New Papers in Fluid Mechanics

Dynamics of particle-laden turbulent suspensions: Effect of particle roughness

Physical Review Fluids - Mon, 06/10/2024 - 11:00

Author(s): S. Ghosh, P. S. Goswami, and V. Kumaran

Fluctuating force, fluctuating torque simulations accurately predict the particle dynamics in particle-laden turbulent flows.


[Phys. Rev. Fluids 9, 064303] Published Mon Jun 10, 2024

Two regimes of dilute turbulent settling suspensions under shear

Physical Review Fluids - Mon, 06/10/2024 - 11:00

Author(s): Jake Langham and Andrew J. Hogg

Clouds of fine particles held aloft by turbulent fluctuations are widespread in natural flows. Although these suspensions are known to inhibit the turbulence supporting them, this effect remains unstudied in many of the most basic settings, such as shear-driven flows. We trace part of the laminar-turbulent boundary for particle-laden plane Couette flow and find unexpectedly that turbulence suppression depends non-monotonically on particle settling velocity. On either side of laminar flow lie two very different states: near-homogeneous weakly stratified turbulence and a patchier regime where sediment is intermittently lifted into suspension from a highly suppressed boundary layer.


[Phys. Rev. Fluids 9, L062602] Published Mon Jun 10, 2024

From cavitation to astrophysics: Explicit solution of the spherical collapse equation

Physical Review E - Fri, 06/07/2024 - 11:00

Author(s): Danail Obreschkow

Differential equations of the form R̈=−kRγ, with a positive constant k and real parameter γ, are fundamental in describing phenomena such as the spherical gravitational collapse (γ=−2), the implosion of cavitation bubbles (γ=−4), and the orbital decay in binary black holes (γ=−7). While explicit ele…


[Phys. Rev. E 109, 065102] Published Fri Jun 07, 2024

Numerical investigation on particle inertial migration in circular Poiseuille flow with thermal convection

Physical Review Fluids - Fri, 06/07/2024 - 11:00

Author(s): Jingwen Fu, Wenwei Liu, Xing Jin, and Yun Huang

A numerical study on the inertial migration of particle suspension in a circular pipe with thermal effect is performed by means of the Lattice Boltzmann method coupled with the discrete element method (LBM-DEM). The particle position and heat transfer for single particle as well as particle suspensions are discussed. Then, we extend the work to varied temperature conditions. It is shown that the variation of the circumferential equilibrium position can be well regressed by the Richardson number. A nonmonotonic variation of the radial equilibrium position as well as the Nusselt number is discovered, which is attributed to the particle crowding effect.


[Phys. Rev. Fluids 9, 064302] Published Fri Jun 07, 2024

Statistical theory of passive scalar turbulence within the viscous-convective range

Physical Review Fluids - Fri, 06/07/2024 - 11:00

Author(s): Taketo Ariki

Passive scalar turbulence in the viscous-convective range is investigated via a self-consistent closure theory. Without relying on any empirical parameter the theory successfully explained the scalar-variance spectrum proportional to the inverse wavenumber k−1 from the scalar’s deformation timescale dominated by the Kolmogorov-scale eddy, which agrees with the physical viewpoint of Batchelor (1959). High Schmidt number (Sc) calculations up to Sc=100000 suggest that a clear Batchelor spectrum may appear in kη≳1 for Sc≳10000 where η is the Kolmogorov length.


[Phys. Rev. Fluids 9, 064603] Published Fri Jun 07, 2024

Predicting the slowly converging dynamics of asymmetric vortex wakes

Physical Review Fluids - Fri, 06/07/2024 - 11:00

Author(s): Qiang Zhong and Daniel B. Quinn

Hydrofoils with symmetric oscillations can generate asymmetric vortex wakes. This surprising asymmetry has been widely reproduced, but a simple metric to predict its onset has remained elusive. Here, using a combination of vortex modeling and water channel experiments, we show that vortex wake deflection is well-predicted by the “relative dipole angle”. In addition to offering a predictive physics-based metric, our results show that a hydrofoil’s wake can converge much more slowly than previously thought (200+ oscillation cycles), and that the wake’s asymmetry is more than a memory of the hydrofoil’s initial condition - it is an instability inherent to the vortex street.


[Phys. Rev. Fluids 9, 064702] Published Fri Jun 07, 2024

Tunable transport in bidisperse porous materials with vascular structure

Physical Review Fluids - Thu, 06/06/2024 - 11:00

Author(s): Olivier Vincent, Théo Tassin, Erik J. Huber, and Abraham D. Stroock

We study water transport in bi-disperse porous structures inspired by xylem tissue in vascular plants (arrays of microchannels interconnected by a nanoporous layer). With various experiments (high pressure-driven flow, spontaneous imbibition, transpiration-driven flow at negative pressure), we show that transport rates can be tuned by varying the shape of the microchannels. Even with a fixed shape, spontaneous imbibition behaves very differently depending on sample preparation (air-filled vs. evacuated), because of a dramatic change of transport mechanism in the microchannels. We provide analytical (effective medium) approaches and numerical simulations to rationalize these observations.


[Phys. Rev. Fluids 9, 064202] Published Thu Jun 06, 2024

Opposition flow control for reducing skin-friction drag of a turbulent boundary layer

Physical Review Fluids - Thu, 06/06/2024 - 11:00

Author(s): Giulio Dacome, Robin Mörsch, Marios Kotsonis, and Woutijn J. Baars

With the goal of performing opposition control of large-scale drag-producing turbulence structures, we present a successful control strategy that attenuates large-scale velocity fluctuations in a turbulent boundary layer. Our control architecture consists of a wall-embedded sensor that feeds information to a real-time controller, which selectively operates a jet actuator. We quantify the performance of this single-input/single-output system with spectral statistics and direct skin-friction measurements. Additionally, we link the changes in skin-friction drag to changes in the statistical integral quantities to gauge the correlation between control output and skin-friction variation.


[Phys. Rev. Fluids 9, 064602] Published Thu Jun 06, 2024

Dynamo action driven by precessional turbulence

Physical Review E - Wed, 06/05/2024 - 11:00

Author(s): Vivaswat Kumar, Federico Pizzi, George Mamatsashvili, André Giesecke, Frank Stefani, and Adrian J. Barker

We reveal and analyze an efficient magnetic dynamo action due to precession-driven hydrodynamic turbulence in the local model of a precessional flow, focusing on the kinematic stage of this dynamo. The growth rate of the magnetic field monotonically increases with the Poincaré number Po, characteriz…


[Phys. Rev. E 109, 065101] Published Wed Jun 05, 2024

From low-frequency oscillations to Markovian bistable stall dynamics

Physical Review Fluids - Wed, 06/05/2024 - 11:00

Author(s): Ivan Kharsansky Atallah, Luc Pastur, Romain Monchaux, and Laurent Zimmer

An experimental study is conducted on a thin symmetric airfoil at stall. Below a critical Reynolds number, the flow exhibits low-frequency oscillations (LFOs) characterized by a broadband peak in the aerodynamic force spectrum. Beyond this threshold, the LFOs are replaced by intermittent random switches between two states of either high or low lift (attached or detached flow). The states are explored randomly in time for a fixed angle of attack, contrary to the classical hysteresis often observed in airfoil flows at stall, where both states are absorbing. We model this using a continuous Markov chain and extreme value theory, a framework that can determine the system bifurcation points.


[Phys. Rev. Fluids 9, 063902] Published Wed Jun 05, 2024

Mean and fluctuating helicity in swirling jet flows

Physical Review Fluids - Wed, 06/05/2024 - 11:00

Author(s): Rodion Stepanov, Peter Frick, Vladimir Dulin, and Dmitriy Markovich

Our experimental research demonstrates that helicity in turbulent flows undergoes a direct spectral transfer from large to small scales. Tomographic particle image velocimetry provides insights into the spatial and spectral segregation of turbulent flows with different helicity signs. We show that helicity generation and decay along the jet dramatically depends on the inflow swirl. Notably, we provide direct experimental evidence of the helicity cascade, discovering that swirls of the same sign can impart turbulent helicity of the opposite sign, challenging conventional assumptions. These findings offer valuable benchmarks for numerical simulations using different turbulent closure methods.


[Phys. Rev. Fluids 9, L062601] Published Wed Jun 05, 2024

Influence of adversarial training on super-resolution turbulence reconstruction

Physical Review Fluids - Tue, 06/04/2024 - 11:00

Author(s): Ludovico Nista, Heinz Pitsch, Christoph D. K. Schumann, Mathis Bode, Temistocle Grenga, Jonathan F. MacArt, and Antonio Attili

We compare supervised super-resolution convolutional neural networks (CNNs) against generative adversarial networks (GANs)-based architectures in the ability to reconstruct turbulent flow fields. GANs demonstrated superior in-sample performance but faced challenges with out-of-sample flows. Incorporating a partially unsupervised adversarial training step with large eddy simulation inputs and dynamic upsampling selection improved GANs’ out-of-sample robustness, capturing small-scale features and turbulence statistics better than standard supervised CNNs. The study recommends integrating discriminator-based training to enhance super-resolution CNNs’ reconstruction capabilities.


[Phys. Rev. Fluids 9, 064601] Published Tue Jun 04, 2024

Impact of rotation change on the emptying of an ideal bottle of water

Physical Review Fluids - Tue, 06/04/2024 - 11:00

Author(s): A. Caquas, L. R. Pastur, and A. Genty

Have you ever tried spinning your water bottle to empty it more quickly? This experiment, familiar to the general public, has rarely been studied in the scientific literature, which focuses mainly on the non-rotational case. We show that this popular experiment is surprisingly complex. Our study reveals the presence of three flow regimes, which have a direct impact on the efficiency of the draining process.


[Phys. Rev. Fluids 9, 064701] Published Tue Jun 04, 2024

Influence of plasticity on inertialess viscoelastic instabilities in elongational flow regimes

Physical Review Fluids - Mon, 06/03/2024 - 11:00

Author(s): V. Dzanic, C. S. From, and E. Sauret

This study explores, for the first time, the impact of plasticity on inertialess viscoelastic instabilities in strong elongational flows. Through detailed numerical simulations, it reveals how elastoviscoplastic effects induce complex and dynamic flow behaviors, leading to new flow states. Crucially, our findings reveal that plasticity can laminarize and suppress these instabilities, offering new strategies for controlling the instability mechanism.


[Phys. Rev. Fluids 9, 063301] Published Mon Jun 03, 2024

Influence of the imposed flow rate boundary condition on the flow of Bingham fluid in porous media

Physical Review Fluids - Mon, 06/03/2024 - 11:00

Author(s): Laurent Talon, Andreas Andersen Hennig, Alex Hansen, and Alberto Rosso

We consider different boundary conditions for imposing flow of yield stress fluids in porous media. In contrast to Newtonian fluids in porous media, imposing pressure or a given flow profile at the boundary leads to significantly different flow fields. In particular, we show that imposing a flow profile leads to a merging tree structure whose properties are governed by the dynamics of a directed polymer in a random medium.


[Phys. Rev. Fluids 9, 063302] Published Mon Jun 03, 2024

Three-dimensional receptivity of hypersonic sharp and blunt cones to free-stream planar waves using hierarchical input-output analysis

Physical Review Fluids - Mon, 06/03/2024 - 11:00

Author(s): David A. Cook and Joseph W. Nichols

Hypersonic boundary layers are susceptible to flow instabilities that cause laminar flow to transition to turbulence, significantly increasing aerodynamic drag and wall heating. We focus on how these instabilities are triggered by the environment by applying a control systems theory technique called “input-output analysis” that relies in part upon solving the Navier-Stokes equations in reverse, tracing instabilities back to their origins. In the complex interactions between atmospheric disturbances, shock waves created near the nose cone of a hypersonic vehicle, and boundary layer instabilities, we find two physical processes strongly connected to the bluntness of the nose cone tip.


[Phys. Rev. Fluids 9, 063901] Published Mon Jun 03, 2024

Emergence of dissipation and hysteresis from interactions among reversible, nondissipative units: The case of fluid-fluid interfaces

Physical Review Fluids - Mon, 06/03/2024 - 11:00

Author(s): Ran Holtzman, Marco Dentz, Marcel Moura, Mykyta V. Chubynsky, Ramon Planet, and Jordi Ortín

Fluid-fluid displacement is often irreversible—exhibiting hysteresis where reversal of the driving force (e.g. external pressure) does not reverse the fluids’ configuration. This irreversibility is linked to energy dissipation, a key to efficient design of engineering operations such as subsurface cleanup or energy storage. Here, we analyze (analytically, numerically, and experimentally) a novel model system that exposes a striking phenomenon: emergence of hysteresis and dissipation in a system made of individually “reversible” (non-hysteretic) entities, due to their spatial interactions mediated by interfacial tension.


[Phys. Rev. Fluids 9, 064001] Published Mon Jun 03, 2024

Dynamic coupling of rigid in-plane pore oscillations and flow through nanoporous two-dimensional membranes

Physical Review Fluids - Mon, 06/03/2024 - 11:00

Author(s): J. P. Martínez Cordeiro and N. R. Aluru

Most of the literature on flow through nanoporous two-dimensional membranes has focused on static membranes, yet various studies have shown the relevance of fluid-structure interactions – particularly dynamic coupling – on flow through nanopores. Herein, we use Molecular Dynamics (MD) simulations to study the effects of rigid in-plane harmonic pore oscillations on water flow through nanoporous graphene. First, we repurpose a used technique as a framework to isolate the physical mechanisms caused by the dynamic pore from the injected heat. We show that dynamic opening/closing of flow routes inside the pore enhances flow by increasing axial velocity and decreasing water density inside the pore.


[Phys. Rev. Fluids 9, 064201] Published Mon Jun 03, 2024

Spheres and fibers in turbulent flows at various Reynolds numbers

Physical Review Fluids - Mon, 06/03/2024 - 11:00

Author(s): Ianto Cannon, Stefano Olivieri, and Marco E. Rosti

We use immersed boundary methods to simulate finite-size spheres and fibers in turbulent flows across a range of Taylor Reynolds numbers (12.8<Reλ<442) and solid mass fractions (0≤M≤1). Both particle shapes act as a “spectral shortcut” to the flow, with fibers extending this effect further into the dissipative range. Spheres enhance dissipation in two-dimensional sheets, while fibers enhance dissipation in structures with dimension between one and two. However, the particles’ effect on the anomalous dissipation tends to vanish as Reλ→∞. These findings have implications for microplastics in oceans, volcanic ash clouds, and sandstorms.


[Phys. Rev. Fluids 9, 064301] Published Mon Jun 03, 2024

Volumetric visualization of vanishing vortices in wind turbine wakes

Physical Review Fluids - Fri, 05/31/2024 - 11:00

Author(s): Johannes N. Hillestad, Srikar Yadala, Ingrid Neunaber, Leon Li, R. Jason Hearst, and Nicholas A. Worth

The “anomalous” peaks in experimentally obtained power spectral density plots in the wake of wind turbines are investigated with time-resolved volumetric measurements. To promote early tip vortex interaction, blades with different angles-of-attack are used on the same rotor. Using an advanced volumetric technique to obtain the velocity field in the wake, the tip vortex interaction is visualized and quantified. The captured tip vortices corroborate the findings from power spectral density plots at different downstream locations that only one vortex is dominant, demonstrating that a difference in initial vortex strength can result in vortical energy being distributed at unexpected frequencies.


[Phys. Rev. Fluids 9, L052701] Published Fri May 31, 2024

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