NEW ARTICLE
The transportation of oil through pipelines and channels is a highly energy-intensive operation, primarily due to the significant viscosity of the oil and the consequent high friction. Among the various friction reduction methods utilized in this domain, the water-lubricated approach has emerged as particularly promising. Our investigation focuses on assessing the efficacy of this technique through direct numerical simulations of turbulent channel flow. In this setup, we introduce two thin water layers near the walls, which serve to lubricate the flow of oil within the core.
Alessio Roccon, Francesco Zonta, and Alfredo Soldati
Phys. Rev. Fluids 9, 054611 (2024)
EDITORS' SUGGESTION
Often considered a childhood pastime, soap bubbles emerged as a captivating domain for rigorous scientific inquiry for generations. While blowing soap bubbles is familiar to everyone, the underlying physics of inflating them remains unanswered. In our investigation, we visualize the previously unexplored internal airflow experimentally, revealing a toroidal vortical flow that resembles a bound vortex ring. The air enters the bubble as a round jet, emerging from the nozzle opening and impinges on the expanding concave interior to form this toroidal vortex. We also predict several scaling laws for the inflation rate and dynamics of this confined vortical flow by varying the source pressure.
Saini Jatin Rao, Siddhant Jain, and Saptarshi Basu
Phys. Rev. Fluids 9, L051602 (2024)
LETTER
In this Letter, we explore the influence of colloids at liquid-liquid interfaces on droplet pinch-off dynamics in microfluidic devices. We uncover a significant deviation in droplet formation time compared to pure systems, similarly to surfactant-laden systems. Yet notably, colloids exert minimal impact on droplet size, indicating potential nonlinear effects. The dynamics of neck thinning without colloids agree with the classic pendant drop scaling laws, while particle presence replaces traditional viscous and inertial-viscous regimes with a single power law, suggesting an elastic behavior driven by soft particle interactions.
Loïc Chagot, Simona Migliozzi, and Panagiota Angeli
Phys. Rev. Fluids 9, L052201 (2024)
NEW ARTICLE
We investigate high-Reynolds-number polydisperse gravity currents propagating along a channel of general cross-section into a linearly stratified ambient fluid. We formulate and solve numerically the shallow water equations and present typical height and velocity profiles of the current and particle mass concentration. Two dimensionless parameters, Stratification (S) and particle buoyancy (Π), are relevant. Increasing S decreases the current velocity propagation, but as Π increases, the current propagates faster. For a specific S, Π dependence, an equilibrium occurs for a significant time and the system behaves like a system without particles propagating into the ambient of constant density.
T. Zemach
Phys. Rev. Fluids 9, 054105 (2024)
NEW ARTICLE
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.
Cheng Cheng and Lin Fu
Phys. Rev. Fluids 9, 054610 (2024)
NEW ARTICLE
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.
Sergiu Busuioc
Phys. Rev. Fluids 9, 053401 (2024)
NEW ARTICLE
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.
Eric C. P. Breard, Luke Fullard, and Josef Dufek
Phys. Rev. Fluids 9, 054303 (2024)
NEW ARTICLE
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.
Soumen Chakravarty and V. Narayanaswamy
Phys. Rev. Fluids 9, 054609 (2024)
NEW ARTICLE
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.
Xue-Lu Xiong (熊雪露), Shujin Laima (赖马树金), Hui Li (李惠), and Yi Zhou (周毅)
Phys. Rev. Fluids 9, 054608 (2024)
NEW ARTICLE
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.
I. Rubinstein and B. Zaltzman
Phys. Rev. Fluids 9, 053701 (2024)
NEW ARTICLE
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.
Xuan Zhang, Philipp Reiter, Olga Shishkina, and Robert E. Ecke
Phys. Rev. Fluids 9, 053501 (2024)
NEW ARTICLE
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.
Oscar J. Punch, Daniel J. Holland, Andreas Baumann, and Peter Eberhard
Phys. Rev. Fluids 9, 054302 (2024)
EDITORS' SUGGESTION
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.
Xiaofeng Wei et al.
Phys. Rev. Fluids 9, 054003 (2024)
NEW ARTICLE
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.
Qiang Du, Yaguang Xie, Lei Xie, and Ruonan Wang
Phys. Rev. Fluids 9, 053908 (2024)
NEW ARTICLE
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 Re = 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.
L. H. O. Hellström, T. Van Buren, J. C. Vaccaro, and A. J. Smits
Phys. Rev. Fluids 9, 054607 (2024)
NEW ARTICLE
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.
J. J. Taylor-West and A. J. Hogg
Phys. Rev. Fluids 9, 053301 (2024)