Physical Review Fluids
Response of turbulent energy spectrum and flow structures when vortical motion of a certain scale is suppressed by artificial forcing
Author(s): Masato Hirota, Seiichiro Izawa, and Yu Fukunishi
The energy cascade in turbulence is explored through a novel approach in which the vortical structures of a certain scale in the inertial subrange, colored by yellow, is forcibly suppressed. Their disappearance leads to a slight increase in kinetic energy in the larger scale range and a decrease in the smaller scale range. The vortex-tracking analysis reveals that the vortices twice as large as the target, colored by blue, exhibit smaller curvatures and longer lifespans, while no remarkable changes are found for the vortices that are four times larger, colored by red. These findings indicate that the larger vortices are locally bent by the smaller vortices, shortening their lifespans.
[Phys. Rev. Fluids 9, 084602] Published Wed Aug 07, 2024
Curvature-driven transport of thin Bingham fluid layers in airway bifurcations
Author(s): Cyril Karamaoun, Haribalan Kumar, Médéric Argentina, Didier Clamond, and Benjamin Mauroy
We uncover and study a physical process that is hidden in the healthy lung. This process can be triggered by the thickening of the thin layer of mucus lining the bronchi walls. At the air-mucus interface, surface tension and curvature can combine to oppose the physiological motion of mucus induced by cilia, causing mucus to stall or, even, move in reverse. Representing mucus as a Bingham fluid, we characterize analytically the fluid dynamics in the thin layer using dimensionless quantities and employ numerical simulations to compute the layer velocity field in airways bifurcations. This work sheds new light on the intricate workings of the respiratory system.
[Phys. Rev. Fluids 9, L081101] Published Wed Aug 07, 2024
Gravito-capillary trapping of pendant droplets under wet uneven surfaces
Author(s): Etienne Jambon-Puillet
Pendant drops spontaneously appear on the underside of wet surfaces through the Rayleigh-Taylor instability. Here, I show that such pendant drops can get stuck on topographic defects, despite having no contact line. Unlike traditional pinning, the trapping force has a gravito-capillary origin: liquid has to move up or down and the interface has to deform for the drop the pass the defect. I model this topography induced force, demonstrate how to harness it to guide pendant drops, and expect it to be relevant to other contact line free systems.
[Phys. Rev. Fluids 9, L081601] Published Wed Aug 07, 2024
Biophysical fluid dynamics in a Petri dish
Author(s): George T. Fortune, Eric Lauga, and Raymond E. Goldstein
In biological fluid dynamics, as studied in the lab or in natural environments, it is often the case that organisms swim in a thin fluid layer above a bottom no-slip surface and below an upper stress-free interface. Here we examine in this “Petri dish” geometry the image system for the elementary and composite singularities of Stokes flow: the Stokeslet, rotlet, source, rotlet dipole, source dipole and stresslet. As an application of these results, we reconsider the problem of hydrodynamic bound states of spherical microswimmers in finite-depth chambers.
[Phys. Rev. Fluids 9, 083101] Published Mon Aug 05, 2024
Improved two-temperature model with correction of non-Boltzmann effect for oxygen and nitrogen
Author(s): Rui Xiong, Yufeng Han, and Wei Cao
The substantial rise in fluid temperature behind the shock at the head of hypersonic vehicles induces molecular internal energy excitation and dissociation, potentially resulting in thermochemical nonequilibrium flow. The high vibrational energy molecule of oxygen and nitrogen undergo overdistribution and underdistribution states, resulting in increased and decreased dissociation rates in nonequilibrium flow. The latter state dominates and notably increases fluid temperature and wall heat flux, impacting the vehicle’s thermal protection design. This study proposes an improved two-temperature dissociation rate model to more accurately simulate the nonequilibrium flow behind the shock.
[Phys. Rev. Fluids 9, 083201] Published Mon Aug 05, 2024
Approximate derivation of the power law for the mean streamwise velocity in a turbulent boundary layer under zero-pressure gradient
Author(s): J. Dey
Using a Reyolds shear stress model in the boundary layer equations for flow over a flat plate, the streamwise velocity (U) is related to the wall-normal velocity (V). The empirical power-law U∼η1/n for the streamwise velocity is derived theoretically, followed by a power-law for V.
[Phys. Rev. Fluids 9, 084601] Published Mon Aug 05, 2024
Sensitivity study of resolution and convergence requirements for the extended overlap region in wall-bounded turbulence
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
Localized jammed clusters persist in shear-thickening suspension subjected to swirling excitation
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
Transient growth in diabatic boundary layers with fluids at supercritical pressure
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
Retention or repulsion forces induced by bubbles trapped at the base of an immersed microparticle on a substrate
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
From mixing to displacement of miscible phases in porous media: The role of heterogeneity and inlet pressures
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
Attached and separated rotating flow over a finite height ridge
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
Deformation of drops at low Reynolds number impact
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
Equatorial blowup and polar caps in drop electrohydrodynamics
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
Static Bell test in pilot-wave hydrodynamics
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
Thermocapillary instability of a surfactant-laden shear-imposed film flow
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
Correlations between thermodynamic fluctuations in shock wave/turbulent boundary layer interaction
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
Newtonian fluid dynamics in a misaligned parallel-plate rheometer
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
Modal and nonmodal stability of the laminar flow in a channel with longitudinal riblets
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
Dissociation of red blood cell aggregates in extensional flow
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