Latest papers in fluid mechanics

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

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

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

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

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

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

Author(s): Himani Garg and Christer Fureby

Polymer solutions in the dilute regime play a significant role in industrial applications. Due to the intricate rheological properties of these highly viscoelastic fluids, especially in complex flow geometries, a thorough numerical analysis of their flow dynamics is imperative. In this research, we …

[Phys. Rev. E 109, 055108] Published Wed May 29, 2024

Author(s): T. Zemach

We investigate high-Reynolds-number polydisperse gravity currents propagating along a channel of general cross-section into a linearly stratified ambient fluid. We formulate and solve numerically the shallow water equations and present typical height and velocity profiles of the current and particle mass concentration. Two dimensionless parameters, Stratification (S) and particle buoyancy (Π), are relevant. Increasing S decreases the current velocity propagation, but as Π increases, the current propagates faster. For a specific S, Π dependence, an equilibrium occurs for a significant time and the system behaves like a system without particles propagating into the ambient of constant density.

[Phys. Rev. Fluids 9, 054105] Published Tue May 28, 2024

Author(s): Alessio Roccon, Francesco Zonta, and Alfredo Soldati

The transportation of oil through pipelines and channels is a highly energy-intensive operation, primarily due to the significant viscosity of the oil and the consequent high friction. Among the various friction reduction methods utilized in this domain, the water-lubricated approach has emerged as particularly promising. Our investigation focuses on assessing the efficacy of this technique through direct numerical simulations of turbulent channel flow. In this setup, we introduce two thin water layers near the walls, which serve to lubricate the flow of oil within the core.

[Phys. Rev. Fluids 9, 054611] Published Tue May 28, 2024

Author(s): Saini Jatin Rao, Siddhant Jain, and Saptarshi Basu

Often considered a childhood pastime, soap bubbles emerged as a captivating domain for rigorous scientific inquiry for generations. While blowing soap bubbles is familiar to everyone, the underlying physics of inflating them remains unanswered. In our investigation, we visualize the previously unexplored internal airflow experimentally, revealing a toroidal vortical flow that resembles a bound vortex ring. The air enters the bubble as a round jet, emerging from the nozzle opening and impinges on the expanding concave interior to form this toroidal vortex. We also predict several scaling laws for the inflation rate and dynamics of this confined vortical flow by varying the source pressure.

[Phys. Rev. Fluids 9, L051602] Published Tue May 28, 2024

Author(s): Loïc Chagot, Simona Migliozzi, and Panagiota Angeli

In this Letter, we explore the influence of colloids at liquid-liquid interfaces on droplet pinch-off dynamics in microfluidic devices. We uncover a significant deviation in droplet formation time compared to pure systems, similarly to surfactant-laden systems. Yet notably, colloids exert minimal impact on droplet size, indicating potential nonlinear effects. The dynamics of neck thinning without colloids agree with the classic pendant drop scaling laws, while particle presence replaces traditional viscous and inertial-viscous regimes with a single power law, suggesting an elastic behavior driven by soft particle interactions.

[Phys. Rev. Fluids 9, L052201] Published Tue May 28, 2024

Author(s): Sergiu Busuioc

This paper derives the Enskog equation in the context of orthonormal vielbein fields, allowing the use of arbitrary coordinate systems to describe spatial geometry. Additionally, an adapted coordinate system in momentum space is employed, which is connected to physical space via vielbeins. A suitable finite-difference lattice Boltzmann model is developed and validated against a direct simulation Monte Carlo particle-based method for solving the Enskog equation in curvilinear geometries. The test scenarios include cylindrical Couette and Fourier flow between coaxial cylinders, and spherical Fourier flow between concentric spheres.

[Phys. Rev. Fluids 9, 053401] Published Thu May 23, 2024

Author(s): Cheng Cheng and Lin Fu

We report a new Mach number invariant function for the mean temperature field in compressible wall turbulence. We demonstrate its validation by comparing it with the invariant functions derived in the previous studies, i.e., the semi-local-type and van-Driest-type scalings, case by case. The newly proposed temperature transformations based on the new scaling show an improvement in channel flows over adiabatic walls and supersonic/hypersonic turbulent boundary layers with cold walls. The effects of the generated high-order terms during derivation are also clarified. These findings may be revealing for the development of the near-wall model in high-speed aerodynamics.

[Phys. Rev. Fluids 9, 054610] Published Thu May 23, 2024

Author(s): I. Rubinstein and B. Zaltzman

Dendrite formation resulting from morphological instability in cathodic electrodeposition of a metal and, especially, the role that related fluid flows play, has long been of major interest to physicists. We focus on the physical mechanisms behind: (1) Underlimiting currents: Selection of electrokinetic-reactive length scale, which is the geometric average of the electric double layer width and the reaction-diffusion length defined as the ratio of cation diffusivity to electrode reaction rate; (2) Overlimiting currents: Domination of emerging electroconvective flow, selecting the cathodic diffusion layer width as dominant length scale for morphological instability and emerging dendrites.

[Phys. Rev. Fluids 9, 053701] Published Wed May 22, 2024

Author(s): Eric C. P. Breard, Luke Fullard, and Josef Dufek

This work studies the rheology of dense granular media, exploring the effects of varying particle size, density, friction and shear profiles across different flow regimes. Utilizing the discrete element method (DEM), the research extends current models by integrating volumetric contributions and introducing a new power-law scaling that unifies local and nonlocal rheology data onto a single master curve. This approach bridges the μ(I)-rheology and Kinetic Theory, offering a framework for predicting the behavior of granular flows in various settings, from geophysical flows to industrial processes.

[Phys. Rev. Fluids 9, 054303] Published Wed May 22, 2024

Author(s): Xue-Lu Xiong (熊雪露), Shujin Laima (赖马树金), Hui Li (李惠), and Yi Zhou (周毅)

We present a self-similarity analysis of single-point turbulent statistics across different quadrants in turbulent wakes. We show here that within the wake self-similar region, the distribution of the Reynolds shear stress in different quadrants can also attain a state of self-similarity. The length scaling is the same for the Reynolds shear stress and its different quadrant contributions, while there exists a difference in velocity scaling. There exists a strong connection between ejection events and large-scale coherent structures, as well as deceleration extreme events.

[Phys. Rev. Fluids 9, 054608] Published Wed May 22, 2024

Author(s): Soumen Chakravarty and V. Narayanaswamy

This article presents the first ever systematic demonstration of the drag reduction at supersonic speed regime caused by non-rigid surfaces prepared using compliant viscoelastic coating. This work lays the foundation to a new engineering paradigm that fuses engineered surfaces to create positive aerodynamic outcomes at speeds that are relevant to aerial vehicles.

[Phys. Rev. Fluids 9, 054609] Published Wed May 22, 2024

Author(s): Randall D. Kamien and Daniel Ucko

[Phys. Rev. Fluids 9, 050001] Published Tue May 21, 2024

Author(s): Xuan Zhang, Philipp Reiter, Olga Shishkina, and Robert E. Ecke

Wall modes and bulk modes compete in small-aspect-ratio rapidly rotating Rayleigh-Bénard convection. Wall modes remain robust in the presence of bulk convection and contribute substantially to the global heat transport.

[Phys. Rev. Fluids 9, 053501] Published Tue May 21, 2024

Author(s): Oscar J. Punch, Daniel J. Holland, Andreas Baumann, and Peter Eberhard

Numerical simulations of wet particles often use the particle roughness as a minimum separation criterion to limit the viscous force. Here we investigate the validity of this through a comparison of experiments of binary wet particle collisions to numerical discrete element method (DEM) and smoothed particle hydrodynamics (SPH) simulations.

[Phys. Rev. Fluids 9, 054302] Published Tue May 21, 2024