Latest papers in fluid mechanics

Author(s): Sergio Hoyas, Ricardo Vinuesa, Peter Schmid, and Hassan Nagib

Direct Numerical Simulations (DNS) are among the most powerful tools for studying turbulent flows. Even though the achievable Reynolds numbers are lower than those obtained through experimental means, DNS offers a clear advantage: the entire velocity field is known, allowing for evaluating any desired quantity. One is the indicator function, which is crucial for understanding inner and outer interactions in wall-bounded flows and describing the overlap region between them. We find a clear dependence of this indicator function on the mesh distributions we examined, raising questions about classical mesh and convergence requirements for DNS and achievable accuracy.

[Phys. Rev. Fluids 9, L082601] Published Mon Aug 05, 2024

Author(s): Li-Xin Shi (石理新) and Song-Chuan Zhao (赵松川)

This study reports a novel dynamic in shear-thickening suspensions with a free surface under bottom shear, revealing localized, persistent jammed clusters (bumps in the image). We clarify the essential role of shear-thickening properties and the effect of suspension depth, showing that at small depth this heterogeneous state could occur below the minimum density of discontinuous shear-thickening. Moreover, our findings emphasize the critical role of free surfaces in cluster growth. This advances our understanding of the evolution of heterogeneity associated with shear-thickened states.

[Phys. Rev. Fluids 9, 083301] Published Fri Aug 02, 2024

Author(s): Pietro Carlo Boldini, Benjamin Bugeat, Jurriaan W. R. Peeters, Markus Kloker, and Rene Pecnik

Is transient growth critical for boundary-layer stability in fluids at supercritical pressure with their strong property variations across the pseudo-boiling line? This study on non-modal growth and its competition with modal growth under various heat-transfer scenarios reveals new insights into instability mechanisms in non-ideal fluids. We identify optimal growth in streamwise-modulated streaks as the fluid is heated beyond the pseudo-boiling line, with transcritical Mode II responsible. In this scenario, transition below the critical Reynolds number might prevail, mimicking the effect of an adverse pressure gradient in the ideal-gas regime.

[Phys. Rev. Fluids 9, 083901] Published Fri Aug 02, 2024

Author(s): Anna Ipatova, Alexis Duchesne, H. N. Yoshikawa, Pascal Mariot, Corenthin Leroy, Christine Faille, Ichiro Ueno, Georg F. Dietze, and Farzam Zoueshtiagh

Our study investigates the entrapment of air bubbles beneath micrometer-sized particles upon immersion, employing theoretical, computational, and experimental approaches. We reveal that the wettability of both particles and substrates significantly influences the adhesion forces due to trapped bubbles. Our findings, validated through experiments, highlight that hydrophobic surfaces increase the likelihood of bubble entrapment, thereby enhancing particle detachment forces. This work offers valuable insights for various industries, such as food processing, where optimizing surface coatings could improve cleaning efficiency and promote greener practices.

[Phys. Rev. Fluids 9, 084301] Published Fri Aug 02, 2024

Author(s): Yahel Eliyahu-Yakir, Ludmila Abezgauz, and Yaniv Edery

Miscible multiphase flow in porous media is a key phenomenon in various industrial and natural processes, such as hydrogen storage and geological carbon sequestration. We experimentally find that inlet pressures and heterogeneity levels control the miscible displacement of high-viscosity glycerol by low-viscosity water and their mixing due to shear forces, by transitioning from uniform to fingering patterns at the pore scale. We derive a non-dimensional modified Sherwood number that links these microscale patterns to physical properties like velocity distribution, diffusion, and viscosity contrasts; thus linking pore-scale dynamics with macroscale Darcy-scale observations.

[Phys. Rev. Fluids 9, 084501] Published Fri Aug 02, 2024

Author(s): S. Frei, E. Burman, and E. Johnson

We investigate the effect of rotation on the two-dimensional boundary layer on a ridge in high Reynolds number flow using numerical simulations to consider both shallow and deep flows as well as flow past a horizontal cylinder, motivated by experimental results by Machicoane et al. In all cases the boundary layer remains attached, even at large Reynolds numbers (Re), provided the Rossby number (Ro) is sufficiently small. At larger Ro, the flow detaches at sufficiently high Re to form a steady recirculating region in the lee of the ridge; at even higher Re no steady flow is found. The figure shows streamlines at Re=256000 for Ro=1.2, 1.5 and 2.

[Phys. Rev. Fluids 9, 084801] Published Fri Aug 02, 2024

Author(s): J. S. Hansen

In this Letter, the single-element Maxwell model is generalized with respect to the wave vector and extended with a correction function that measures the reduced viscous response. This model has only two free parameters and avoids the attenuation-frequency locking present in the original model. Thro…

[Phys. Rev. E 110, L023101] Published Thu Aug 01, 2024

Author(s): L. Jørgensen

Through experiments and scaling analysis, we describe the deformation of an impacting drop at low impact Reynolds number. We focus on deformations driven by impact inertia and limited by viscous dissipation only. The main result is a universal power-law dependence of the nondimensional contact diameter in the maximum deformation state as a function of the Reynolds number, when the latter is smaller than 1. This specific case was not described before in the literature, despite its relevance in earth sciences for example.

[Phys. Rev. Fluids 9, 083601] Published Thu Aug 01, 2024

Author(s): Gunnar G. Peng, Rodolfo Brandão, Ehud Yariv, and Ory Schnitzer

We illuminate effects of surface-charge convection intrinsic to leaky-dielectric electrohydrodynamics by analyzing the symmetric steady state of a circular drop in an external field at arbitrary electric Reynolds number ReE. In particular, we characterise the development of an equatorial charge-density blowup singularity at moderate ReE (in the case where charge relaxation is slower in the drop phase than in the suspending phase) and the formation of polar stagnant caps at large ReE (in the opposite case)

[Phys. Rev. Fluids 9, 083701] Published Thu Aug 01, 2024

Author(s): Konstantinos Papatryfonos, Louis Vervoort, André Nachbin, Matthieu Labousse, and John W. M. Bush

The experimental violation of Bell’s Theorem in quantum systems is generally taken as proof of the impossibility of local hidden variable theories, as would provide a rational dynamical underpinning for quantum mechanics. We here present a platform for executing Bell tests in pilot-wave hydrodynamics, a system known to capture many features of the quantum realm. We execute a static test in a bipartite tunneling system, and rationalize the emergent violations in terms of the wave-mediated coupling between the two subsystems.

[Phys. Rev. Fluids 9, 084001] Published Thu Aug 01, 2024

Author(s): Arnab Choudhury and Arghya Samanta

We examine the linear thermocapillary instability of a two-dimensional surfactant-laden gravity-driven shear-imposed film flowing over a uniformly heated inclined wall. We observe that the surfactant Marangoni number stabilizes, while the thermal Marangoni number destabilizes H-mode, S-mode, P-mode, and shear mode. These opposing impacts establish an analytical relationship between surfactant and thermal Marangoni numbers, for which the critical Reynolds numbers for the H-mode instability of the non-isothermal and isothermal film flows coincide. When comparing results with and without inertia, we predict that inertia stabilizes surfactant mode.

[Phys. Rev. Fluids 9, 084002] Published Thu Aug 01, 2024

Author(s): Anna L. Herring, Ruotong Huang (黄若橦), and Adrian Sheppard

Diffusive transport has implications for the long-term status of underground storage of hydrogen (H2) fuel and carbon dioxide (CO2), technologies which are being pursued to mitigate climate change and advance the energy transition. Once injected underground, CO2 and H2 will exist in multiphase fluid…

[Phys. Rev. E 110, 015106] Published Wed Jul 31, 2024

Author(s): Ximeng Hou, Dehao Xu, Jianchun Wang, and Shiyi Chen

The 2nd moment correlations between thermodynamic fluctuations in shock wave/turbulent boundary layer interaction flows are numerically studied. By introducing Kovasznay modal decomposition, it is shown that the correlations are functions of inter-modal competition and inter-modal correlation. A simplified model is proposed to eliminate the impact of inter-modal correlation, and thus the correlations can be determined merely by the root-mean-square values of thermodynamic fluctuations.

[Phys. Rev. Fluids 9, 073401] Published Wed Jul 31, 2024

Author(s): Jian Teng, Sungwon La, and Jesse T. Ault

This study examines the effect that misalignment has on the viscosity measurements of Newtonian fluids in a parallel-plate rotational rheometer. Our theoretical results show that at small gap heights, misalignment can produce additional secondary velocity components and pressures in the fluid, which affect the forces and moments in the rheometer. These forces and moments on the top plate were found to increase as the misalignment tilt angle increased.

[Phys. Rev. Fluids 9, 074103] Published Wed Jul 31, 2024

Author(s): Antoine Jouin, Jean-Christophe Robinet, and Stefania Cherubini

The influence of a surface covered with riblets on laminar-turbulent transition in channel flow is investigated through modal and non-modal stability analysis of n-periodic systems, allowing to take into account detuned long-wavelength instabilities. For large riblet spacing, a wavenumber lock-in regime is observed, in which the wavelength of the optimal streaks is controlled by the riblet spacing, and the streaks amplitude is modulated in the spanwise direction via a beating mechanism, as in geometric frustration. Moreover, in the presence of harmonic forcing, riblets lead to the development of oblique waves that may trigger an early transition.

[Phys. Rev. Fluids 9, 073903] Published Mon Jul 29, 2024

Author(s): Midhun Puthumana Melepattu, Guillaume Maîtrejean, and Thomas Podgorski

Blood rheology and microcirculation are strongly influenced by red blood cell aggregation. We investigate the dissociation rates of red cell aggregates in extensional flow using hyperbolic microfluidic constrictions and image analysis by a convolutional neural network (CNN). Our findings reveal that…

[Phys. Rev. Fluids 9, L071101] Published Mon Jul 29, 2024

Author(s): M. Crialesi-Esposito, G. Boffetta, L. Brandt, S. Chibbaro, and S. Musacchio

Droplet formation is an important research topic with applications in geophysics, where fragmentation is key in the exchange between atmosphere and ocean, and in industrial processes, with many products obtained by emulsification. Despite its importance this fundamental physical problem remains a puzzle. In this work we examine small droplet formation in turbulent multiphase flows. By surgically acting on the Navier-Stokes equations we show that small-droplet formation is the main cause of high dissipation events characterizing multiphase turbulence, and not vice versa. We also prove that tiny droplets are formed through the internal capillary dynamics of large droplets during break-up.

[Phys. Rev. Fluids 9, L072301] Published Mon Jul 29, 2024

Author(s): Grant Rydquist and Mahdi Esmaily

Algorithms used to calculate red blood cell damage are often constructed empirically from laminar flows, and the extensibility of these algorithms to turbulent flows is an open question. To examine this question, we investigate the effect of turbulent flows on red blood cell damage by simulating individual red blood cells in turbulent channel flow using a multiscale computational framework. The results from the turbulence simulations are compared to laminar channel flow at equivalent wall shear stress. While the laminar flows generate greater stretch in a time-averaged sense, the turbulent flows produce spikes in deformation associated with short bursts of high-shear conditions.

[Phys. Rev. Fluids 9, 073102] Published Fri Jul 26, 2024

Author(s): Shubhra Sahu, Bapan Mondal, and Somnath Bhattacharyya

In this study we have extended the mean-field based model to analyze the layered structure of the electric double layer and found that oscillations in charge density arise in multivalent counterions. Formation of the counterion condensed layer and overscreening creates a larger accumulation of coions in the electric double layer, leading to an electroosmotic flow reversal and attenuation in ion selectivity of the pore. The present model shows that the counterion size has an impact on the condensed layer and hence, overscreening. We demonstrate that the electroosmotic flow reversal of multivalent electrolytes can be suppressed by mixing with monovalent slats.

[Phys. Rev. Fluids 9, 074201] Published Fri Jul 26, 2024

Author(s): I. Misra and V. Kumaran

The dynamics of a magnetic particle of moment m in an oscillating magnetic field H has a qualitative dependence on the magnetization model. There are sustained oscillations for a particle with a permanent dipole. The particle is static for an induced dipole with no hysteresis. For an induced dipole with hysteresis, there is a transition between oscillations with a magnetic moment oscillating about a particle axis, and a magnetic moment flipping relative to the particle axis.

[Phys. Rev. Fluids 9, 074303] Published Fri Jul 26, 2024