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Enhanced recovery caused by nonlinear dynamics in the wake of a floating offshore wind turbine J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Thomas Messmer, Michael Hölling, Joachim Peinke
An experimental study in a wind tunnel is presented to explore the wake of a floating wind turbine subjected to harmonic side-to-side and fore–aft motions under laminar inflow conditions. The wake recovery is analysed as a function of the frequency of motion $f_p$ , expressed by the rotor-based Strouhal number, $St = f_p D / U_{\infty }$ ( $D$ is the rotor diameter, $U_{\infty }$ the inflow wind speed)
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Langmuir turbulence in suspended kelp farms J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Tong Bo, James C. McWilliams, Chao Yan, Marcelo Chamecki
This study investigates the influence of suspended kelp farms on ocean mixed layer hydrodynamics in the presence of currents and waves. We use the large eddy simulation method, where the wave effect is incorporated by solving the wave-averaged equations. Distinct Langmuir circulation patterns are generated within various suspended farm configurations, including horizontally uniform kelp blocks and
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Reactive control of velocity fluctuations using an active deformable surface and real-time PIV J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Findlay McCormick, Bradley Gibeau, Sina Ghaemi
This study demonstrates an experimental realization of turbulence control strategies previously explored by Choi et al. (J. Fluid Mech., vol. 262, 1994, pp. 75–110) through numerical simulations. To conduct the experiments, a deformable surface with a streamwise array of 16 independently controlled actuators was developed. A real-time particle image velocimetry (RT-PIV) system was also created for
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The structure of turbulence in unsteady flow over urban canopies J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Weiyi Li, Marco G. Giometto
The topology of turbulent coherent structures is known to regulate the transport of energy, mass and momentum in the atmospheric boundary layer (ABL). While previous research has primarily focused on characterizing the structure of turbulence in stationary ABL flows, real-world scenarios frequently deviate from stationarity, giving rise to nuanced and poorly understood changes in the turbulence geometry
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Characterization of partial wetting by CMAS droplets using multiphase many-body dissipative particle dynamics and data-driven discovery based on PINNs J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Elham Kiyani, Mahdi Kooshkbaghi, Khemraj Shukla, Rahul Babu Koneru, Zhen Li, Luis Bravo, Anindya Ghoshal, George Em Karniadakis, Mikko Karttunen
The molten sand that is a mixture of calcia, magnesia, alumina and silicate, known as CMAS, is characterized by its high viscosity, density and surface tension. The unique properties of CMAS make it a challenging material to deal with in high-temperature applications, requiring innovative solutions and materials to prevent its buildup and damage to critical equipment. Here, we use multiphase many-body
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Interplay of scales during the spatial evolution of energy-containing motions in wall-bounded turbulent flows J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Ezhilsabareesh Kannadasan, Callum Atkinson, Julio Soria
This article extends the previous investigation of the spatial evolution of energy-containing motions in wall-bounded turbulent flows (Kannadasan et al., J. Fluid Mech., vol. 955, 2023, R1) by examining their scale-interactions through spectral analysis based on the spanwise scale decomposition of turbulent kinetic energy and the Reynolds stress transport equation. The energy-containing motions located
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Cylinder flow and noise control by active base blowing J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Reza Maryami, Yu Liu
An extensive experimental investigation was undertaken to control the flow and noise characteristics influenced by vortex shedding from a circular cylinder by implementing air blowing at the base of the cylinder. The study synchronised near-field pressure and far-field noise measurements with the wake velocity field to understand the noise reduction mechanism of base blowing. Surface pressure fluctuations
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Mechanism for axial pattern formation of concentrated suspension in a horizontal rotating cylinder J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 Sudarshan Konidena, Bernhard Vowinckel, Ryohei Seto, K. Anki Reddy, Anugrah Singh
We have performed numerical simulations to investigate the phenomenon of axial pattern formation exhibited by a non-neutrally buoyant concentrated suspension. Continuum modelling of the concentrated suspension is done using the suspension balance model to identify the underlying mechanism of the phenomenon. We demonstrate that axial concentration variations become amplified to axial bands owing to
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Peeling fingers in an elastic Hele-Shaw channel J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-16 João V. Fontana, Callum Cuttle, Draga Pihler-Puzović, Andrew L. Hazel, Anne Juel
Using experiments and a depth-averaged numerical model, we study instabilities of two-phase flows in a Hele-Shaw channel with an elastic upper boundary and a non-uniform cross-section prescribed by initial collapse. Experimentally, we find increasingly complex and unsteady modes of air-finger propagation as the dimensionless bubble speed $Ca$ and level of collapse are increased, including pointed fingers
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Simulating the rheology of dense suspensions using pairwise formulation of contact, lubrication and Brownian forces J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-15 Xuan Li, John R. Royer, Christopher Ness
Dense suspensions of solid particles in viscous liquid are ubiquitous in both industry and nature, and there is a clear need for efficient numerical routines to simulate their rheology and microstructure. Particles of micron size present a particular challenge: at low shear rates, colloidal interactions control their dynamics while at high rates, granular-like contacts dominate. While there are established
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Low-order modelling of three-dimensional surface waves in liquid film flow on a rotating disk J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-15 Dong Ju Kim, Daegyoum Kim
Using low-dimensional numerical simulations, we investigate the characteristics of complex and three-dimensional surface waves in a liquid film flowing over a rotating disk, focusing on large flow rates from a nozzle. Existing integral boundary layer (IBL) models, which are based on spatially averaged variables along the direction normal to the disk surface, have primarily focused on the formation
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On the dynamics and wakes of a freely settling Platonic polyhedron in a quiescent Newtonian fluid J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-15 Guodong Gai, Anthony Wachs
We investigate systematically the free settling of a single Platonic polyhedron in an unbounded domain filled with an otherwise quiescent Newtonian fluid. We consider a particle–fluid density mimicking a rock in water. Five Platonic polyhedrons of increasing sphericity are studied for a range of Galileo numbers $10 \leqslant \mathcal {G}a \leqslant 300$ . We construct a regime map in the parameter
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Aeroacoustics of a ducted fan ingesting an adverse pressure gradient boundary layer J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-15 Feroz Ahmed, Ismaeel Zaman, Djamel Rezgui, Mahdi Azarpeyvand
The aeroacoustics of a boundary layer ingesting (BLI) ducted fan is investigated experimentally. The study examines a ducted fan immersed in an adverse streamwise pressure gradient turbulent boundary layer developed over a curved wall. Aeroacoustics measurements indicate that the noise from the BLI ducted fan results from a complex interaction among the fan, duct and the incoming boundary layer. The
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Different scenarios in sloshing flows near the critical filling depth J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 A. Bardazzi, C. Lugni, O.M. Faltinsen, D. Durante, A. Colagrossi
In the present paper, the sloshing flow in a cuboid tank forced to oscillate horizontally is investigated with both experimental and numerical approaches. The filling depth chosen is $h/L=0.35$ (with h the water depth and L the tank height), which is close to the critical depth. According to Tadjbakhsh & Keller (J. Fluid Mech., vol. 8, issue 3, 1960, pp. 442–451), as the depth passes through this critical
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Electromagnetically driven flow in unsupported electrolyte layers: lubrication theory and linear stability of annular flow J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Andrey Pototsky, Sergey A. Suslov
We consider a thin horizontal layer of a non-magnetic electrolyte containing a bulk solution of salt and carrying an electric current. The layer is bounded by two deformable free surfaces loaded with an insoluble surfactant and is placed in a vertical magnetic field. The arising Lorentz force drives the electrolyte in the plane of the layer. We employ the long-wave approximation to derive general two-dimensional
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The dynamics of fibres dispersed in viscoelastic turbulent flows J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 M.S. Aswathy, Marco Edoardo Rosti
This study explores the dynamics of finite-size fibres suspended freely in a viscoelastic turbulent flow. For a fibre suspended in Newtonian flows, two different flapping regimes were identified by Rosti et al. (Phys. Rev. Lett., vol. 121, issue 4, 2018, 044501): one dominated by time scales from the flow, and another dominated by time scales associated with its natural frequency. We explore in this
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Departure from the statistical equilibrium of large scales in forced three-dimensional homogeneous isotropic turbulence J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Mengjie Ding, Jin-Han Xie, Jianchun Wang
We study the statistically steady states of the forced dissipative three-dimensional homogeneous isotropic turbulence at scales larger than the forcing scale in real separation space. The probability density functions (p.d.f.s) of longitudinal velocity difference at large separations are close to, but deviate from, Gaussian, measured by their non-zero odd parts. The analytical expressions of the third-order
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Turbulence induced by a swarm of rising bubbles from coarse-grained simulations J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Rémi Zamansky, Florian Le Roy De Bonneville, Frédéric Risso
We performed numerical simulations of a homogeneous swarm of bubbles rising at large Reynolds number, $Re=760$ , with volume fractions ranging from 1 % to 10 %. We consider a simplified model in which the interfaces are not resolved, but which allows us to simulate flows with a large number of bubbles and to emphasize the interactions between bubble wakes. The liquid phase is described by solving,
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On the low-frequency flapping motion in flow separation J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Xingjun Fang, Zhan Wang
Transitional separating flow induced by a rectangular plate subjected to uniform incoming flow at Reynolds number (based on the incoming velocity and half plate height) 2000 is investigated using direct numerical simulation. The objective is to unveil the long-lasting mystery of low-frequency flapping motion (FM) in flow separation. At a fixed streamwise-vertical plane or from the perspective of previous
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Emergence of a hexagonal pattern in shear-thickening suspensions under orbital oscillations J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Li-Xin Shi, Meng-Fei Hu, Song-Chuan Zhao
A dense particle suspension under shear may lose its uniform state to large local density and stress fluctuations, which challenge the mean-field description of the system. Here, we explore the novel dynamics of a non-Brownian suspension under orbital oscillations, where localized density waves along the flow direction appear beyond an excitation frequency threshold and self-organize into a hexagonal
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Inertial coalescence of drops with some viscosity J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Edward Beaty, John R. Lister
When two fluid drops touch, they coalesce due to surface tension. At early times, there is only a relatively small fluid bridge joining the drops. An asymptotic solution is presented for an inertial regime of early-time coalescence, in which inertial forces balance surface tension at leading order. It is demonstrated that viscosity nevertheless has a leading-order effect. Radial momentum is created
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Wave front perturbation effect on the variability of monopile wave impact loads J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Arefhossein Moalemi, Henrik Bredmose, Trygve Kristiansen, Fabio Pierella
The slamming wave force and pressure variabilities for monopile wave impacts are studied as functions of wave breaking shape and transverse perturbations on the breaking wave front. The impacting wave topology is characterized as slosh, flip-through, $\varOmega$ , overturning and fully broken. Fifty test repetitions are conducted for each type of wave impact to assess the variability of force impulse
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Stable three-dimensional vortex families consistent with Jovian observations including the Great Red Spot J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Aidi Zhang, Philip S. Marcus
Detailed observations of the velocities of Jovian vortices exist at only one height in the atmosphere, so their vertical structures are poorly understood. This motivates this study that computes stable three-dimensional, long-lived planetary vortices that satisfy the equations of motion. We solve the anelastic equations with a high-resolution pseudo-spectral method using the observed Jovian atmospheric
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Data-driven state-space and Koopman operator models of coherent state dynamics on invariant manifolds J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 C. Ricardo Constante-Amores, Michael D. Graham
The accurate simulation of complex dynamics in fluid flows demands a substantial number of degrees of freedom, i.e. a high-dimensional state space. Nevertheless, the swift attenuation of small-scale perturbations due to viscous diffusion permits in principle the representation of these flows using a significantly reduced dimensionality. Over time, the dynamics of such flows evolves towards a finite-dimensional
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Direct numerical simulations of microlayer formation during heterogeneous bubble nucleation J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 M. Saini, X. Chen, S. Zaleski, D. Fuster
In this article, we present direct numerical simulation results for the expansion of spherical cap bubbles attached to a rigid wall due to a sudden drop in the ambient pressure. The critical pressure drop beyond which the bubble growth becomes unstable is found to match well with the predictions from classical theory of heterogeneous nucleation imposing a quasi-static bubble evolution. When the pressure
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A comprehensive study on the roles of viscosity and heat conduction in shock waves J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Qingbo Zhu, You Wu, Wenyuan Zhou, Qingchun Yang, Xu Xu
Shock waves are of great interest in many fields of science and engineering, but the mechanisms of their formation, maintenance and dissipation are still not well understood. While all transport processes existing in a shock wave contribute to its compression and irreversibility, they are not of equal importance. To figure out the roles of viscosity and heat conduction in shock transition, the existence
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Evolution of wind-induced wave groups in water of finite depth J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-12 Montri Maleewong, Roger Grimshaw
The generation of water waves by wind is a fundamental and much-studied problem of scientific and operational concern. One mechanism that has obtained a wide degree of acceptance and use is the Miles air shear flow instability theory in which water waves grow due to energy transfer from the air at a critical level where the wave phase speed matches the wind speed. In this paper we revisit and extend
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New momentum integral equation applicable to boundary layer flows under arbitrary pressure gradients J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-11 Tie Wei, Zhaorui Li, Yanxing Wang
By incorporating the traditionally overlooked advective term in the wall-normal momentum equation, a new momentum integral equation is developed for two-dimensional incompressible turbulent boundary layers under arbitrary pressure gradients. The classical Kármán's integral arises as a special instance of the new momentum integral equation when the pressure gradient is weak. The new momentum integral
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Fluid–structure–surface interaction of a flexibly mounted pitching and plunging flat plate in proximity to the free surface J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-11 Hadi Samsam-Khayani, Banafsheh Seyed-Aghazadeh
This experimental study investigates the fluid–structure–surface interactions of a flexibly mounted rigid plate in axial flow, focusing on flow-induced vibration (FIV) response and vortex dynamics of the system within a reduced velocity range of $U^*=0.29\unicode{x2013}8.73$ , corresponding to a Reynolds number range of $Re=518\unicode{x2013}15\,331$ . The plate, with one and two degrees of freedom
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Turbulent flows over porous lattices: alteration of near-wall turbulence and pore-flow amplitude modulation J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-11 Seyed Morteza Habibi Khorasani, Mitul Luhar, Shervin Bagheri
Turbulent flows over porous lattices consisting of rectangular cuboid pores are investigated using scale-resolving direct numerical simulations. Beyond a certain threshold which is primarily determined by the wall-normal Darcy permeability, ${{\mathsf{K}}_y}$ , near-wall turbulence transitions from its canonical regime, marked by the presence of streak-like structures, to another marked by the presence
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Mixing and inter-scale energy transfer in Richtmyer–Meshkov turbulence J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Zhangbo Zhou, Juchun Ding, Wan Cheng
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Elastohydrodynamic interactions in soft hydraulic knots J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Magnus V. Paludan, Benjamin Dollet, Philippe Marmottant, Kaare H. Jensen
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Chaos via type-II intermittency in a forced globally unstable jet J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Zhijian Yang, Bo Yin, Yu Guan, Stephane Redonnet, Larry K.B. Li
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Formation and evolution of laminar thermal structures: correlation to the thermal boundary layer and effects of heating time J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Pei-Jiang Qin, Yu-Yang Hou, Ji-Dong He, Ping Wei, Shi-Di Huang
We report an experimental study of the formation and evolution of laminar thermal structures generated by a small heat source, with a focus on their correlation to the thermal boundary layer and effects of heating time $t_{heat}$ . The experiments are performed over the flux Rayleigh number ( $Ra_f$ ) range $2.1\times 10^6 \leq Ra_f \leq 3.6\times 10^{7}$ and the Prandtl number ( $Pr$ ) range $28.6
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Manipulation of a turbulent boundary layer using sinusoidal riblets J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Gioacchino Cafiero, Enrico Amico, Gaetano Iuso
We investigate experimentally the effects of micro-grooves on the development of a zero pressure gradient turbulent boundary layer at two different values of the friction Reynolds number. We consider both the well-known streamwise aligned riblets as well as wavy riblets, characterized by a sinusoidal pattern in the mean flow direction. Previous investigations by the authors showed that sinusoidal riblets
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Equatorial modons in thermal rotating shallow water model J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Noé Lahaye, Olivier Larroque, Vladimir Zeitlin
Exact steady eastward-moving vortex-dipole solutions, the equatorial modons, are constructed in the asymptotic limit of low divergence and small temperature variations in the thermal rotating shallow water (TRSW) model on the equatorial beta-plane. This regime is known to be relevant for the tropical atmosphere. The model itself is a generalization, allowing for horizontal temperature gradients, of
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Pairwise interaction of spherical particles aligned in high-frequency oscillatory flow J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 F. Kleischmann, P. Luzzatto-Fegiz, E. Meiburg, B. Vowinckel
We present a systematic simulation campaign to investigate the pairwise interaction of two mobile, monodisperse particles submerged in a viscous fluid and subjected to monochromatic oscillating flows. To this end, we employ the immersed boundary method to geometrically resolve the flow around the two particles in a non-inertial reference frame. We neglect gravity to focus on fluid–particle interactions
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Elastic particle model for coil-stretch transition of dilute polymers in an elongational flow J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Tong Gao
The phenomenon of the ‘coil-stretch’ (C-S) transition, wherein a long-chain polymer initially in a coiled state undergoes a sudden configuration change to become fully stretched under steady elongational flows, has been widely recognized. This transition can display intricate hysteresis behaviours under specific critical conditions, giving rise to unique rheological characteristics in dilute polymer
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Transonic leading-edge stall flutter: modelling, simulations and experiments J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Gaetano M.D. Currao
This work is a numerical and experimental study of a rectangular thin plate undergoing stall flutter at Mach 0.8. This constitutes one of the first studies of this kind where three-dimensionality is fully implemented in a numerical simulation including the test-section effects characterizing wind-tunnel experiments. In order to break down the fluid–structure interaction to its main driving phenomena
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Sub-filter-scale shear stress analysis in hypersonic turbulent Couette flow J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Takahiko Toki, Victor C.B. Sousa, Yongkai Chen, Carlo Scalo
Direct numerical simulations of hypersonic turbulent Couette flows are performed for top-wall Mach numbers of 6, 7 and 8, inspired by non-reactive high-enthalpy wind tunnel free-stream conditions, with the goal of analysing the physical processes driving the sub-filter-scale (SFS) stresses to inform development of large-eddy simulation techniques for hypersonic wall-bounded flows. Semi-local scaling
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From a vortex gas to a vortex crystal in instability-driven two-dimensional turbulence J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-08 Adrian van Kan, Benjamin Favier, Keith Julien, Edgar Knobloch
We study structure formation in two-dimensional turbulence driven by an external force, interpolating between linear instability forcing and random stirring, subject to nonlinear damping. Using extensive direct numerical simulations, we uncover a rich parameter space featuring four distinct branches of stationary solutions: large-scale vortices, hybrid states with embedded shielded vortices (SVs) of
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Flow–acoustic resonance mechanism in tandem deep cavities coupled with acoustic eigenmodes in turbulent shear layers J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-05 Peng Wang, Sichang Jia, Zheng He, Chuangxin He, Hyung Jin Sung, Yingzheng Liu
This study presents the interplay of flow and acoustics within tandem deep cavities, focusing on the resonance mechanism occurring between turbulent shear layers and acoustic eigenmodes. The arrangement inside the tandem deep cavities includes both close and remote configurations. A combined fully coupled and decoupled aeroacoustic simulation strategy was devised. Employing an advanced high-order spectral/hp
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Laboratory experiments of melting ice in warm salt-stratified environments J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-05 James K. Sweetman, Callum J. Shakespeare, Kial D. Stewart, Craig D. McConnochie
Melting icebergs provide nearly half of the total freshwater flux from ice shelves to the ocean, but the availability of accurate, data-constrained melting rate parametrisations limits the correct representation of this process in ocean models. Here, we investigate the melting of a vertical ice face in a warm, salt-stratified environment in a laboratory setting. Observations of the depth-dependent
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A thin-plate approximation for ocean wave interactions with an ice shelf J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-05 Luke G. Bennetts, Timothy D. Williams, Richard Porter
A variational principle is proposed to derive the governing equations for the problem of ocean wave interactions with a floating ice shelf, where the ice shelf is modelled by the full linear equations of elasticity and has an Archimedean draught. The variational principle is used to form a thin-plate approximation for the ice shelf, which includes water–ice coupling at the shelf front and extensional
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Refraction of a triple-shock configuration at planar fast–slow gas interfaces J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Enlai Zhang, Shenfei Liao, Liyong Zou, Zhigang Zhai, Jinhong Liu, Xinzhu Li
This paper characterizes the refraction of a triple-shock configuration at planar fast–slow gas interfaces. The primary objective is to reveal the wave configurations and elucidate the mechanisms governing circulation deposition and velocity perturbation on the interface caused by triple-shock refraction. The incident triple-shock configuration is generated by diffracting a planar shock around a rigid
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On the generation of near-wall dilatational motions in hypersonic turbulent boundary layers J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Ming Yu, ZiSong Zhou, SiWei Dong, XianXu Yuan, ChunXiao Xu
Dilatational motions in the shape of travelling wave packets have been identified recently to be dynamically significant in hypersonic turbulent boundary layers. The present study investigates the mechanisms of their generation and their association with the solenoidal motions, especially the well-recognized near-wall self-sustaining process of the regeneration cycle between the velocity streaks and
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Flow-induced vibrations with and without structural restoring force: convergence under the effect of path curvature J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Rémi Bourguet
When a cylinder is free to move along a transverse rectilinear path within a current, the vibrations developing with and without structural restoring force (SRF) noticeably deviate: if the elastic support is removed, their onset is delayed from a Reynolds number ( $Re$ , based on the body diameter and inflow velocity) value of approximately 20 to 30, and their peak amplitudes and frequency bandwidths
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Scaling regimes in rapidly rotating thermal convection at extreme Rayleigh numbers J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Jiaxing Song, Olga Shishkina, Xiaojue Zhu
The geostrophic turbulence in rapidly rotating thermal convection exhibits characteristics shared by many highly turbulent geophysical and astrophysical flows. In this regime, the convective length and velocity scales and heat flux are all diffusion-free, i.e. independent of the viscosity and thermal diffusivity. Our direct numerical simulations (DNS) of rotating Rayleigh–Bénard convection in domains
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Optimal wall shapes and flows for steady planar convection J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Silas Alben
We compute steady planar incompressible flows and wall shapes that maximize the rate of heat transfer ( $Nu$ ) between hot and cold walls, for a given rate of viscous dissipation by the flow ( $Pe^2$ ), with no-slip boundary conditions at the walls. In the case of no flow, we show theoretically that the optimal walls are flat and horizontal, at the minimum separation distance. We use a decoupled approximation
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Bifurcation of equilibrium positions for ellipsoidal particles in inertial shear flows between two walls J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Giuseppe Lauricella, Mohammad Moein Naderi, Jian Zhou, Ian Papautsky, Zhangli Peng
We conducted a systematic numerical investigation of spherical, prolate and oblate particles in an inertial shear flow between two parallel walls, using smoothed particle hydrodynamics (SPH). It was previously shown that above a critical Reynolds number, spherical particles experience a supercritical pitchfork bifurcation of the equilibrium position in shear flow between two parallel walls, namely
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Tailbeat perturbations improve swimming efficiency in self-propelled flapping foils J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-04 Li-Ming Chao, Laibing Jia, Liang Li
Recent studies have shown that superimposing rhythmic perturbations to oscillating tailbeats could simultaneously enhance both the thrust and efficiency (Lehn et al., Phys. Rev. Fluids, vol. 2, 2017, p. 023101; Chao et al., PNAS Nexus, vol. 3, 2024, p. 073). However, these investigations were conducted with a tethered flapping foil, overlooking the self-propulsion intrinsic to real swimming fish. Here
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Direct numerical simulations of compressible turbulent channel flows with asymmetric thermal walls J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Peng Zhang, Yubin Song, Zhenhua Xia
This paper extends the work of Tamano & Morinishi (J. Fluid Mech., vol. 548, 2006, pp. 361–373) by simulating supersonic turbulent channel flow with asymmetric thermal walls using a larger computational domain and a finer mesh. Direct numerical simulation is carried out for four cases with different thermal wall boundaries at the top wall at fixed $Ma=1.5$ , $Re=6000$ and $Pr=0.72$ , while the bottom
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Active control of flow and near-field pressure fluctuations in heated supersonic rectangular twin jets J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Mo Samimy, Karli Katterle, Ryan Leahy, Nathan Webb, Abhi Yarlagadda, Noah Hiler
Heated supersonic rectangular twin jets (SRTJ) with a total temperature ratio of 2, using nozzles of design Mach number 1.5 and aspect ratio 2, were investigated in flow regimes from overexpanded to the design condition (Mj = 1.3–1.5). This work complements our recently published work in unheated SRTJ using the same experimental facility (Samimy et al., J. Fluid Mech, vol. 959, 2023, A13). Localized
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Settling and collision of spheroidal particles with an offset mass centre in a quiescent fluid J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Xinyu Jiang, Chunxiao Xu, Lihao Zhao
Gravitational sedimentation and the collision of particles play key roles in various natural and engineering processes. In practice, particles are often non-spherical in shape with non-uniform mass distribution. In this study we investigate how the mass eccentricity influences the settling and gravitational collision of non-spherical particles in a quiescent fluid. Firstly, we theoretically analyse
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Self-similarity in over-tripped turbulent boundary-layer flows J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Zhanqi Tang, Nan Jiang
The scaling universality of structure functions is studied for artificially thickened turbulent boundary-layer flows in over-tripped impacts by using hot-wire measurement datasets. The self-similarity behaviours in the inner and outer regions are examined from the viewpoint of different flow mechanisms. In the inner region, the relative ratios between structure functions for the energy-containing range
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Buoyancy oscillations J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Bruno Voisin
The oscillations of buoyant bodies in stratified fluids are deduced from the variations of their added mass. Three configurations are considered: a body displaced from its neutral level then released; a Cartesian diver set into oscillation by a modulation of the hydrostatic pressure, then released; and a body attached to a pendulum to which an impulse is applied. The first configuration is related
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Data-driven model for Lagrangian evolution of velocity gradients in incompressible turbulent flows J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Rishita Das, Sharath S. Girimaji
Velocity gradient tensor, $A_{ij}\equiv \partial u_i/\partial x_j$ , in a turbulence flow field is modelled by separating the treatment of intermittent magnitude ( $A = \sqrt {A_{ij}A_{ij}}$ ) from that of the more universal normalised velocity gradient tensor, $b_{ij} \equiv A_{ij}/A$ . The boundedness and compactness of the $b_{ij}$ -space along with its universal dynamics allow for the development
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Scale-by-scale non-equilibrium with Kolmogorov-like scalings in non-homogeneous stationary turbulence J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 P. Beaumard, P. Bragança, C. Cuvier, K. Steiros, J.C. Vassilicos
An improved version of the non-equilibrium theory of non-homogeneous turbulence of Chen & Vassilicos (J. Fluid Mech., vol. 938, 2022, A7) predicts that an intermediate range of length scales exists where the interscale turbulence transfer rate, the two-point interspace turbulence transport rate and the two-point pressure gradient velocity correlation term in the two-point small-scale turbulent energy
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Mode coupling between two different interfaces of a gas layer subject to a shock J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-03 Chenren Chen, He Wang, Zhigang Zhai, Xisheng Luo
Shock-tube experiments and theoretical studies have been performed to highlight mode-coupling in an air–SF $_6$ –air fluid layer. Initially, the two interfaces of the layer are designed as single mode with different basic modes. It is found that as the two perturbed interfaces become closer, interface coupling induces a different mode from the basic mode on each interface. Then mode coupling further
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Instability in strongly stratified plane Couette flow with application to supercritical fluids J. Fluid Mech. (IF 3.7) Pub Date : 2024-04-02 B. Bugeat, P.C. Boldini, A.M. Hasan, R. Pecnik