Latest papers in fluid mechanics

Author(s): Friso H. Hartog, Michiel van Nesselrooij, Olaf W. G. van Campenhout, Ferry F. J. Schrijer, Bas W. van Oudheusden, and Kunal Masania

Substrates with streamwise-preferential permeability are theorized to reduce drag in turbulent boundary layers by relaxing the no-slip condition. This study presents the first experimental validation of this concept in airflow using a 3D-printed structure. Contrary to predictions, results show an increase in drag driven by the inverse wall-normal Forchheimer coefficient, agreeing with recent direct numerical simulation data on acoustic liners. The findings highlight the challenge of modeling porous substrates for drag predictions, and suggest that translating their abstraction into physical realizations relevant for practical applications would result in structures similar to riblets.

[Phys. Rev. Fluids 9, 114602] Published Mon Nov 04, 2024

Author(s): Kuvvat Garayev and David W. Murphy

Metachronal swimming is a common form of locomotion in which organisms stroke multiple appendages sequentially. It is used by many aquatic organisms, including paramecia, copepods, ctenophores, and krill, and spans the viscous to inertial regimes across seven orders of magnitude of Reynolds numbers (Re). Through analysis of morphological and kinematics data collected from the literature, we find a strong power law relationship between Re and the Swimming Number Sw, which describes the appendage kinematics. This scaling law is maintained for all flow regimes, explains why metachronal swimming is successful at low Re, and may be useful in designing bio-inspired metachronally paddling robots.

[Phys. Rev. Fluids 9, L111101] Published Mon Nov 04, 2024

Author(s): Minyoung Kim and Ali Borhan

Mass transfer to the reactive wall of a curved cylindrical tube is analyzed in the combined entry region where both momentum and concentration boundary layers are developing. The velocity and concentration distributions developing from uniform inlet profiles are obtained using perturbation analysis,…

[Phys. Rev. E 110, 055101] Published Mon Nov 04, 2024

Author(s): Umang N. Patel, Jonathan P. Rothstein, and Yahya Modarres-Sadeghi

We perform CFD simulations to study vortex-induced vibrations of a cylinder in inertial-elastic flow and in the range of Reynolds and Weissenberg numbers where both inertia and elasticity of the flow must be considered. For increased fluid elasticity, we observe significant polymer deformation in the upstream stagnation region resulting in a region of large elastic stress that acts as a wall around the cylinder. The region of flow separation is both widened and extended further downstream. We show that higher harmonic forces which cause increased structural fatigue and are typically observed for two-degrees-of-freedom in a Newtonian flow are suppressed by adding elasticity to the flow.

[Phys. Rev. Fluids 9, 113301] Published Fri Nov 01, 2024

Author(s): K. M. Grayson, L. J. Irvine, A. G. W. Lawrie, and S. B. Dalziel

This work reveals a before unknown pathway to triadic resonance of an internal gravity wave beam. Previously, for a finite-width beam, this resonance was only known to occur after the beam was forced at a sufficient amplitude. We now show how, when turbulent structures (vortex rings and bubbles) interact with and sufficiently disturb the beam, this resonance can occur at lower amplitudes. In some cases this resonance decays and in others it is self sustaining, long after the disturbance from the turbulent structure has decayed. These findings call into question our current description of a internal wave beams pathway to triadic resonance.

[Phys. Rev. Fluids 9, 114801] Published Fri Nov 01, 2024

Author(s): F. Guglietta and F. Pelusi

The present study provides a comprehensive analytical prediction for the steady-state deformation and inclination angle of drops under shear flow, considering both confinement and interface viscosity. By merging the theories for confined and unconfined drops, the model accurately captures the behavior across a wide range of conditions, offering a robust tool for applications in complex fluids. Immersed boundary-lattice Boltzmann simulations were performed to further validate the results.

[Phys. Rev. Fluids 9, 103603] Published Wed Oct 30, 2024

Author(s): Cheng Cheng and Lin Fu

We employ second-order spectral stochastic estimation (SSSE) to investigate scaling behaviors of the couplings between physical fields, which include velocity-temperature and velocity-pressure couplings. Particular attention is given to differences between the SSSE and the first-order version (FSSE). Several metrics are proposed to compare their accuracy in estimating the thermodynamic fields with the velocity input in the logarithmic region. The SSSE has an advantage over the FSSE in estimating strong events and thermodynamic field variations. However, there is little difference in the ability of FSSE and SSSE to capture transient characteristics of near-wall thermodynamic fields.

[Phys. Rev. Fluids 9, 104607] Published Tue Oct 29, 2024

Author(s): Zhiguo Tian, Yunfan Huang, and Moran Wang

This work presents an analytical solution of flow through disordered porous media with inertia effects at a finite Reynolds number (Re), and consequently a truncated quadratic formula for easy use without any fitting parameters. The derivation is based on an effective capillary model in which the effective radius of capillaries varies with Re. Inspired by the asymptotic solution of flow in curved capillaries, the Oseen-form equation is derived to capture the flow behavior in each capillary. The analytical formula has been validated by comparisons with numerous available experimental data.

[Phys. Rev. Fluids 9, L102101] Published Mon Oct 28, 2024

Author(s): Praneet Prakash, Marco Vona, and Raymond E. Goldstein

When the 17th century Dutch microscopist Antonie van Leeuwenhoek discovered swimming “animalcules” called rotifers he observed that they often adhere to surfaces. A new analysis explains this by showing that as rotifers swim by the action of groups of cilia on either side of their mouth, the resultant fluid flows turn the rotifer to align perpendicular to a surface, pulling it in until it makes contact. This is precisely the opposite of what happens with green algae, whose breaststroke beating of its two flagella turns a cell away from the wall. Once attached, the rotifer rotates in place until random motions detach it, and it swims off in a new direction, leading to a random walk.

[Phys. Rev. Fluids 9, 103101] Published Fri Oct 25, 2024

Author(s): Defne E. Ozan and Luca Magri

Adjoint methods have been central in gradient-based optimization but traditionally require known governing equations. In this paper, we introduce a data-driven approach that utilizes echo state networks (ESNs) to infer adjoint sensitivities from data, even in cases where the system’s equations are unknown, or the data are subjected to noise. By embedding physical knowledge into the network architecture, the method accurately predicts sensitivities to parameters and initial conditions in a nonlinear thermoacoustic system. This framework opens new possibilities for gradient-based data-driven design optimization.

[Phys. Rev. Fluids 9, 103902] Published Fri Oct 25, 2024

Author(s): Daniël P. Faasen, Detlef Lohse, and Devaraj van der Meer

If carbon dioxide dissolves into a body of water, a CO2-rich boundary layer forms at the interface, which is denser in comparison to pure water, leading to the onset of buoyancy-driven convection and, consequently, the shedding of a buoyant plume. We look at the influence of confinement on this process in two ways. First, we focus on expanding our understanding of the short-time, transient diffusion of CO2 into a vertical water barrier confined to a narrow cylindrical cell. Secondly, we investigate the long-time, steady mass transfer dynamics in the liquid barrier by trapping a slug bubble underneath the liquid barrier and varying the barrier height and partial CO2 pressure.

[Phys. Rev. Fluids 9, 103501] Published Thu Oct 24, 2024

Author(s): Michael Maalouly, Guillaume Lapeyre, and Stefano Berti

New, high-resolution satellite altimetry is starting to reveal ocean turbulent flows at submesoscales, which are key to climate and marine ecology. However, the resulting velocity fields essentially represent the geostrophic flow component, while at these scales ageostrophic dynamics should start to become important. Using numerical simulations, we investigate the impact of unresolved ageostrophic motions on Lagrangian tracer dispersion. We find that filtering out ageostrophy only weakly affects dispersion, except for an overestimation of the typical pair-separation rate. Yet, it clearly misses transient particle clustering, which is found to be quite intense even at low Rossby numbers.

[Phys. Rev. Fluids 9, 104503] Published Thu Oct 24, 2024

Author(s): Kapil Dev and Chunendra K. Sahu

Geothermal temperature gradients may influence the fluid dynamics and convection developed during CO2 sequestration in deep saline aquifers. Here, we explore the intricate interplay in thermosolutal convection developed by vertical temperature and concentration gradients. By analyzing instability, we present insights into optimum conditions for enhanced convection and mixing between CO2 and brine.

[Phys. Rev. Fluids 9, 103803] Published Wed Oct 23, 2024

Author(s): Dehai Yu, Pengfei Yang, Lianjie Yue, and Zheng Chen

Detonation initiation induced by thermal nonuniformity in a supersonic reactive flow is analyzed with a theoretical model in one and two dimensions. A self-strengthening coupling between the reaction front and the induced shock wave is found to provide an underlying mechanism for detonation initiation. To quantify the capability of the thermal nonuniformity to cause detonation initiation, we introduce a detonation initiation factor. This factor is found to change nonmonotonically depending on the temperature difference of the thermal nonuniformity.

[Phys. Rev. Fluids 9, 103201] Published Tue Oct 22, 2024

Author(s): Mathieu Alonzo, Nathaniel J. Karst, Thomas Podgorski, John B. Geddes, and Gwennou Coupier

The blood microcirculatory network is where nutrients, respiratory gases, and metabolic waste products are exchanged with the neighboring cells. Here, these components can take unexpected routes to get from one point to another. Whereas a simple fluid would follow the most direct route, we show in our in vitro experiments that red blood cells, which are responsible for oxygenating the body, can intermittently take side routes and remain in the network longer than expected. These observations, backed up by associated modeling, raise new questions regarding hypoxia mechanisms in organs, even under apparently healthy conditions.

[Phys. Rev. Fluids 9, 104401] Published Tue Oct 22, 2024

Author(s): Yoni Reingewirtz, David Hasin, and René van Hout

In the manufacturing process of composite materials, jet flows are commonly used to deposit anisotropic particles such as fibers. The strength or optical properties are dictated by fiber orientation, amongst others. This study investigated the motion of fibers in co-axial jet flows. In particular, the translational and rotational motion of fibers exiting from the inner jet is linked to the strong internal shear layer (ISL) existing between the fast moving outer jet and the slow moving inner jet. We show that fibers are strongly affected by the toroidal vortices in the ISL and that their translational and rotational motion can exceed that of the local fluid flow due to the “sling effect”.

[Phys. Rev. Fluids 9, 104305] Published Mon Oct 21, 2024

Author(s): Emeric Boigné, Sadaf Sobhani, Joseph C. Ferguson, and Matthias Ihme

Chemically reacting flows through porous media are widespread in biological, environmental, and engineering applications. Yet, understanding these flows remains an outstanding challenging. This letter reveals that hydrodynamic dispersion affects reaction fronts in ways analogous to free turbulence. Our findings thus point to a regime diagram that elucidates the pore-scale coupling between fundamental processes, offering valuable theoretical insights into these complex flows.

[Phys. Rev. Fluids 9, L101201] Published Mon Oct 21, 2024

Author(s): Xi-Yuan Yin, Wesley Agoua, Tong Wu, and Wouter J. T. Bos

Many factors influence the long-time behavior and mixing of a passive scalar field transported by a two-dimensional (2D) fluid flow. Our investigations based on statistical mechanics and numerical simulations suggest that the correlation of the scalar field with the flow’s vorticity field is an important factor: strong correlation with the vorticity field is detrimental to mixing. This is linked to the inverse cascade in 2D turbulence and the persistence of large scale vortical structures.

[Phys. Rev. Fluids 9, 104502] Published Fri Oct 18, 2024

Author(s): Chungil Lee, Yuta Ozawa, Takayuki Nagata, Tim Colonius, and Taku Nonomura

The present study proposes a method to estimate time-resolved three-dimensional velocity fields for underexpanded, screeching jets based on a linear stochastic estimation with non-time-resolved velocity data and time-resolved acoustic data. The proposed method can reconstruct three-dimensional velocity fluctuation fields associated with screech at the same sampling rate (200 kHz) as the microphone measurement. The azimuthal characteristics in different screech modes are investigated. We found that the flapping structure in the B mode exhibits random clockwise and counterclockwise rotations over an extended time domain. In addition, the flapping structure is first identified in the C mode.

[Phys. Rev. Fluids 9, 104604] Published Fri Oct 18, 2024

Author(s): Hiromichi Kobayashi, Satoshi Yui, and Makoto Tsubota

Superfluid helium consists of a mixture of inviscid superfluid and viscous normal fluid. The normal fluid is affected by quantized vortices through mutual friction. Two models have been used to describe this interaction: the two-way coupled mutual friction (2W) model using experimental parameters and the self-consistent two-way coupled mutual friction (S2W) model independent of experimental parameters. This study compares the two models in detail regarding quantized vortex ring propagation, reconnection, and thermal counterflow, and provides their advantages and limitations.

[Phys. Rev. Fluids 9, 104605] Published Fri Oct 18, 2024