Journal of Fluid Mechanics

In this study, we present the discovery of an inverse-square force between evaporating sessile droplets. We find that one evaporating sessile droplet exerts a driving force on another, with the magnitude of the force decaying inversely proportional to the square of distance between their centres. The inverse-distance decay of the vapour concentration generated by the source droplet is a key ingre…

Direct numerical simulations (DNS) are used to study the evolution of hairpin vortices to understand the late-stage turbulent breakdown of vortex rings. Several hairpin initial configurations with Reynolds number italic Re equals 1500 <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http…

Nonlinear hydrodynamic effects influence the power capture of resonant wave energy converters (WECs), particularly within the frequency band where these devices are designed to operate. In this study, wave flume experiments are conducted on a semi-immersed spherical model with prescribed heave motions, emulating the response to an incident broad-banded wave group. Several body motion amplitudes (…

We investigate the influence of insoluble surfactants on the spatio-temporal evolution of breaking waves, focusing on both regular and spilling regimes. Three-dimensional direct numerical simulations are conducted using an interface-tracking/level-set method that incorporates surfactant-induced Marangoni stresses. The simulations reveal that surfactant gradients, through Marangoni stresses, marke…

We investigate interfacial dynamics and multiscale energy transfer in immiscible Rayleigh–Taylor turbulence using numerical simulations with varying surface-tension coefficients sigma <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cam…

Advective dispersion of neutral solutes in flow is pertinent to the design of a host of physical systems, including microfluidic devices and chemical separation systems. The cross-sectional shapes of the channels within these devices are often complex and may vary (in shape or area) in the flow direction. However, previous analyses of Taylor–Aris dispersion in channels of varying geometry typical…

Leveraging experimental measurements in rough-wall turbulent boundary layers that provided the spatial distribution and statistics of uniform momentum zones (UMZs), we previously introduced a stochastic model to generate two-dimensional modal velocity fields representative of the roughness sublayer and logarithmic region (Ehsani et al. 2024 a J. Fluid Mech. , vol. 979, p. A12; J. Fluid Mech. , 20…

We investigate the free fall of a flexible plate with a concentrated central weight using numerical simulations to explore the coupling effects of structural flexibility and concentrated loading. Two-dimensional and three-dimensional (3-D) simulations, combining lattice Boltzmann and immersed boundary methods, identify four distinct falling modes: swing, stable falling, fluttering and tumbling. T…

The motion of an immersed granular material in a channel is characterised by complex interactions among the grains, between the grains and the permeating liquid, and between the grains and the channel walls. Here, we develop a reduced-order continuum model for the bulldozing of an immersed, sedimented granular material by a piston in a channel. In our continuum approach, the granular layer and th…

We use particle simulations to reveal two distinct propulsion mechanisms for a scallop-like swimmer to propel itself in granular media by reciprocally flapping its wings. Based on the discrete element method, we examine the structure, kinematics and contact forces of particles near the swimmer to quantify how jamming manifests as stagnant zones near the swimmer in a frictional granular medium, wh…

The effects of transverse gusts on free-falling plates are investigated using two-way coupled fluid–structure interaction simulations for a Galilei number ( italic Ga <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/m…

Time-resolved particle image velocimetry and hot-wire anemometry are employed to examine the spectral characteristics and frequency-dependent convection velocities of a turbulent boundary layer developing over an axisymmetric body of revolution subjected to varying pressure gradients and curvature. After a predominantly zero pressure-gradient (ZPG) cylindrical mid-body, the boundary layer contrac…

Ice melting into saline water plays a fundamental role in the dynamics near the ice–ocean interface in polar oceans. The physics of meltwater transport involves a non-trivial interplay between the thermodynamics at the interface, hydrodynamic transport in the bulk and the properties of the ambient ocean. The key control parameters are the density ratio upper R Subscript rho <mml:math xmlns:xlink=…

This paper considers the theoretical operation of a novel wall-mounted oscillating water column wave energy device designed to be resonant over a broad range of frequencies. A curved duct with a submerged opening in a vertical wall is partitioned into a number of separate narrow channels of uniform width using thin annular baffles. Each channel connects the submerged opening to its own internal f…

We consider the plane problem of unsteady flow generated on the interface of a two-layer infinite fluid by a smooth start of a horizontal circular cylinder. The problem is reduced to an integro-differential system of equations for the functions defining the normal and tangential velocity components of fluid particles on the interface and the shape of the interface. A small-time asymptotic solutio…

Shallow flows partially obstructed by arrays of rigid elements develop a lateral shear layer that controls momentum exchange, turbulence production and scalar transport. We investigate this interfacial region through a tractable two-layer theoretical framework, laboratory measurements in an unusually wide (4 m) flume and graphics processing unit-accelerated weakly compressible smoothed particle h…

This study examines the streamwise development of secondary currents (SCs) and very-large-scale motions (VLSMs) in a rough-bed open-channel flume. We used long-duration stereoscopic particle image velocimetry at six cross-sections, extending up to 300 flow depths downstream from the flume entrance, to obtain detailed velocity fields, stress distributions and spectra. SCs were initially observed w…

This study presents a quantitative analysis of the onset of self-induced thermoacoustic instabilities in a flame propagating through a channel open only at the ignition end. Direct numerical simulations are performed for a stoichiometric mixture to examine flame–acoustic interactions in two computational set-ups: (i) a conventional truncated domain that models only the channel, imposing a constan…

We investigate transient ventilation flows following variations in the heat load and ventilation rate in a building with upward mechanical displacement ventilation. In steady state, thermal plumes that rise from localised heat sources interact with the upward ventilation flow to produce a two-layer stratification. Through new laboratory experiments, we examine the transient responses to changes i…

This study investigates the impacts of blade aerodynamic design, specifically the spanwise distribution of axial force, on the wake dynamics in tandem turbine configurations. Using large-eddy simulations with actuator surface models, we analyse five tandem set-ups comprising three blade designs: a baseline (NREL-Ori), a root-loaded (NREL-Root) and a tip-loaded (NREL-Tip) variant. Two scenarios ar…