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Controlling vortex breakdown in swirling pipe flow

David Dennis (University of Liverpool)

A vortex breakdown occurs as fluid flows from a rotating pipe into a stationary pipe at a constant rate. The decaying swirl creates an adverse pressure gradient on the pipe axis, which reverses the flow and forms a recirculation "bubble". The bubble's size is controlled by the speed of rotation.

Droplet splashing on super-hydrophobic substrate (experiment or simulation?)

Kensuke Yokoi (Cardiff University)

A numerical simulation of droplet splashing on a super-hydrophobic substrate. The numerical method is based on CLSVOF, VSIAM3, CIP-CSL scheme, density-scaled balanced CSF model.

Acoustic eruption

Elijah Nazarzadeh (University of Glasgow)

'This video shows the transfer of mechanical energy and radiative pressure from Surface Acoustic Waves (SAWs) traveling along a solid surface into a droplet of water, dropped in the propagation path of SAWs, at 100k fps acquisition (slowed down 500 and 1500 times). The behaviour resembles an eruption and is used in medicine nebulisers.'

Bead formation on a viscoelastic drop’s tail

Haonan Xu (University of Liverpool)

Formation of a “beads on the tail” of a viscoelastic droplet as it moves on an inclined superhydrophobic surface. The interaction of the surface features and the viscoelasticity of the drop results in a significant slowing of the drop – in comparison with an equivalent-viscosity Newtonian drop – and an instability on this fluid tail gives rise to the bead-like structure.

Demonstration of Flowave

Clive Greated (University of Edinburgh)

‘Demonstration of the capabilities of Flowave. The principles of three-dimensional wave generation on which it is based were researched back in the early 80's by Bryden and Greated (J. Phys. D: Appl. Phys. 17, 1984).’

Interfacial waves in the two-layer rotating annulus

Paul Williams (University of Reading)

Two immiscible layers represent the stratified mid-latitude atmosphere, and internal interfacial waves develop and interact nonlinearly. A wide range of wave behaviours are observed: for example, the left-hand image shows two packets of spontaneously emitted inertia-gravity waves in the troughs of a large-scale baroclinic wave, while the right-hand image shows a rotationally modified Kelvin-Helmholtz wave generated from shear instability at sub-critical Richardson number. An optically active liquid generates different colours according to interface height.

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Petal-like fluid-driven fracture patterns

Niall O’Keeffe (University of Cambridge)

‘A fluid-driven fracture propagates radially in a transparent hydrogel. The fracture surface, post experiment, consists of beautiful fractal patterns called step-lines. These are small changes in height along the surface of the gel, which follow a logarithmic spiral shape.’

Jetting of droplet induced by ZnO-Si surface acoustic waves

Richard Fu (Northumbria University)

'This is a high speed video showing jetting behaviour of a 20μL water droplet induced by ZnO surface acoustic waves (from left side). The jetting is induced by sub-nanometre amplitudes of surface acoustic waves interacting with water droplet, causing the droplet jetting along Rayleigh angle. However, due to a combination of acoustic pressure, internal flow, gravity force, surface tension and capillary, the droplet has been deformed significantly before fully jetted from substrates. '

(Accidental) double-diffusive instability

Megan Davies Wykes (University of Cambridge)

‘Heat from lamps above the experiment is absorbed by dyed, salty fluid, heating it up and making it less dense. This warm fluid rises, but the heat diffuses away, leaving dense, salty fluid in narrow vertical plumes.’

Wake partita

Lian Gan (Durham University)

This raw video shows wake pattern behind an oscillating cylinder. The forcing amplitude keeps constant; the frequency linearly ramps down. It is part of a systematic study where ramping up and down at various rates. Compared to the fixed frequency cases, ramping results in wake mode transition, skipping and hysteresis.

Spatio-temporal feathering in elastic channels

Callum Cuttle (University of Manchester)

‘Composite binary images showing the spatio-temporal patterns formed when air displaces oil in a Hele-Shaw channel with an elastic upper boundary. By manipulating the initial level of collapse of the upper boundary, as well as the flow rate, we may observe a range of patterns, some reminiscent of feathers.’

Forces in a photoelastic avalanche

Amalia Thomas (University of Cambridge)

‘Photoelastic discs are rolled down a narrow, inclined chute. The forces exerted when discs interact can be inferred from the intensity of the light they transmit. This information can be used to investigate how stresses are distributed within avalanches.’

Simulated sperm swimming in synchrony

Simon Schöller (Imperial College, London)

A computer-generated image of model sperm cells suspended in a Stokesian fluid, including the fluid velocity field. All sperm cells swim in the same plane and interact hydrodynamically, leading to visible cluster formation and locally enhanced flows.

Wrinkly impact

Maxime Inizan, Finn Box, Alfonso Castrejon-Pita & Dominic Vella (University of Oxford)

‘When a solid sphere hits an elastic sheet floating on the surface of water, wrinkles form and a capillary-like ripple propagates. The ripple propagates and the wrinkles grow with time — all due to an interplay between the elasticity of the sheet and the inertia of the fluid.’

The effect of stratification on Kelvin-Helmholtz instability

Chris Howland (University of Cambridge)

This image is a composite of five vorticity time series from simulations of stratified shear layers with increasing stratification. Each pixel column corresponds to a single time step from each simulation.

Particle flow instability

Steven Wang & Ben Xu (Northumbria University)

Visualization of the trapping of finite Stokes number particles in a laminar flow. Three particles (in this case, LED capsules) encounter a flow instability in a chaotic flow region and eventually settle into a Kolmogorov-Arnold-Moser (KAM) tube where they move in helical orbits.

Elastic deformation revealed by colours

Jian Guan (University of Oxford)

Fingering patterns form when air is injected into dyed glycerol in a Hele-Shaw cell with a soft upper boundary. As a result, the soft layer deforms. The change in the colour intensity of the dyed fluid reveals both global and local deformations of the soft layer.

‘Halo’ vortex ring lifts dandelion seeds

Cathal Cummins, Madeleine Seale, Enrico Mastropaolo, Naomi Nakayama & Ignazio Maria Viola (University of Edinburgh)

(Left) A dandelion seed in a wind tunnel, with added clouds for effect. (Right) The same dandelion with the flow around it visualised using a laser sheet, showing the formation of a drag-enhancing vortex unlike any other observed before in nature, which we term a 'halo' vortex.

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Induced Faraday instability by two-frequency forcing

Naresh Sampara (University of Nottingham)

As a liquid bath is perturbed, Faraday waves appear on the surface. Regular square patterns are observed for single-frequency forcing and the wavelength depends on the liquid properties and exciting frequency. The regular pattern becomes more complex by adding a second frequency component into the forcing signal.

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Liquid crystal seagull

Nikita Solodkov (University of Leeds)

‘"We should show life neither as it is, nor as it should be, but as we see it in our dreams" (The Seagull, by Anton Chekhov). Liquid crystal droplets in water, (accidentally) forming a pattern resembling a seagull's landing, viewed through a cross-polarising microscope.’

The hydrodynamics of plesiosaurs

Luke Muscutt (University of Southampton)

‘A combination of data from simulations and experiments on tandem flapping flippers.’

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Kármán vortex street in the wake of an oscillating circular cylinder in laminar flow conditions

Elvin Hii (BMT UK 2 Limited)

Flow visualization for a circular cylinder section in laminar flow conditions within a wind tunnel.

Storm in a glass

Jason Stafford (Imperial College, London)

A column is formed in a rotating glass of water as fluorescent green dye is introduced. At low Rossby number, the Coriolis force dominates, controlling the dye motion. This unfiltered UV-illuminated image shows spiral filaments, mirroring the structure of a large-scale natural storm, also governed by the same invisible force.

Shock-waves over a flexible surface in a supersonic wind tunnel

Michela Gramola (Imperial College, London)

'The images show the evolution of the structure of a shock-wave formed on a flexible aluminium plate as the supersonic flow interacts with the changing geometry of the deforming surface. Each pop art-inspired image is a composite of eight individual frames acquired using Schlieren photography in a supersonic wind tunnel.'

Finding Nessie: the structure and origin of confined Holmboe waves

Adrien Lefauve (University of Cambridge)

This video relates our journey to look for order in the chaos of stratified turbulent flows. We tell the story of how we found three-dimensional coherent structures using cutting-edge experiments, and how we are just beginning to understand their origin using a modern stability analysis.