Physical Review Fluids

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

Author(s): Xiaofeng Wei, Dege Li, Jing Lei, Jinglu Li, Javier Rivero-Rodríguez, Fangye Lin, Dongyun Wang, and Benoit Scheid

In this paper, we investigate the exit dynamics of a sphere launched underneath a liquid bath surface at a prescribed impact velocity. Spheres with radii approximate or smaller than the capillary length are considered. The process can be sequenced into a partial exit stage that forms a coated layer, and a full exit stage with an attached ligament. A bouncing-off regime, a lower pinch-off penetration regime, and an upper pinch-off penetration regime are identified, separating by a penetration Weber number and a switching Weber number. The phase diagram is revealed, where the two critical Weber numbers are functions of the Bond number.

[Phys. Rev. Fluids 9, 054003] Published Fri May 17, 2024

Author(s): Qiang Du, Yaguang Xie, Lei Xie, and Ruonan Wang

We integrated theoretical analysis and numerical simulations to investigate the turbulence transition through a crossflow instability in the boundary layer of a cooler rotating disk within a rotor-stator cavity, influenced by a temperature gradient. This gradient induces centrifugal buoyancy forces that alter the radial inflection points in the mean flow. These changes lead to premature bifurcation of spiral waves, crucial in the transition process, resulting in an early onset of turbulence in the boundary layer of the rotating disk. Our findings underscore the importance of manipulating boundary layer stability via temperature gradients to control turbulent transitions.

[Phys. Rev. Fluids 9, 053908] Published Wed May 15, 2024

Author(s): L. H. O. Hellström, T. Van Buren, J. C. Vaccaro, and A. J. Smits

To investigate the existence of geometrically self-similar eddies in fully developed turbulent pipe flow, stereoscopic particle image velocimetry measurements were performed in two parallel cross-sectional planes, for friction Reynolds numbers Reτ = 1310, 2430, and 3810. The instantaneous turbulence structures are sorted by width using an azimuthal Fourier decomposition, then azimuthally aligned to create a set of average eddy velocity profiles. The streamwise similarity is investigated using two-point correlations. Over the range of scales examined, the candidate structures establish full three-dimensional geometric self-similarity.

[Phys. Rev. Fluids 9, 054607] Published Wed May 15, 2024

Author(s): J. J. Taylor-West and A. J. Hogg

Scraping of a thin layer of viscoplastic fluid from a horizontal surface by a translating rigid scraper generates a mound of fluid upstream of the scraper and a residual layer behind it. We compute numerical solutions for the system modeled via viscoplastic shallow-layer theory. The unsteady dynamics of this system exhibit a variety of self-similar regimes, for which we construct solutions explicitly and identify key scalings for the temporal development of the mound. We further report experimental results, which are compared with predictions from the shallow-layer theory, obtaining reasonable agreement once a slip boundary condition is included in the model.

[Phys. Rev. Fluids 9, 053301] Published Tue May 14, 2024

Author(s): Jonathan B. Freund

The dynamics of a free object in an active nematic suspension in a circular container are simulated. For ranges of parameters, unstable chaotic wanderings eventually reach either a fixed-point or limit-cycle (shown) behavior. These flows are analyzed, and similar behaviors confirmed to also occur in more complex geometries.

[Phys. Rev. Fluids 9, 053302] Published Tue May 14, 2024

Author(s): Yijiang Yu and Michael D. Graham

We present a numerical study of a thin elastic sheet with small extensibility sedimenting in a viscous fluid in free space or near a wall. The interplay between gravity and the elastic response of sheets gives rise to complex deformation and reorientation dynamics. Near a vertical wall, sheets exhibit asymmetric conformations that cause the sheet to drift toward or away from the wall. Near an inclined wall, sheets show qualitatively different dynamics when the wall angle is large: they either deposit on or slide along the wall with a fixed wall-normal distance.

[Phys. Rev. Fluids 9, 054104] Published Tue May 14, 2024

Author(s): Varun Kulkarni, Suhas Tamvada, Nikhil Shirdade, Navid Saneie, Venkata Yashasvi Lolla, Vijayprithiv Batheyrameshbapu, and Sushant Anand

Drops impacting supercooled surfaces adhere to them due to contact line pinning and their solidification. However, distinguishing the influence of each phenomenon on post-impact behavior is challenging since even repellent materials exhibit some drop adhesion. In this study, we examine the impact of water and alkane drops on an omniphobic dry ice surface. We show that the solidification extent within the drop, combined with thermal, elastic, and surface tension forces, dictate outcomes like fragmentation, rebound, or no-bounce. Our findings have critical implications for material design in 3D printing, frost-resistant coatings, and safe biological material transport in cold climates.

[Phys. Rev. Fluids 9, 053604] Published Mon May 13, 2024

Author(s): Sofia Saoncella, Si Suo, Johan Sundin, Agastya Parikh, Marcus Hultmark, Wouter Metsola van der Wijngaart, Fredrik Lundell, and Shervin Bagheri

Liquid infused surfaces (LISs) are a nature-inspired surface technology that demonstrates multiple functionalities under laminar and controlled flow conditions. We study experimentally the behavior of the infused lubricant under submerged conditions and turbulent flow. When exposed to turbulence, the lubricant layer develops into a pattern of droplets, the length of which depends on the balance between shear and contact force. The stability of the droplets prevents complete drainage of the lubricant and increases the robustness of the LIS in the presence of turbulence. We identify a model that predicts the equilibrium length of the droplets and validate it with numerical simulations.

[Phys. Rev. Fluids 9, 054002] Published Mon May 13, 2024

Author(s): Daniel G. Boettger, Shane R. Keating, Michael L. Banner, Russel P. Morison, and Xavier Barthélémy

We examine the influence of wind forcing on the inception of breaking in surface gravity waves using an ensemble of high-resolution numerical simulations. We find that there is a critical point in the energetic evolution of the wave in which the convergence of kinetic energy at the wave crest can no longer be offset by conversion to potential energy, resulting in a rapid growth of kinetic energy up to breaking onset. This energetic signature is shown to consistently differentiate between non-breaking and breaking waves under a range of wind forcing speeds.

[Phys. Rev. Fluids 9, 054803] Published Mon May 13, 2024

Author(s): Mohammed Bendaoud, Mehdi Abbasi, Alexis Darras, Hamid Ez-Zahraouy, Christian Wagner, and Chaouqi Misbah

Exploring how the shape of red blood cells influences their flow properties, this study uses numerical simulations to analyze changes from healthy bi-concave forms to abnormal spherical shapes associated with disorders like spherocytosis. The research reveals complex, non-monotonic relationships between cell shape and flow rate across varying channel widths, and its impact on blood perfusion.

[Phys. Rev. Fluids 9, 053603] Published Fri May 10, 2024

Author(s): Byeonguk Ahn, Håkon T. Nygård, Nicholas A. Worth, Zhijian Yang, and Larry K. B. Li

To explore the dynamics of annular combustors, we investigate azimuthal thermoacoustic instabilities under a range of hydrogen power fractions and operating conditions. Using time-series analysis and mode detection techniques, we examine the relationship between longitudinal and azimuthal modes, identifying a transition from chaos to high-amplitude periodic states. Our research sheds light on how hydrogen enrichment affects combustor stability and presents the first identification of type-II Pomeau–Manneville intermittency in annular combustors. These findings contribute to knowledge of the modal dynamics within combustors, with implications for the design and operation of future systems.

[Phys. Rev. Fluids 9, 053907] Published Fri May 10, 2024