys. Rev. Fluids 9, L012001] Published Wed Jan 31, 2024

Author(s): Zhuan Ge, Teng Man, Herbert E. Huppert, Kimberly M. Hill, and Sergio Andres Galindo-Torres

Suspensions, comprising particles and fluid, play a crucial role across diverse domains, including in nature, such as submarine landslides, biological systems such as blood flows, as well as industrial materials like concrete. The rheology of these materials is a combination of both fluid and solid properties. This study introduces a dimensionless number derived from the ratio between characteristic length scales, offering a unified perspective on the rheology of dense suspensions across a spectrum from conditions where fluid-like effects dominate to regimes influenced by inertial forces. The derivation contained herein is strict, offering significant physical insight into these systems.

[Phys. Rev. Fluids 9, L012302] Published Tue Jan 30, 2024

Author(s): Shailendra Kumar Yadav, Ganesh Subramanian, and V. Shankar

The recently discovered elastic center-mode instability in plane-Poiseuille flow is shown to be present even in base flows devoid of centerline symmetry. This is illustrated using the Couette-Poiseuille family of asymmetric velocity profiles, wherein the instability is present when the maximum of the base flow is present within the channel domain. The predicted instability is potentially relevant to viscoelastic flows in the Taylor-Dean, shallow-cavity, and slider-bearing configurations.

[Phys. Rev. Fluids 9, 013301] Published Mon Jan 29, 2024

Author(s): Donato Variale, Enza Parente, Jean Christophe Robinet, and Stefania Cherubini

This work aims at studying the modal and nonmodal stability of stably stratified turbulent channel flow, assessing the influence of stratification at fixed friction Reynolds number. When increasing the stratification, the energy gain for streamwise-independent perturbations increases by two orders of magnitude, and the spanwise wavenumber for which the energy gain peaks reaches values comparable to those reported in the direct numerical simulations. Moreover, for nonzero values of the streamwise and spanwise wavenumbers, α and β, the energy gain curve has two peaks, one for shorter target times and α>β, leading to a center-channel temperature peak, and another for α<β at larger target times.

[Phys. Rev. Fluids 9, 013904] Published Mon Jan 29, 2024

Author(s): Hannes Holey, Peter Gumbsch, and Lars Pastewka

In this work we compare long wavelength fluctuations in nanoconfined simple fluids from molecular dynamics simulations with continuum descriptions. Quasi-two-dimensional descriptions of these confined fluids give rise to attenuation behavior of hydrodynamic fluctuations distinct from the bulk. Interactions with the walls introduce additional dissipation and can be related to wall slip and an anomalous dispersion relation for sound.

[Phys. Rev. Fluids 9, 014203] Published Mon Jan 29, 2024

Author(s): Caroline Braud, Bérengère Podvin, and Julien Deparday

Understanding the flow physics near stall at high chord-based Reynolds numbers (> 106) remains a challenge for both experimental and numerical approaches. Generally statistical bi-dimensionality of the flow is assumed a priori. In the present study, the wall pressure at two chords provides a description of the flow evolution with the angle of incidence. Our results indicate that flow separation at high Reynolds numbers is an inherently local, three-dimensional and unsteady process that occurs in a continuous manner. However, as it can be represented with mainly two proper orthogonal decomposition modes, our results also suggest that a low-order approach may offer a viable modeling route.

[Phys. Rev. Fluids 9, 014605] Published Fri Jan 26, 2024

Author(s): Dimitrios Angelis, Filippos Sofos, and Theodoros E. Karakasidis

The viscosity and thermal conductivity coefficients of the Lennard-Jones fluid are extracted through symbolic regression (SR) techniques from data derived from simulations at the atomic scale. This data-oriented approach provides closed form relations that achieve fine accuracy when compared to well…

[Phys. Rev. E 109, 015105] Published Thu Jan 25, 2024

Author(s): Hanliang Guo, Yi Man, and Hai Zhu

Locomotion is a combination of translation and rotation. With suitable boundary conditions, rotation can induce translation. The induced translations are more intriguing when multiple objects are rotating together. In this paper, we study theoretically the hydrodynamic bound states of two active cylinders rotating inside cylindrical confinement filled with viscous fluid. We find that the active cylinder pair can fall into four distinct non-trivial hydrodynamic bound states depending on their initial positions. Our findings may be helpful in understanding bacterial flagella rotating within a confining geometry.

[Phys. Rev. Fluids 9, 014102] Published Thu Jan 25, 2024

Author(s): Xuepeng Fu, Shixiao Fu, Mengmeng Zhang, Haojie Ren, Bing Zhao, and Yuwang Xu

An experimental apparatus for studying vortex-induced vibration (VIV) of a flexible pipe was designed and constructed in an ocean basin. A VIV test of a tensioned flexible pipe in oscillatory sheared flow (OSF) was performed based on this rotation rig. One end of the test pipe is fixed, and one end is forced to oscillate harmonically with various amplitudes and periods. The results show that VIV under OSF exhibits amplitude modulation and hysteresis phenomena. A critical Keulegan-Carpenter (KC) number is proposed to describe the occurrence of modulated VIV under OSF. The experimental results provide benchmark data for future VIV prediction research.

[Phys. Rev. Fluids 9, 014604] Published Thu Jan 25, 2024

Author(s): D. Moreno-Boza and A. Sevilla

This work investigates the linear stability of an ultrathin non-wetting liquid film on a spherical substrate in the limit of negligible inertia. The interplay between destabilizing van der Waals forces, with an exact potential description, and stabilizing surface tension gives rise to a discrete set of unstable temporal modes. Also, the performance of classical lubrication models has been assessed against the complete Stokes equations of motion.

[Phys. Rev. Fluids 9, 014004] Published Wed Jan 24, 2024

Author(s): Tso-Kang Wang and Kourosh Shoele

In this work, we demonstrated how model predictive control (MPC) can effectively manipulate a highly nonlinear foil-and-flap system to follow designated lift trajectories to sub-5% error. The surrogate model is built through a data-driven method merging fluidic and structural information which can be readily deployed to numerous fluid-structure interaction systems. The rapid optimization procedure utilized to generate the control signal can also be used for estimating ambient environmental change

[Phys. Rev. Fluids 9, 014702] Published Wed Jan 24, 2024

Author(s): Haoyang Cen, Artem Korobenko, and Qi Zhou

In this study, we explore the transition from fully developed turbulence to global intermittency in stably stratified channel flow using direct numerical simulations across varying friction Reynolds and shear Richardson numbers. We quantify intermittency by measuring the volume fraction of turbulent patches and find that intermittency can originate from either near-wall or mid-channel regions, depending on the above parameters. The study identifies a critical value of the Nusselt number (approximately 3.0) below which near-wall intermittency consistently occurs. The critical friction Richardson number for intermittency is found to be proportional to the squared Reynolds number.

[Phys. Rev. Fluids 9, 014803] Published Wed Jan 24, 2024

Author(s): Zhangyuan Wang, Dehan Yuan, Chenglong Wu, Xu Chen, Ruipeng Li, Weicheng Cui, and Dixia Fan

We develop a multitask and multifidelity Gaussian process (MMGP) model to accurately predict and optimize the multiobjective performance of a flapping foil while minimizing the cost of high-fidelity data. Through a comparison of three kernels, we have selected and applied the spectral mixture kernel…

[Phys. Rev. E 109, 015103] Published Tue Jan 23, 2024

Author(s): Írio M. Coutinho, Pedro H. A. Anjos, Rafael M. Oliveira, and José A. Miranda

The lifting Hele-Shaw cell flow commonly involves the stretching of a viscous oil droplet surrounded by air, in the confined space between two parallel plates. As the upper plate is lifted, viscous fingering instabilities emerge at the air-oil interface. Such an interfacial instability phenomenon is…

[Phys. Rev. E 109, 015104] Published Tue Jan 23, 2024

Author(s): Yunqing Liu, Qin Wu, Hanzhe Zhang, and Biao Huang

This work reveals the mechanism of cavitation-structure interaction by comparing experimental results between a stainless-steel hydrofoil and a flexible hydrofoil, encompassing hydrodynamic loads, cavitation structures, vibrations, and deformations. The hydrodynamic load induces nose-up twisting deformation, which subsequently increases the angle of attack, promoting cavitation inception. Additionally, the dynamics of cloud cavities induced by the shock wave mechanism are clarified based on high-speed images.

[Phys. Rev. Fluids 9, 014304] Published Tue Jan 23, 2024