| Volume 8, Issue 8 August 2023 | |
Advertisement | Abstract submissions are officially open for the APS March Meeting 2024! Showcase your work to a global audience of physicists, scientists, and students representing 32 APS Units and Committees and explore groundbreaking research from industry, academia, and major labs. Start preparing your abstract and be sure to submit it by October 20. Submit an abstract. | | | | | | Not an APS member? Join today to start connecting with a community of more than 50,000 physicists. | | | | Editors' Suggestion Alexandros T. Oratis, Vincent Bertin, and Jacco H. Snoeijer Phys. Rev. Fluids 8, 083603 (2023) – Published 18 August 2023  | The coalescence of bubbles dissolved in liquids occurs in systems like foams, magma, and various other bubbly flows. Here, we investigate the coalescence of two bubbles of identical size in semidilute aqueous polymer solutions. The rheological properties are very different from those of water; yet, the early-time dynamics of coalescence are not altered by the presence of polymers. Even though the polymers get highly stretched in the azimuthal direction, we find that the resulting hoop force is insufficient to modify the rate of coalescence or the shape of the growing neck. | | | | | | Editors' Suggestion F. Caruso Lombardi, A. Bongarzone, G. A. Zampogna, F. Gallaire, S. Camarri, and P. G. Ledda Phys. Rev. Fluids 8, 083901 (2023) – Published 9 August 2023  | We explore the role of permeability in modifying the vortex shedding past a permeable circular cylinder. The two-dimensional (2D) von Kármán vortex street sets at progressively larger distances from the body and is eventually suppressed, as permeability increases. Using Dynamic Mode Decomposition we perform a linear stability analysis with respect to three-dimensional perturbations of the 2D periodic vortex shedding. We identify a range of permeability in which the shedding remains 2D, at least for the values of Reynolds number considered here; for larger values of permeability, the wake remains steady and 2D. | | | | | | Editors' Suggestion Xiaolong Zhang (张晓龙) and Vadim S. Nikolayev Phys. Rev. Fluids 8, 084002 (2023) – Published 11 August 2023  | A pulsating heat pipe (PHP) is a capillary meandering between hot spot and cooled area filled with a two-phase fluid that oscillates inside it due to evaporation and condensation. We introduce a one-dimensional physical model, the Oscillating Film Thickness model, that incorporates previously overlooked physics related to liquid film deposition, evaporation, and contact line motion. The model more accurately represents the physics of the phenomena without loss of computational efficiency. Improvements in modeling accuracy and computational efficiency are demonstrated for the case of the simplest, single branch PHP. | | | | | | Editors' Suggestion Robert Hunt, Ze Zhao, Eli Silver, Jinhui Yan, Yuri Bazilevs, and Daniel M. Harris Phys. Rev. Fluids 8, 084003 (2023) – Published 22 August 2023  | Drag on a sphere in a steady flow is an important and thoroughly studied problem in fluid dynamics, yet relatively little work includes the effects of a free surface. Through experiments and simulations, we characterize the drag on a sphere partially immersed at an air-water interface as a function of submergence depth. The presence of the free surface can induce drag forces several times greater than the equivalent fully submerged case, with pronounced hysteretic effects strongly influenced by the sphere's wettability. We ascribe the drag increase to an asymmetric pressure loading on the sphere that persists for flows both above and below the minimum capillary-gravity wave speed. | | | | | | Editors' Suggestion D. Saccone, M. De Marchis, B. Milici, and C. Marchioli Phys. Rev. Fluids 8, 084303 (2023) – Published 16 August 2023  | This study examines combined effects of particle inertia, particle aspect ratio, and wall roughness on dynamics of prolate ellipsoidal particles dispersed in turbulent channel flow bounded by rough walls. We use direct numerical simulation of the turbulence and Lagrangian tracking of the particles. The particles spatial distribution within the flow domain and their translational statistics is shown to depend almost exclusively on the combined effect of inertia and wall roughness, with weak aspect ratio effects. These effects are observed in the particle orientation statistics: Longer particles exhibit a stronger tendency to align with the mean flow direction, especially at low inertia. | | | | | | Editors' Suggestion Lingyun Ding and Richard M. McLaughlin Phys. Rev. Fluids 8, 084501 (2023) – Published 2 August 2023  | We study the unsteady diffusion-induced flow in an inclined channel domain, and mixing of a diffusing passive scalar advected by such flows. Diffusion-driven flow is a boundary layer flow due to the combination of gravity and diffusion, existing in density-stratified fluids when gravity is not parallel to the solid boundary. We find that the flow can be either highly oscillatory in space and time, or monotonic depending on the physical parameters. On transient timescales there are situations in which the effective mixing is reduced below the bare molecular diffusivity. Such flows are relevant for applications including solute evolution in rock fissures and also in microfluidics. | | | | | | Letter Kartik P. Iyer Phys. Rev. Fluids 8, L082601 (2023) – Published 11 August 2023  | The dissipation of kinetic energy in a turbulent flow is controlled by the competition between the random pushing and pulling of fluid parcels. If the pushing and pulling motions average each other out with increasing turbulence intensity, then the average dissipation must decay and energy will be conserved in the inviscid limit. This work highlights this pivotal dependence of the energy dissipation rate on the small-scale motions in fluid turbulence. | | | | | | Complex and Non-Newtonian Fluids | A. Kordalis, D. Pema, S. Androulakis, Y. Dimakopoulos, and J. Tsamopoulos Phys. Rev. Fluids 8, 083301 (2023) – Published 9 August 2023  | We investigate the pair interaction of equal-size, tandem bubbles rising in yield stress fluids with elasticity. This configuration manifests intense attractive dynamics and conforms with experimental reports that, in such materials, a bubble tends to follow the path of a preceding one. We demonstrate that the reason is that the solid-like behavior of the material preserves stresses generated by the passage of the leading bubble and makes the material "softer" for the trailing one. We conduct an extensive parametric study, on the geometric features such as the bubble radius and the initial separation distance, and on the material properties. | | | | | | Compressible and Rarefied Flows, Kinetic Theory | Ryan M. McMullen, Michael C. Krygier, John R. Torczynski, and Michael A. Gallis Phys. Rev. Fluids 8, 083401 (2023) – Published 28 August 2023  | Turbulent boundary layers on reentry vehicles may be modified by roughness, permeability, and noncontinuum effects induced by the fibrous thermal-protection-system (TPS) material coating its surface. To investigate these effects, we perform molecular-gas-dynamics (MGD) simulations of turbulent Couette flow over a substrate inspired by TPS materials. We find that rarefaction within the substrate can significantly increase its permeability, while in the free portion of the channel, we observe surprisingly good agreement between our MGD simulations and the Navier-Stokes equations, even when the local Knudsen number approaches the value typically associated with breakdown of the continuum assumption. | | | | | | Robert Hartmann, Guru S. Yerragolam, Roberto Verzicco, Detlef Lohse, and Richard J. A. M. Stevens Phys. Rev. Fluids 8, 083501 (2023) – Published 28 August 2023  | Moderate rotation is able to enhance the heat transport in (rotating) Rayleigh-Bénard convection. While the heat transport can significantly exceed the nonrotating value for Rayleigh numbers Ra≲5×108, no or only little enhancement remains at larger Ra. Here, we aim to identify the reason for the vanishing heat transport enhancement and its different behavior towards large Ra: How is the loss of enhancement related to the onset of geostrophic turbulence? What role does rotation-induced shearing at the plates play in this context? | | | | | | Drops, Bubbles, Capsules, and Vesicles | Peng Xu, Bo Li, Zibo Ren, Shuhong Liu, and Zhigang Zuo Phys. Rev. Fluids 8, 083601 (2023) – Published 2 August 2023  | In engineering where cavitation occurs, pressure around the cavitation bubble is usually distributed nonuniformly. We focus on the intermediate jet formed during nonspherical collapse of a buoyant cavitation bubble near a rigid vertical boundary, where pressure gradients due to gravity and the rigid boundary are mutually perpendicular. A series of jets with different directions and intensities are obtained from experiment. Jet directions and scaling laws of the dimensionless jet velocity versus combinations of pressure anisotropy parameters are found. The results provide additional information on nonspherical cavitation bubble dynamics under the simultaneous influence of multiple factors. | | | | | | Natasha Singh and Vivek Narsimhan Phys. Rev. Fluids 8, 083602 (2023) – Published 16 August 2023  | When two droplets come close together to coalesce, a thin liquid film forms between the droplets. The drainage of this film alters the critical conditions under which coalescence occurs. In this study, we explore how the interfacial surface shear and dilational viscosity affect the thin film formation and drainage time in a head-on collision between two droplets. We model the surface rheology of the droplet using the Boussinesq–Scriven constitutive relationship for a Newtonian interface. | | | | | | Editors' Suggestion Alexandros T. Oratis, Vincent Bertin, and Jacco H. Snoeijer Phys. Rev. Fluids 8, 083603 (2023) – Published 18 August 2023 | The coalescence of bubbles dissolved in liquids occurs in systems like foams, magma, and various other bubbly flows. Here, we investigate the coalescence of two bubbles of identical size in semidilute aqueous polymer solutions. The rheological properties are very different from those of water; yet, the early-time dynamics of coalescence are not altered by the presence of polymers. Even though the polymers get highly stretched in the azimuthal direction, we find that the resulting hoop force is insufficient to modify the rate of coalescence or the shape of the growing neck. | | | | | | Orr Avni and Yuval Dagan Phys. Rev. Fluids 8, 083604 (2023) – Published 30 August 2023  | Intricate connections involving vortical flow patterns, droplet relaxation times, drag forces, and transport processes are examined using a Lagrangian particle tracking approach. We focus on mass transport and phase transition in droplets within Burgers vortices, capturing the essence of small-scale structures within turbulent flows. Thermodynamic gradients generate complex dynamics; droplets may stabilize around the vortex, revealing a periodic solution only when a high pressure drop generates a condensation core. This dynamical periodicity may suggest droplet clustering induced by phase change, while the emergence of the condensation region reveals a distinct bifurcation point. | | | | | | Orr Avni and Yuval Dagan Phys. Rev. Fluids 8, 083605 (2023) – Published 30 August 2023  | This second part of a paper series extends the previous model to account for the role of heat transfer in the equilibrium and transient response of droplet-vortex systems, serving as a case model for a broader range of interactions between droplets and vortical flows. The presented scaling analysis elucidates the coupling between heat and mass transport mechanism and uncovers the timescale characteristic of each within vortical structures. We analyze the extent to which nonlinear transport processes play a significant role in the droplet's dynamic response. This analysis may serve as an estimation for the thermodynamic conditions in which the incorporation of nonlinear effects is substantial. | | | | | | Electrokinetic Phenomena, Electrohydrodynamics, and Magnetohydrodynamics | Calum S. Skene and Steven M. Tobias Phys. Rev. Fluids 8, 083701 (2023) – Published 28 August 2023  | Our paper investigates the modification of the Lagrangian statistics of a fluid flow by a magnetic field undergoing dynamo action, for a family of flows generated by spatially periodic oscillating-in-time forcings. A Floquet stability analysis shows that an exact periodic solution to these flows becomes unstable, leading to a turbulent fluid flow regime. By calculating the finite-time-Lyapunov-exponents we can then characterize the amount of stretching and chaos present in these flows. In all cases considered, we show that the amount of chaos in the saturated dynamo flow is reduced from that of the underlying turbulent flow, providing insight into how these dynamos saturate. | | | | | | J. Galen Wang, Daniel R. Ladiges, Ishan Srivastava, Sean P. Carney, Andy J. Nonaka, Alejandro L. Garcia, and John B. Bell Phys. Rev. Fluids 8, 083702 (2023) – Published 29 August 2023  | We investigate the role of steric effects on induced-charge electro-osmosis, focusing on flow field and charge distribution. Steric effects are crucial mesoscale phenomena, but they are either neglected or overly simplified in previous theoretical and computational studies. Using a hybrid Eulerian-Lagrangian method, our simulations highlight the importance of the steric effects, which lead to intriguing characteristics at strong electric fields that have not been captured by the traditional continuum method, including a suppression of velocity scaling and the overcharging of co-ions to the surface charge. | | | | | | Zhao-Bo Wang, Long Chen, Yan-Wu Cao, Chun-Xu Ke, Juan-Cheng Yang, and Ming-Jiu Ni Phys. Rev. Fluids 8, 083703 (2023) – Published 30 August 2023  | Numerical verification is presented of Davidson's theoretical proposal that the angular momentum parallel to the magnetic field of a single vortex is conserved whereas the perpendicular angular momentum decays exponentially during a free-decay evolution. Theoretical scaling laws for the linear process and the nonlinear process of a single MHD vortex decay are given. It is found that the initial linear phase of a single MHD vortex decay characterized by the dominance of the Lorentz force over the inertial force exists locally. However, the whole evolution is closer to the global nonlinear behavior of a single vortex decay, for which the viscous dissipation is almost equal to the Joule dissipation. | | | | | | Instability, Transition, and Control | Editors' Suggestion F. Caruso Lombardi, A. Bongarzone, G. A. Zampogna, F. Gallaire, S. Camarri, and P. G. Ledda Phys. Rev. Fluids 8, 083901 (2023) – Published 9 August 2023 | We explore the role of permeability in modifying the vortex shedding past a permeable circular cylinder. The two-dimensional (2D) von Kármán vortex street sets at progressively larger distances from the body and is eventually suppressed, as permeability increases. Using Dynamic Mode Decomposition we perform a linear stability analysis with respect to three-dimensional perturbations of the 2D periodic vortex shedding. We identify a range of permeability in which the shedding remains 2D, at least for the values of Reynolds number considered here; for larger values of permeability, the wake remains steady and 2D. | | | | | | Ashish Mishra, George Mamatsashvili, and Frank Stefani Phys. Rev. Fluids 8, 083902 (2023) – Published 17 August 2023  | Magnetorotational instability (MRI) is the most likely mechanism driving angular momentum transport in astrophysical disks. However, there is no conclusive experimental evidence for MRI, despite many attempts to find it. The planned DRESDYN-MRI experiments are a new effort which use a magnetized Taylor-Couette flow of liquid sodium that mimics an accretion disk. We numerically study the nonlinear evolution and saturation of MRI and analyze its scaling behavior for the DRESDYN-MRI device. The obtained scaling laws with Reynolds number, yielding the magnitudes of velocity and magnetic field perturbations expected in these experiments, will be crucial for identifying MRI in the laboratory. | | | | | | Elizabeth K. Benitez, Matthew P. Borg, Pedro Paredes, Steven P. Schneider, and Joseph S. Jewell Phys. Rev. Fluids 8, 083903 (2023) – Published 22 August 2023  | Compression corners are commonly present along aircraft, such as at control surfaces, and can cause shock/boundary-layer interactions when the vehicle moves at supersonic or hypersonic speeds. By generating a separation bubble at the corner, a shear layer is present in the flow, which can potentially amplify instabilities, leading to a boundary-layer transition downstream of reattachment. We show, through experiments conducted under low-disturbance Mach-6 flow, the amplification of such a shear-layer instability by comparing measurements from two cone-cylinder-flare geometries with computations of the same. | | | | | | Chengyun Wang, Peng Yu, and Haibo Huang Phys. Rev. Fluids 8, 083904 (2023) – Published 22 August 2023  | We employ a single-step Deep Reinforcement Learning (DRL) algorithm to optimize the spatial location and length of a downstream splitter plate, aimed at suppressing vortex shedding behind a cylinder. Contrary to common sense, positioning the splitter plate laterally rather than directly in the posterior of the cylinder can make a greater influence on the stability of the entire flow field, even with a shorter length. By integrating DRL techniques, stability analysis via dynamic mode decomposition (DMD), and comparisons with Bayesian optimization (BO), the study highlights the potential of this DRL algorithm for advanced optimization in fluid dynamics. | | | | | | Interfacial Phenomena and Flows | Rebecca A. McKinlay, Alexander W. Wray, and Stephen K. Wilson Phys. Rev. Fluids 8, 084001 (2023) – Published 11 August 2023  | We use a combination of analytical and numerical techniques to give a complete description of the late-time draining of a thin liquid film on the outer surface of a horizontal cylinder. In this asymptotic limit three regions of qualitatively different behavior emerge, namely a draining region on the upper part of the cylinder and a pendant-drop region on the lower part of the cylinder joined by a narrow inner region in which the film has a surprisingly complicated capillary-ripple structure consisting of an infinite sequence of alternating dimples and ridges. | | | | | | Editors' Suggestion Xiaolong Zhang (张晓龙) and Vadim S. Nikolayev Phys. Rev. Fluids 8, 084002 (2023) – Published 11 August 2023 | A pulsating heat pipe (PHP) is a capillary meandering between hot spot and cooled area filled with a two-phase fluid that oscillates inside it due to evaporation and condensation. We introduce a one-dimensional physical model, the Oscillating Film Thickness model, that incorporates previously overlooked physics related to liquid film deposition, evaporation, and contact line motion. The model more accurately represents the physics of the phenomena without loss of computational efficiency. Improvements in modeling accuracy and computational efficiency are demonstrated for the case of the simplest, single branch PHP. | | | | | | Editors' Suggestion Robert Hunt, Ze Zhao, Eli Silver, Jinhui Yan, Yuri Bazilevs, and Daniel M. Harris Phys. Rev. Fluids 8, 084003 (2023) – Published 22 August 2023 | Drag on a sphere in a steady flow is an important and thoroughly studied problem in fluid dynamics, yet relatively little work includes the effects of a free surface. Through experiments and simulations, we characterize the drag on a sphere partially immersed at an air-water interface as a function of submergence depth. The presence of the free surface can induce drag forces several times greater than the equivalent fully submerged case, with pronounced hysteretic effects strongly influenced by the sphere's wettability. We ascribe the drag increase to an asymmetric pressure loading on the sphere that persists for flows both above and below the minimum capillary-gravity wave speed. | | | | | | Laminar and Viscous Flows | Yang Liu, Yifeng Zhu, and Changhui Liu Phys. Rev. Fluids 8, 084101 (2023) – Published 17 August 2023  | The scaling method is used to study the transient natural convection boundary layer flow, and the curvature effect is investigated. Important scaling laws, such as boundary layer thickness δt and characteristic velocity umz of the transient and steady states and cut-off time of the initial growth are determined in the explicit form, where the curvature effect is accurately described by the proposed dimensionless coefficient Ψ′(A). The present explicit laws provide clearer physical interpretation, make the scaling laws much easier to utilize, and facilitate a better understanding of the underlying physical phenomena governing the curved boundary layer flow. | | | | | | Aysan Razzaghi and Arun Ramachandran Phys. Rev. Fluids 8, 084201 (2023) – Published 28 August 2023  | We present a strategy to use hydrodynamic force in a six-port microfluidic channel to steer two drops towards collision in an extensional flow. By implementing an analytical solution in the control loop, the flow rates that are required to steer the drops toward their respective target points can be determined using a single control parameter. This parameter is a dimensionless time scale that can manipulate the drops either by engaging all six ports to create a flow field with two stagnation points, or by deactivating some of the ports and creating a linear extensional flow. | | | | | | Multiphase, Granular, and Particle-Laden Flows | M. Hausmann, F. Evrard, and B. van Wachem Phys. Rev. Fluids 8, 084301 (2023) – Published 11 August 2023  | In this paper, a new modeling strategy for large eddy simulations (LES) of particle-laden turbulent flows is proposed, which takes the influence of the subgrid-scale fluid velocity on the particle transport and the turbulence modulation by the particles into account. The modeling combines an enrichment of the LES with subgrid-scale fluid velocity and a subgrid-scale model based on a transport equation for the subgrid-scale kinetic energy. The model improves the particle clustering and the kinetic energy spectrum of homogeneous isotropic turbulence laden with two-way coupled particles compared to standard LES. | | | | | | Antonio Pol, Riccardo Artoni, and Patrick Richard Phys. Rev. Fluids 8, 084302 (2023) – Published 14 August 2023  | Using particle-based simulations, we study the wall friction weakening in three-dimensional dense, confined granular flows made of shape anisotropic particles. We show how the effective wall friction is affected by both particle shape and flow pattern. Then, we propose a new scaling law for the friction mobilization at the walls which is based on a balance between sliding and rolling motion of the particles. This study highlights the importance of angular motion of the particles for the understanding of granular flows at flat boundaries and may reignite the debate about the relevant variables in theories aiming to capture and predict the behavior of dense and confined granular flows. | | | | | | Editors' Suggestion D. Saccone, M. De Marchis, B. Milici, and C. Marchioli Phys. Rev. Fluids 8, 084303 (2023) – Published 16 August 2023 | This study examines combined effects of particle inertia, particle aspect ratio, and wall roughness on dynamics of prolate ellipsoidal particles dispersed in turbulent channel flow bounded by rough walls. We use direct numerical simulation of the turbulence and Lagrangian tracking of the particles. The particles spatial distribution within the flow domain and their translational statistics is shown to depend almost exclusively on the combined effect of inertia and wall roughness, with weak aspect ratio effects. These effects are observed in the particle orientation statistics: Longer particles exhibit a stronger tendency to align with the mean flow direction, especially at low inertia. | | | | | | Xiaohui Meng and Ewe-Wei Saw Phys. Rev. Fluids 8, 084304 (2023) – Published 18 August 2023  | In turbulence, particle collision-and-coagulation significantly reduce the number of particle pairs at separation distances closer than about 2.5 times particle diameter. This results in a noticeable decrease in the particle radial distribution function (RDF) compared to when collisions are absent. By examining the changes in the RDF and its relationship with particle and turbulence parameters, we can see how these physical factors influence the RDF. | | | | | | Himanshu Dave and M. Houssem Kasbaoui Phys. Rev. Fluids 8, 084305 (2023) – Published 21 August 2023  | We show that significant drag reduction can be achieved in a turbulent channel flow using appropriately scaled mono-disperse particles. We show that drag-reducing particles form very long ropes along the channel wall. These particle ropes interfere with the near-wall turbulence regeneration mechanisms, which causes partial re-laminarization of the flow and significant reduction of skin-friction drag. | | | | | | Editors' Suggestion Lingyun Ding and Richard M. McLaughlin Phys. Rev. Fluids 8, 084501 (2023) – Published 2 August 2023 | We study the unsteady diffusion-induced flow in an inclined channel domain, and mixing of a diffusing passive scalar advected by such flows. Diffusion-driven flow is a boundary layer flow due to the combination of gravity and diffusion, existing in density-stratified fluids when gravity is not parallel to the solid boundary. We find that the flow can be either highly oscillatory in space and time, or monotonic depending on the physical parameters. On transient timescales there are situations in which the effective mixing is reduced below the bare molecular diffusivity. Such flows are relevant for applications including solute evolution in rock fissures and also in microfluidics. | | | | | | Pratyaksh Karan, Uddipta Ghosh, Fabian Brau, Yves Méheust, and Tanguy Le Borgne Phys. Rev. Fluids 8, 084502 (2023) – Published 31 August 2023  | Reaction fronts are regions in a flow field where two solutes, brought together by advection and dispersion, mix and react. Often, injection of one solute into a porous reservoir of the other manifests in a spherical reaction front, the dynamics of which is addressed here. In a porous medium, mixing between the two solutes is greatly enhanced because of hydrodynamic dispersion, resulting in a more advanced position of the front, while the rate of reaction also gets augmented significantly during the initial transient regimes. We show that when dispersion is sufficiently strong, these early enhancements are also maintained at larger times, when the front inevitably reaches a stationary state. | | | | | | Simran Singh Panesar, Hao Xia, and Martin Passmore Phys. Rev. Fluids 8, 084601 (2023) – Published 9 August 2023  | Bistability is of significant interest for ground vehicle drag reduction and reduced order modelling of simulated flows. For many bluff bodies, an oblique, asymmetric shedding mode persists with a transient parallel, symmetric state. Base pressure and particle image velocimetry measurements are made in the bistable wake of a surface mounted geometry of semi-circular cross section (half-axisymmetric) at ReD=3.2×105. Using proper orthogonal decomposition and wavelet analysis, we find that bifurcation to an opposing symmetry breaking state is tied to reversal of an oblique mode at the vortex shedding frequency. | | | | | | Mogeng Li, Woutijn J. Baars, Ivan Marusic, and Nicholas Hutchins Phys. Rev. Fluids 8, 084602 (2023) – Published 21 August 2023  | We investigate the underlying physics behind the change in amplitude modulation coefficient in noncanonical wall-bounded flows in the framework of the inner-outer interaction model (IOIM). An analytical relationship between the amplitude modulation coefficient and IOIM parameters is derived, which is shown to capture the increasing trend of the amplitude modulation coefficient with an increasing Reynolds number in a smooth-wall dataset. This relationship is then applied to classify and interpret the results of a turbulent boundary layer after a rough-to-smooth change in this work, as well as other noncanonical flow in the literature. | | | | | | Weijun Yin, Shancong Tao, Koji Nagata, Yasumasa Ito, Yasuhiko Sakai, and Yi Zhou Phys. Rev. Fluids 8, 084603 (2023) – Published 24 August 2023  | The coherent structures in a self-similar axisymmetric turbulent wake are orderly distributed and also regularly organized. There is an intrinsic connection between the self-similar distributions of the one-point statistics and the spatial distribution of the coherent structures. We confirm the well-known assertion that coherent structures are "the sinews and muscles of fluid motions". | | | | | | Chenyu Wu and Yufei Zhang Phys. Rev. Fluids 8, 084604 (2023) – Published 24 August 2023  | Data-driven Reynolds averaged Navier-Stokes (RANS) turbulence models for separated flows based on black-box machine learning models have been widely researched in recent years. However, they often lack generalizability and interpretability. In this work, field inversion and symbolic regression (FISR) are used to develop an interpretable and generalizable data-driven RANS turbulence model. The proposed turbulence model shows good accuracy in various test cases that are completely distinct from its training set. | | | | | | Sugan Durai Murugan and Samriddhi Sankar Ray Phys. Rev. Fluids 8, 084605 (2023) – Published 28 August 2023  | The long-time solutions of the Galerkin-truncated, three-dimensional, incompressible Euler equations relax to an absolute equilibrium state. We uncover the mechanism that triggers thermalization in physical space and conclude with a numerical prescription to suppress the oscillations that precede onset of thermalization in numerical simulations of the Euler equation. | | | | | | Yoshiki Sakurai and Takashi Ishihara Phys. Rev. Fluids 8, 084606 (2023) – Published 28 August 2023  | Direct numerical simulations (DNS) of compressible isothermal turbulence (CIT) at turbulent Mach number around 0.3 in a periodic box with the number of grid points and the Taylor microscale Reynolds number up to 4096^3 and 853 are conducted using an 8th-order compact finite difference scheme. The DNS results show that the solenoidal component of the energy spectrum and the solenoidal dissipation rate obtained from CIT agree well with those from incompressible turbulence when normalized by solenoidal quantities. Results with high spatial resolution show that the dilatational component of the energy spectrum for CIT exhibits a power law at high wavenumbers due to the appearance of shocklets. | | | | | | Hamidreza Anbarlooei, Fabio Ramos, and Daniel O. A. Cruz Phys. Rev. Fluids 8, 084607 (2023) – Published 28 August 2023  | This study offers a detailed description of momentum exchange in turbulent boundary layer flows at extreme Reynolds numbers. We introduce a new power-law formula for skin-friction, revealing insights into the boundary layer's asymptotic thickness. Our findings align with experimental data, suggesting a universal transition in wall-bounded flows at high Reynolds numbers. | | | | | | Wave Dynamics, Free Surface Flows, Stratified, and Rotating Flows | Zakhar V. Makridin, Alexander K. Khe, Ilias N. Sibgatullin, and Eugeny V. Ermanyuk Phys. Rev. Fluids 8, 084801 (2023) – Published 4 August 2023  | We study internal wave focusing in a trapezoidal domain with one moving boundary. We construct the analytical solution in the linear inviscid formulation and compare it against the results of direct numerical simulations. It is shown that the nested structure of wave beams in the ideal-fluid solution is consistent with the peculiarities of the wave-beam profiles obtained in weakly viscous numerical simulations performed in a wide range of Stokes numbers. | | | | | | Alice Marcotte, François Gallaire, and Alessandro Bongarzone Phys. Rev. Fluids 8, 084802 (2023) – Published 21 August 2023  | We report robust experimental evidence of the bistability of sloshing waves in circular cylindrical containers following planar and time-harmonic elliptic orbits. Specifically, we observed for the first time the counterintuitive existence of stable counter-swirling waves. Such novel experimental findings support previous theoretical studies and are here further rationalized by an asymptotic analysis, which shows that this archetypal resonant sloshing system can be well described by 4 degrees-of-freedom only. | | | | | | Young R. Yi and Jeffrey R. Koseff Phys. Rev. Fluids 8, 084803 (2023) – Published 23 August 2023  | Large scale ocean simulations employ eddy viscosities and diffusivities to represent the irreversible mixing of momentum and scalars due to unresolved scales of motion. These closures often require a prescription of the ratio of the vertical buoyancy flux to the rate of turbulence production (i.e., mixing efficiency). In this paper, we demonstrate that this ratio is strongly sensitive to the turbulence generation mechanism by considering the Reynolds stress and buoyancy flux budgets as a function of the turbulent Froude number. | | | | | | Zhi Zhou, Petia M. Vlahovska, and Michael J. Miksis Phys. Rev. Fluids 8, 089901 (2023) – Published 28 August 2023 | | | | |
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