Latest papers in fluid mechanics

Point torque representations of ciliary flows

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

Author(s): Siluvai Antony Selvan, Peter W. Duck, Draga Pihler-Puzović, and Douglas R. Brumley

The beating of cilia and flagella has fascinated biologists and physicists alike for decades. Previous mathematical models designed to capture the corresponding flow fields are typically either highly simplified and do not resolve all lengths scales or are computationally demanding and cannot be easily generalized to larger arrays of cilia. This paper develops an alternative method which uses point torques to represent the cilia and captures the near- and far-field characteristics in an efficient and accurate manner. These singularity solutions can be used to accurately calculate the collective flows and transport properties of larger ciliary arrays.


[Phys. Rev. Fluids 8, 123103] Published Tue Dec 12, 2023

From nearly homogeneous to core-peaking suspensions: Insight in suspension pipe flows using MRI and DNS

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

Author(s): Willian Hogendoorn, Wim-Paul Breugem, David Frank, Martin Bruschewski, Sven Grundmann, and Christian Poelma

Semi-dilute to dense particle-laden inertial pipe flows are studied using magnetic resonance imaging in conjunction with direct numerical simulations. In general, both methods show an excellent agreement for both the time-averaged velocity and concentration profiles. Different flow regimes are identified based on the experimental and numerical data. For higher solid volume fractions a core-peaking concentration distribution is found that explains the observed drag decrease relative to the drag expected for a uniform concentration distribution.


[Phys. Rev. Fluids 8, 124302] Published Tue Dec 12, 2023

Inertial migration of spherical and oblate particles in a triangular microchannel

Physical Review E - Mon, 12/11/2023 - 10:00

Author(s): Junqi Xiong, Xuechao Liu, Huiyong Feng, and Haibo Huang

The. inertial migration of both spherical and oblate particles within an equilateral triangular channel is studied numerically. Our study primarily focuses on the effects of fluid inertia, quantified by the Reynolds number (Re) and particle size (β). Our observations reveal two distinct equilibrium …


[Phys. Rev. E 108, 065105] Published Mon Dec 11, 2023

Modeling flow of Carreau fluids in porous media

Physical Review E - Mon, 12/11/2023 - 10:00

Author(s): Christopher A. Bowers and Cass T. Miller

Carreau fluids occur routinely in porous medium systems for a range of applications, and the dependence of the viscosity for such fluids on the rate of strain tensor poses challenges to modeling at an averaged macroscale. Traditional approaches for macroscale modeling such flows have relied upon exp…


[Phys. Rev. E 108, 065106] Published Mon Dec 11, 2023

Mean streaming and the onset of turbulence in the reciprocating flow in a double bifurcation airway model: Insights for high-frequency ventilation

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Chinthaka Jacob, David G. Tingay, and Justin S. Leontini

This paper reports on a reciprocating flow through a double bifurcation geometry to quantify the potential gas transport in flows similar to those in the human airway during high-frequency ventilation. The roles of nonlinear mean streaming and turbulent diffusion are investigated in appropriate clinical conditions and their dependence on both the upstream and downstream conditions are manifested. We report turbulent bursts occur in the first three generations of the airway when the instantaneous flow velocity exceeds a critical value. Results highlight the importance of considering a model geometry with appropriate complexity for physiological flows.


[Phys. Rev. Fluids 8, 123102] Published Mon Dec 11, 2023

Premixed flame stability under shear-enhanced diffusion: Effect of the flow direction

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Joel Daou and Prabakaran Rajamanickam

In the presence of shear-enhanced diffusion (Taylor dispersion), flame propagation is effectively anisotropic. The paper clarifies the influence of the direction of a shear flow relative to the direction of propagation on the diffusional-thermal instabilities of premixed flames. Interestingly, the cellular flame instability can now be encountered in mixtures with Lewis numbers larger than one.


[Phys. Rev. Fluids 8, 123202] Published Mon Dec 11, 2023

Numerical investigation of quasistatic magnetoconvection with an imposed horizontal magnetic field

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Michael A. Calkins, Talal AlRefae, Angel Hernandez, Ming Yan, and Stefano Maffei

Buoyancy-driven flow of an electrically conducting fluid occurs in planets, stars and industrial applications. Here we use simulations of Rayleigh-Bénard convection with an imposed horizontal magnetic field and stress-free mechanical boundary conditions as a simplified model for understanding such systems. As the buoyancy forcing and magnetic field strength are increased we find a sequence of bifurcations, ranging from steady two-dimensional convection cells to three-dimensional anisotropic convective turbulence. Large scale mean flows become dominant as the parameters are made more extreme.


[Phys. Rev. Fluids 8, 123501] Published Mon Dec 11, 2023

Biglobal analysis of baroclinic instability in a current-undercurrent oceanic system

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Xianliang Chen, Jianping Gan, and James C. McWilliams

We study the dynamics of a mesoscale current-undercurrent system motivated from the multilayer circulations in the Western North Pacific, attempting to further understand the dynamic origin of the Luzon Undercurrent. We adopt the so-called biglobal analysis, which can deal with realistic basic flows of continuously nonuniform vertical shear and strong horizontal variation. The high vertical shear between the upper and lower currents, and that near the vertical boundaries give rise to two branches of unstable modes of distinct dynamical features. The interplay between baroclinic and barotropic instabilities, as well as the coupling ageostrophic and viscous/diffusive motions are revealed.


[Phys. Rev. Fluids 8, 123801] Published Mon Dec 11, 2023

Dissolution regimes of a horizontal channel in a gravity field

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Wei Guo, Ran Hu, Chen-Xing Zhou, Zhibing Yang, and Yi-Feng Chen

We fabricate a soluble microfluidic channel within a micro-PIV-based imaging system to explore the pore-scale dissolution dynamics in a gravity field. We find that the evolution of eddies induced by buoyancy-driven convection within the flow-dissolution system governs the dissolution rate and the dissolution regimes. This research enhances our comprehension of the interplay between buoyancy-driven convection and forced convection in etching the solid surface.


[Phys. Rev. Fluids 8, 123902] Published Mon Dec 11, 2023

Systematic approach for modeling a nonlocal eddy diffusivity

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Jessie Liu, Hannah H. Williams, and Ali Mani

Prior studies have shown that the eddy diffusivities governing mean passive scalar transport can be nonlocal in space and time. However, nonlocal eddy diffusivities are often cost prohibitive to compute and difficult to implement in reduced-order models. This work proposes a systematic and cost-effective approach for quantifying and modeling nonlocal eddy diffusivities.


[Phys. Rev. Fluids 8, 124501] Published Mon Dec 11, 2023

Reynolds-number effects on the outer region of adverse-pressure-gradient turbulent boundary layers

Physical Review Fluids - Mon, 12/11/2023 - 10:00

Author(s): Rahul Deshpande, Aron van den Bogaard, Ricardo Vinuesa, Luka Lindić, and Ivan Marusic

Reynolds number (Re) effects are studied in the outer region of moderate adverse-pressure-gradient (APG) turbulent boundary layers (TBLs). This study finds that the small scale (viscous) energy in an APG TBL at near-equilibrium conditions reduces with increasing friction Re. The origin of this trend is traced back to the production of turbulent kinetic energy in an APG TBL, the small scale contribution to which is also found to decrease with Re in the outer region. The results emphasize that new scaling arguments and spatial-resolution corrections should be tested rigorously across a broad range of Re, particularly for pressure gradient TBLs.


[Phys. Rev. Fluids 8, 124604] Published Mon Dec 11, 2023

Tensor network reduced order models for wall-bounded flows

Physical Review Fluids - Fri, 12/08/2023 - 10:00

Author(s): Martin Kiffner and Dieter Jaksch

We introduce a quantum inspired and widely applicable tensor network-based framework for developing reduced order models describing wall-bounded fluid flows. For the examples of the lid-driven and doubly-driven cavities, we find that our method only uses a small fraction of the number of variables parameterizing the solution compared to direct numerical simulation and can improve its runtime by an order of magnitude on comparable hardware. Our work provides a novel path towards efficient high-precision simulations of the Navier-Stokes equation at high Reynolds numbers.


[Phys. Rev. Fluids 8, 124101] Published Fri Dec 08, 2023

Size of heterogeneous deformations in sheared granular flows

Physical Review Fluids - Fri, 12/08/2023 - 10:00

Author(s): Parisa Shekari, Benjy Marks, and Pierre Rognon

Granular flows exhibit kinematic patterns reminiscent of turbulence. In discrete element method simulations, we measure the characteristic size of these patterns and relate it to the size of a representative element volume (REV). We find that this size increases and diverges close to jamming. Such large REVs may be the root cause of nonlocal behaviors and finite size effects observed at the continuum level.


[Phys. Rev. Fluids 8, 124301] Published Fri Dec 08, 2023

$H$-theorem and boundary conditions for two-temperature model: Application to wave propagation and heat transfer in polyatomic gases

Physical Review E - Thu, 12/07/2023 - 10:00

Author(s): Anil Kumar and Anirudh Singh Rana

Polyatomic gases find numerous applications across various scientific and technological fields, necessitating a quantitative understanding of their behavior in nonequilibrium conditions. In this study, we investigate the behavior of rarefied polyatomic gases, particularly focusing on heat transfer a…


[Phys. Rev. E 108, 065103] Published Thu Dec 07, 2023

Dynamics of a silicone oil drop submerged in a stratified ethanol-water bath

Physical Review E - Thu, 12/07/2023 - 10:00

Author(s): Miguel A. Herrada, José M. Montanero, and Luis Carrión

We analyze numerically the Marangoni flow around an immiscible droplet submerged in a stably stratified mixture of ethanol and water. The linear stability analysis shows that the base flow undergoes a supercritical Hopf bifurcation that leads to oscillations. The theoretical prediction for the criti…


[Phys. Rev. E 108, 065104] Published Thu Dec 07, 2023

Dynamic lift enhancement mechanism of dragonfly wing model by vortex-corrugation interaction

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): Yusuke Fujita and Makoto Iima

Dragonfly wings, with their unique corrugated structure, may achieve superior aerodynamic performance in specific flight conditions, although these conditions are not yet fully understood. This led us to investigate the vortex dynamics and lift generation as a corrugated wing transitions from a stationary state to translational motion. The results reveal that suppression of secondary vortices generated on the wing significantly improves the overall performance of corrugated wings. This advances our understanding of flight dynamics and can also contribute to applications in engineering and biomimicry.


[Phys. Rev. Fluids 8, 123101] Published Thu Dec 07, 2023

Towards a constitutive relation for emulsions exhibiting a yield stress

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): H. V. M Kibbelaar, A. Deblais, G. Briand, Y. Hendrix, A. Gaillard, K. P. Velikov, M. M. Denn, and D. Bonn

Many materials encountered around us in daily life are yield stress materials, which behave solid-like for small applied stresses, but start to flow when the applied stress exceeds a threshold. The shear viscosity of these materials is relatively well understood. However, this is far from a complete and satisfactory description of the mechanical response, and most flows are more complicated. A coherent picture for general flows is still lacking.


[Phys. Rev. Fluids 8, 123301] Published Thu Dec 07, 2023

Experiments on the unsteady massive separation over an aerofoil

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): S. Mohamed Aniffa and Alakesh Ch. Mandal

Instantaneous flow fields over a NACA 0012 aerofoil at the stall and post-stall angles of attack have been measured using the time-resolved particle image velocimetry technique. The time sequence of the measured data reveals that the massive separation over the upper surface of the aerofoil is intermittent in nature. This intermittent massive separation is due to the interchange of instability, that is, from a convective to an absolute instability and from an absolute to a convective instability. A physical mechanism for this intermittent massive separation has also been proposed.


[Phys. Rev. Fluids 8, 123901] Published Thu Dec 07, 2023

Exploring regular and turbulent flow states in active nematic channel flow via Exact Coherent Structures and their invariant manifolds

Physical Review Fluids - Thu, 12/07/2023 - 10:00

Author(s): Caleb G. Wagner, Rumayel H. Pallock, Jae Sung Park, Michael M. Norton, and Piyush Grover

Active fluids operating at negligible Reynolds numbers can exhibit spontaneous coherent motion, dynamical vortex patterns, and mesoscale turbulence. We employ tools from nonlinear dynamical systems theory to uncover the global phase space of two-dimensional active nematic channel flow. We compute several Exact Coherent Structures (ECSs), which are exact solutions of the physical dynamics with distinct and regular spatiotemporal structure; examples include unstable equilibria, periodic orbits, and traveling waves. We provide numerical evidence to show that this collection of ECSs and their invariant manifolds act as an organizing template for the complicated spatiotemporal motion of the active fluid.


[Phys. Rev. Fluids 8, 124401] Published Thu Dec 07, 2023

Viscous free-surface cusps: Local solution

Physical Review Fluids - Wed, 12/06/2023 - 10:00

Author(s): J. Eggers

In the image, the free surface between a liquid and air is deformed into a sharp cusp by the rapid rotation of the cylinder on the left. We show that such a structure is a generic feature of viscous flow, and study its properties. This is important, since air can enter the fluid through the cusp’s tip, and thus become entrained into the interior of the fluid.


[Phys. Rev. Fluids 8, 124001] Published Wed Dec 06, 2023

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