Latest papers in fluid mechanics

Author(s): D. Panda, L. Kahouadji, A. M. Abdal, L. S. Tuckerman, S. Shin, J. Chergui, D. Juric, and O. K. Matar

This paper is associated with a poster winner of a 2023 American Physical Society Division of Fluid Dynamics (DFD) Milton Van Dyke Award for the work presented at the DFD Gallery of Fluid Motion. The original poster is available online at the Gallery of Fluid Motion, https://doi.org/10.1103/APS.DFD.…

[Phys. Rev. Fluids 9, 110514] Published Fri Nov 22, 2024

Author(s): Ziqiang Ma, Wanqiu Zhang, and Xinping Zhou

When droplets impact solid surfaces with different contact angles, different types of jets are produced. The atomized jet is observed in the low-speed and small-contact-angle region. The atomized jet produces droplets of smaller sizes and faster velocities compared to other jet types.

[Phys. Rev. Fluids 9, 113603] Published Fri Nov 22, 2024

Author(s): Huzaif Rahim, Vasileios Angelidakis, Thorsten Pöschel, and Sudeshna Roy

Shearing shape-anisotropic grains in a split-bottom shear cell form a localized shear band with a depression at its center. Our study reveals how particle alignment affects the packing density, stress distribution, macro-friction, viscosity, and shear-thinning behavior with the increase in the aspect ratio of the particles. A scaling law correlates the particle aspect ratio to macroscopic friction and effective viscosity, revealing shear-thinning behavior in the bulk and near the surface.

[Phys. Rev. Fluids 9, 114304] Published Fri Nov 22, 2024

Author(s): Thomas G. J. Chandler and Saverio E. Spagnolie

A nematic liquid crystal, a phase of matter composed of rod-like molecules, exhibits a tendency towards uniform molecular alignment. Bodies inserted into such a fluid can disturb this orientational order, resulting in elastic stresses in the bulk fluid, which may be relaxed by body repositioning or deformation. We review classical work on rigid particles and their interactions in nematic liquid crystals, and more recent work on the shapes and interactions of deformable bodies in this complex fluid medium.

[Phys. Rev. Fluids 9, 110511] Published Wed Nov 20, 2024

Author(s): Haodong Zhang, Yifan Yang, Linye Li, Yang Lin, Fei Qi, and Xi Xia

Pinch-off of premixed flames typically results from flame extinction induced by aerodynamic strain. However, for a jet diffusion flame, we find the strain effect to be secondary. Instead, pinch-off is initiated by an insufficient fuel supply to the reaction region, as a result of outward fuel diffusion overwhelmed by inward convection. This competition of transport effects inspires the definition of a characteristic Peclet number as the pinch-off criterion.

[Phys. Rev. Fluids 9, 113202] Published Wed Nov 20, 2024

Author(s): Kerry S. Klemmer and Michael F. Howland

As wind turbines increase in scale and are deployed in diverse atmospheric conditions, understanding wake dynamics in stratified atmospheric boundary layers becomes critical. This study uses large eddy simulations to analyze the mechanisms that govern wake momentum deficit and added turbulence kinetic energy transport in stable and neutral atmospheric boundary layers. Findings reveal that dynamics are strongly influenced by effects of stratification on the atmospheric inflow, rather than buoyant forcing, and the dependence of wake-added turbulence on stability. These insights can guide new models that better predict wakes across conditions, contributing to more efficient wind power.

[Phys. Rev. Fluids 9, 114607] Published Wed Nov 20, 2024

Author(s): Georgy Zinchenko, Vladyslav Pushenko, and Jörg Schumacher

Anomalous dissipation in turbulence is a dissipation mechanism of kinetic energy that is independent of fluid viscosity; this mechanism requires sufficiently rough velocity fields at high Reynolds numbers. Our study links this statistical behavior to fundamental vortex stretching mechanisms, exploring both, classical kinematic Burgers vortex models and simulations of three-dimensional box turbulence. We identify intense vortex structures in turbulence as key contributors to anomalous dissipation, offering insights into the underlying dynamics of energy transfer in turbulent flows.

[Phys. Rev. Fluids 9, 114608] Published Wed Nov 20, 2024

Author(s): Peng-Jun-Yi Zhang, Nan-Sheng Liu, Zhen-Hua Wan, De-Jun Sun, Xi-Yun Lu, Jian-Qiang Chen, and Si-Wei Dong

We conduct comprehensive investigations by direct numerical simulations on the wall heat flux (WHF) in the hypersonic boundary layer over the windward side of a lifting body, which is affected by non-canonical effects, such as the wall curvature and pressure gradient. Based on the framework of conditional analysis, the generation mechanism of extreme WHF events is illustrated in two perspectives: identifying the coherent structures and quantitatively characterizing energy transport. We explore quite different features of WHF in the central and side regions of the lifting body.

[Phys. Rev. Fluids 9, 114609] Published Wed Nov 20, 2024

Author(s): Florian Kogelbauer and Ilya Karlin

Exact closure for hydrodynamic variables is rigorously derived from the linear Boltzmann kinetic equation. Our approach, based on spectral theory, structural properties of eigenvectors, and the theory of slow manifolds, allows us to define a unique, optimal reduction in phase space close to equilibr…

[Phys. Rev. E 110, 055105] Published Wed Nov 20, 2024

Author(s): Beichen Tian, Zijian Zong, Yue Wu, Biao Huang, and Dengcheng Liu

This study explores the evolution characteristics of pressure pulses caused by cavitating flow around a highly-skewed propeller. The fluctuation law of low-frequency pressure around the propeller is mainly determined by the rotational motion of the propeller, which is less affected by cavitation. The occurrence, rupture, shedding, and collapse of a vapor cavity will promote a significant increase in medium and high frequency pressure. Most notably, the fragmentation and shedding of small-scale cavities can cause pressure peaks in the mid-frequency region. Meanwhile, the collapse of microbubbles will lead to pressure pulses fluctuating at a decreased rate of 6 dB per octave.

[Phys. Rev. Fluids 9, 114302] Published Tue Nov 19, 2024

Author(s): D. D. Carvalho, Y. Bertho, A. Seguin, E. M. Franklin, and B. Darbois Texier

When multiple intruders move through a granular material, complex grain-mediated interactions can arise between them. In this study, we experimentally investigate the case of two spheres moving side by side in a granular medium, focusing on how their interaction affects the drag force experienced by each sphere. Our results show that the presence of a neighboring sphere reduces the drag on the first sphere, with this reduction becoming more significant as the spheres are closer to each other. Furthermore, the amount of relative drag reduction is observed to increase with the intruders’ depth in the granular medium.

[Phys. Rev. Fluids 9, 114303] Published Tue Nov 19, 2024

Author(s): Marc Plasseraud and Krishnan Mahesh

Secondary streamlines (left half) and stagnation pressure isolines (right half) colored by stagnation pressure, in a transverse view of the 6:1 prolate spheroid for a Reynolds number based on length of 10,000 and an angle of attack of 70 degrees. A high degree of correlation is observed between the streamlines and the stagnation pressure isolines, which are able to capture the complexity of the vortical flow. Thus, the current study proposes to use the largest closed isolines of stagnation pressure as a boundary for a vortex.

[Phys. Rev. Fluids 9, 114701] Published Tue Nov 19, 2024

Author(s): Johann Herault, Laura Paez, Kamilo Melo, Robin Thandiackal, Vincent Lebastard, Frédéric Boyer, and Auke Ijspeert

The goal of this article is to identify and understand the fundamental role of spatial symmetries in the emergence of undulatory swimming using an anguilliform robot. Here, the local torque at the joints of the robot is controlled by a chain of oscillators forming a central pattern generator (CPG). …

[Phys. Rev. E 110, 055104] Published Mon Nov 18, 2024

Author(s): Yukai Lin, Canjun Zhao, Fuqiang Chu, Xiaomin Wu, and Nenad Miljkovic

Since 1756, Leidenfrost droplets have been extensively investigated for their intriguing physics and promising applications. Here, we identify and study an interesting phenomenon which we term Leidenfrost droplet billiard ball collision, providing an answer to the fate of two identical Leidenfrost droplets after they collide. Fundamental mechanisms governing the collision between multiple Leidenfrost droplets are elucidated, expanding the temperature range of droplet manipulation technologies from room temperature to several hundred degrees Celsius. This work helps guide the development of liquid transport technologies for a plethora of applications, such as selective chemical synthesis.

[Phys. Rev. Fluids 9, L111601] Published Mon Nov 18, 2024

Author(s): Umair Ahmed, Nilanjan Chakraborty, and Markus Klein

Flame-wall interaction (FWI) for two flame configurations under different laminar burning velocity to nonreacting wall friction velocity ratios is investigated. The flame orientations with respect to the streamwise component of velocity and wall-normal direction have a significant impact on the variations of wall heat flux, wall shear stress, and wall friction velocity in premixed FWI within turbulent boundary layers. The behavior of nondimensional streamwise velocity and nondimensional temperature using wall units for different laminar burning velocity to nonreacting wall friction velocity ratios show that the standard log-law profiles in wall units are not valid.

[Phys. Rev. Fluids 9, 113201] Published Mon Nov 18, 2024

Author(s): Yun Chang and Alberto Scotti

Radiatively driven convection in freshwater lakes occurs when water temperature is below that of maximum density (3.98 ℃); as solar radiation penetrates a lake, the surface becomes warmer, denser, and sinks. We derived the vertical velocity scale and buoyancy flux profile, which are then verified by large eddy simulations. Convection cells in inertial frames grow continuously, whereas the Coriolis effect confines the growth. The duration of radiative forcing is a second factor arresting the growth.

[Phys. Rev. Fluids 9, 113503] Published Mon Nov 18, 2024

Author(s): Muhammad Abdullah and George I. Park

Fluid suction/injection through porous boundaries is a classic strategy for boundary-layer control. However, its utility in channel flows is comparatively ambiguous. Using two canonical configurations, we show that non-modal perturbations well below the linear instability threshold are heavily amplified by weak vertical crossflows. Only very strong (thus costly) crossflows can sufficiently inhibit modal and non-modal instabilities. However, these are shown to be accompanied by declining mass flow rates, deprecating any apparent advantage. Our results challenge previous literature and the suitability of crossflow-based control in internal flows.

[Phys. Rev. Fluids 9, 113901] Published Mon Nov 18, 2024

Author(s): Rory T. Cerbus and Tom Mullin

The Moody diagram is a well-known engineering plot of friction factor versus flow rate which shows definite relationships over the majority of parameter space. However, in the transitional regime between laminar and turbulent flows where the relationships are deemed indefinite the region is shown hatched. We investigate the transitional regime using a novel method to minimize the influence of initial conditions. This regime is approached from above by reducing the flow speed from a turbulent flow state. We find that flows driven by a constant pressure difference yield a single curve near the maximum of Moody’s hatches, while flows driven by a syringe produce a distinctly different curve.

[Phys. Rev. Fluids 9, 113902] Published Mon Nov 18, 2024

Author(s): Zhaodong Ding, Chengxi Zhao, Kai Mu, and Ting Si

Liquid jets under interfacial shear effects are critical in various scientific and industrial applications. External shear induces axial elastic tension due to velocity gradients across the jet, significantly impacting the linear instability of viscoelastic jets. This study, using slender-jet approximations, reveals that standard models fail to account for the effects of elastic tension. Higher-order approximation models, including parabolic and averaged-parabolic models, are developed to capture these effects accurately, offering a new stabilization mechanism for viscoelastic jets and providing insights for future research.

[Phys. Rev. Fluids 9, 114001] Published Mon Nov 18, 2024

Author(s): Emeka Peter Mazi, Hamad El Kahza, and Pejman Sanaei

In this work, we study the deposition and erosion of solid particles at the microscale level and their direct consequences on the internal structure of porous media with branching structure consisting of axisymmetric channels, undergoing a unidirectional flow. We characterize the evolution of the internal morphology of the porous medium using geometric parameters such as the gradients of initial pore radii and layer thicknesses.

[Phys. Rev. Fluids 9, 114301] Published Mon Nov 18, 2024