Latest papers in fluid mechanics

Author(s): Tianyi Bai, Cheng Cheng, and Lin Fu

This work explores the streamwise inclination angle of attached eddies in both the streamwise velocity and temperature fields using direct numerical simulations of turbulent channel flows. Though it has been well studied in incompressible flows, scarce work exists in compressible flows. A high statistical similarity is found between the velocity and temperature fluctuations. The increasing trend of the inclination angle with Reynolds numbers observed in incompressible flows remains. On the contrary, the current database shows a minor Mach-number effect on it. These conclusions could serve as references for extending the attached eddy model from incompressible to compressible flows.

[Phys. Rev. Fluids 9, 034611] Published Fri Mar 29, 2024

Author(s): Johann Quenta and Desiderio A. Vasquez

Chemical reaction fronts separate regions of reacted and unreacted substances as they propagate in liquids. These fronts may induce density gradients due to different chemical compositions and temperatures across the front. In this paper, we investigate buoyancy-induced convection driven by both typ…

[Phys. Rev. E 109, 035104] Published Thu Mar 28, 2024

Author(s): Xueqing Zhang, Jeremy D. Newton, Serhiy Yarusevych, and Sean D. Peterson

Liquid droplets depinning due to shear flow aerodynamic loading is relevant to a range of engineering applications. Factors influencing depinning include droplet volume and submergence, shear flow velocity profile and acceleration, and surface wettability. A series of experiments are performed to assess the critical depinning velocity of liquid droplets subjected to an accelerating (i) laminar boundary layer, and (ii) slot jet at varying impingement angles. Critical depinning velocity, cast into a nondimensional critical Weber number, is found to be strongly related to a newly introduced volumetric shape factor, which encapsulates droplet shape and related aspects of substrate wettability.

[Phys. Rev. Fluids 9, 034004] Published Thu Mar 28, 2024

Author(s): T. Desclaux, L. Santana, I. Verdeille, P. Duru, P. Joseph, M. Delarue, and O. Liot

Bioclogging, the clogging of pores with living particles, is a complex process that involves various coupled mechanisms such as hydrodynamics, particle deformability, and polydispersity. This article aims to study a yeast clog’s permeability in a microfluidic device. We can finely measure the clog’s permeability for different hydrodynamic forcing using an original and precise on-chip flow rate meter. It reveals that yeast clog’s permeability decreases when the applied pressure increases, with saturation at high pressure. A semi-empirical model based on a double-porosity structure accurately captures the experimental observations.

[Phys. Rev. Fluids 9, 034202] Published Thu Mar 28, 2024

Author(s): Ghansham Rajendrasingh Chandel, Vishal Sankar Sivasankar, and Siddhartha Das

Active drops through active stresses alter drop evaporation dynamics, puncture evaporating drops, and induce an inside-out evaporation. For an active drop with vortex defect, activity can extend contractile drop evaporation lifetimes by 50% and can accelerate extensile drop evaporation by 33%. Non-intuitive deposition patterns emerge due to evaporation induced fluid flows where the fluid is dragged towards both outer and newly formed inner contact lines. Potential applications of such active drop evaporation include enhanced drop longevity in biological contexts and customizable thin film deposits.

[Phys. Rev. Fluids 9, 033603] Published Wed Mar 27, 2024

Author(s): Théophile Gaichies, Anniina Salonen, Arnaud Antkowiak, and Emmanuelle Rio

The base of a jet impinging on an ultrapure water bath is studied experimentally. At the impact point, a train of capillary waves develops along the jet. A striking observation is the existence of an effective nonzero water/water contact angle between the jet and the meniscus. The rationalization of this finite contact angle requires a full description of the shape of the interface. By doing an analytical matching between the meniscus and the jet, we show that the capillary waves can be considered as reflected waves present to ensure pressure continuity. It is finally shown that the value of the apparent contact angle is fixed by energy minimization.

[Phys. Rev. Fluids 9, 034003] Published Wed Mar 27, 2024

Author(s): Jungyun Kim and S. Balachandar

The present work addresses the effect of non-zero volume fraction in predicting the self-induced velocity of particles in an Euler-Lagrange (EL) simulation. Hundreds of EL simulations of flow over a random distribution of stationary particles, covering a range of Reynolds number and volume fraction, are performed to calculate the undisturbed flow and the self-induced velocities of particles in the presence of neighbors. The most significant finding is that the self-induced correction procedure of an isolated particle can be applied even at finite volume fraction, with a simple volume fraction dependent modification. However, the perturbation induced by neighbors often has a much larger effect.

[Phys. Rev. Fluids 9, 034306] Published Wed Mar 27, 2024

Author(s): Jenny Dingwall and John R. Taylor

We address the long-standing mystery surrounding the rotational bias of convective vortices in the atmosphere (dust devils) and the ocean. We investigate the bias using large-eddy simulations of free convection configured for the ocean, but the idealization of our simulations makes the results more broadly relevant to a wide range of flows. We propose a theory that the addition of many small convective vortices, each of which exhibit a small bias, leads to a much more significant bias for large convective vortices. We apply this new theory to typical convective conditions in the ocean and the terrestrial and Martian atmospheres.

[Phys. Rev. Fluids 9, 033503] Published Tue Mar 26, 2024

Author(s): Daniel B. Shaw and Luc Deike

A bursting bubble’s production of film drops - liquid from the bubble’s cap - is experimentally measured as a function of salinity, temperature, surfactant concentration, and viscosity. Existing theories for the film drainage rate and number of film drops are shown to be robustly consistent with the experimental results, but the lifetime of a bubble across various conditions remains poorly described by existing scalings. The reported relationships describing the importance of various physico-chemical variables on ocean spray emissions are of particular significance to the atmospheric and ocean science community as sea spray aerosols impact radiative transfer and cloud seeding.

[Phys. Rev. Fluids 9, 033602] Published Tue Mar 26, 2024

Author(s): Jiachen Zhao, Zhongzheng Wang, and Emilie Sauret

This study numerically and theoretically investigates the control of viscous fingering using a transverse electric field. Viscous fingering can be delayed in the presence of an electric field due to the electrical force distribution along the fluid interface and completely suppressed when the electric field strength exceeds a certain value. A non-dimensional parameter ϕ is defined based on the force balance, which shows good capability for predicting the transition from an unstable viscous fingering to stable displacement under various fluid properties and flow conditions.

[Phys. Rev. Fluids 9, 033701] Published Tue Mar 26, 2024

Author(s): A. Barrero-Gil and A. Velazquez

This letter revisits the problem of the existence of a universal Strouhal number in the separated flow past a stationary bluff body. Theoretical considerations grounded in flow kinetics yield a concise mathematical expression. The resultant model anticipates a universal Strouhal number equal to 1/2π≈0.159, aligning closely with experimental finding. Furthermore, the model has been expanded to forecast the Strouhal – Reynolds relationship in the supercritical regime, demonstrating a universal nature as it relies solely on critical Strouhal and Reynolds numbers. The circular, square, and triangular cross-section shapes have been used for validation purposes.

[Phys. Rev. Fluids 9, L032701] Published Tue Mar 26, 2024

Author(s): I. V. Kolokolov, V. V. Lebedev, and V. M. Parfenyev

We analytically examine fluctuations of vorticity excited by an external random force in two-dimensional fluid. We develop the perturbation theory enabling one to calculate nonlinear corrections to correlation functions of the flow fluctuations found in the linear approximation. We calculate the cor…

[Phys. Rev. E 109, 035103] Published Mon Mar 25, 2024

Author(s): P. D. Ravazzoli, A. G. González, and J. A. Diez

Liquid bridges are present in different four-phase systems, like the one studied here, which is formed by a liquid connecting a horizontal solid substrate with a gas phase while surrounded by another immiscible liquid. We obtain the equilibrium solutions by treating each interface as a simple curve with axial symmetry and constant curvature, and satisfying the boundary conditions given by Neumann’s and Young’s laws. Therefore, the final equilibrium solution is formed by a union of a spherical cap, a catenoid, and portions of onduloids or nodoids. We find that the γ-angle is the control parameter of the problem, as it defines the existence and shape of the final equilibrium solution.

[Phys. Rev. Fluids 9, 033601] Published Mon Mar 25, 2024

Author(s): Ashish Mishra, George Mamatsashvili, and Frank Stefani

Magnetorotational instability (MRI) is responsible for angular momentum transport in astrophysical disks. However, its definitive experimental confirmation is still missing. The upcoming DRESDYN-MRI experiments using a liquid sodium Taylor-Couette flow are a new effort to detect MRI. In preparation for this, here we study the dynamics of nonaxisymmetric MRI via simulations for the DRESDYN-MRI device. It is shown that nonaxisymmetric modes are important for large Re≳4×104 and relevant in these experiments with Re≳106. These modes are, however, of nonmagnetic nature, which grow and form a turbulent boundary layer near the cylinders, while axisymmetric MRI dominates in the bulk flow.

[Phys. Rev. Fluids 9, 033904] Published Mon Mar 25, 2024

Author(s): Yu Sun, Yi-Chao Xie, Jin-Xiao Xie, Jin-Qiang Zhong, Jianwei Zhang, and Ke-Qing Xia

A physically motivated low-dimensional model describes properly the interaction of two vertically-aligned large-scale circulations (LSC) in two-layer turbulent convection, and predicts their preferred flow states of thermal and viscous coupling. The model reveals that flow reversals can be achieved when turbulent fluctuations drive the LSC azimuthal diffusion into a flow state such that the two LSC planes are orthogonal to each other, the strength of the LSC in the high Rayleigh number fluid layer then reduces to zero deterministically. The model provides satisfactory interpretation for the high occurrence frequency of flow reversals observed in two-layer turbulent convection.

[Phys. Rev. Fluids 9, 033501] Published Fri Mar 22, 2024

Author(s): Hailong Huang, Yin Wang, Wei Xu, Xiaozhou He, and Penger Tong

In this work, we conducted a systematic experimental study of turbulent two-layer convection in an upright cylinder, as illustrated. From the measured mean temperature and temperature variance profiles, we find a unique twin-boundary-layer structure across the liquid interface with one of the twin boundary layers (BLs) on each side of the interface. The functional form of the measured mean temperature and temperature variance profiles is well described by the equations for a BL attaching to a solid conducting plate, so long as a thermal slip length is introduced to account for the convective heat flux passing through the liquid interface.

[Phys. Rev. Fluids 9, 033502] Published Fri Mar 22, 2024

Author(s): Pablo Ouro, Hannah Mullings, Aristos Christou, Samuel Draycott, and Tim Stallard

Understanding of the influence of waves on a tidal turbine wake in a turbulent channel flow is developed using large eddy simulations with modeling of the air-water interphase deformation. For wavelengths between two- and sixteen-times channel depth, the rate of wake recovery is faster than in the absence of waves with only small differences in turbine mean loading. The smallest wavelengths cause fastest wake recovery, and hence shortest wake length. This is due to enhanced vertical and transverse components of convection and turbulent transport of mean kinetic energy. Advection of helical tip vortices shed by the turbine blades is impacted by vertical and streamwise wave kinematics.

[Phys. Rev. Fluids 9, 034608] Published Fri Mar 22, 2024

Author(s): Xi Chen, Peng-Yu Duan, and Jianchao He

What would be the ultimate statistical invariance for wall turbulence? In 3D flows, whether turbulent fluctuations are bounded or unbounded for a series of quantities when the Reynolds number (Re) tends to infinity, is debated. Here, we focus on 2D wall turbulence and find that fluctuations in wall units such as root mean square of wall pressure, wall shear stress intensity, streamwise velocity fluctuation, etc., all exhibit a distinct Re1/3 scaling law. This scaling indicates an unbounded behavior for 2D flows due to the inverse energy cascade, which sheds light on the asymptotical behavior of 3D flows that fluctuations might be bounded because of the forward energy cascade.

[Phys. Rev. Fluids 9, 034609] Published Fri Mar 22, 2024

Author(s): Giorgio Krstulovic and Sergey Nazarenko

The development of singular structures and the path to turbulence in fluids is a fundamental problem that has puzzled researchers for a long time. In this work, we study numerically the evolution of a large-scale initial condition under the hyperviscous incompressible Navier-Stoke equations. Our observations revealed the emergence of shrinking vortex pancakes, which lead to vortex ribs and, eventually, vortex ropes, as depicted in the figure. Eventually, a fully developed turbulent state was achieved prior to its viscous decay.

[Phys. Rev. Fluids 9, 034610] Published Fri Mar 22, 2024

Author(s): Nabil M. Khalifa and Haithem E. Taha

Vortices are found everywhere around us at every scale. Current models describing vortices are mainly kinematics-based, in which the resulting dynamics are limiting in their nature. Relying on these models, one can predict vortices response for a prescribed initial condition but cannot study their response under generic conditions and external disturbances. That is because current models are a well devised formulation. However, we propose a model from first-variational principles relying on the Principle of Least Action, and not only was it able to predict the vortices response in a generic sense, but also it can be extended to include varying strength vortices or any dynamical constraints.

[Phys. Rev. Fluids 9, 034701] Published Fri Mar 22, 2024