Photo Entries

Below are the finalist photo entries of the fifth UK Fluids Network photo and video competition with theme 'Instability' - click here to vote for the finalist videos.

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N.B. Only one vote is accepted in each category.

Janus microparticles formed by spinodal instability within microfluidically-generated droplets
Gentle evaporation of dichloromethane from monodispersed droplets composed of a mixture of poly(vinyl acetate) and polystyrene dissolved in dichloromethane caused thermodynamic instability and phase separation into hydrophobic polystyrene and hydrophilic poly(vinyl acetate) halves. Poly(vinyl acetate) regions are more porous due to higher instability of this polymer in dichloromethane.
Particle flow instability
Visualization of the trapping of finite Stokes number particles in a laminar flow. Three particles 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. Particles used in this case are few LED capsules.
Haze flow
Wildfires associated with slash and burn agriculture on peatlands have a massive impact on climate change and regional transboundary air pollution. This August, my research group conducted the world's first field-scale peatland fire experiments. The experimental field campaign aimed to understand the behaviour of peat fires. One of the most important objectives is to understand the gas emission, which can cause deadly haze crisis. In this photo, after surface soil burning to black, there is still smouldering underground, giving haze emission continuously. This kind of emission is different to the smoke emission from flaming fires, which can go up to atmosphere. The gas emission from peat fire has low buoyancy, which makes it spread close to land and transport to cities. The state of the gas transportation in this photo shows the instability of the gas flow.
Induced Faraday instability by two-frequency forcing
As a liquid bath is perturbed, at a particular acceleration a standing wave, called Faraday waves, will appear on the whole surface of the bath. 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. A slight presence of the second frequency does not affect the instability as triggered by the first. However when both acceleration are large, the more complex quasi patterns are produced. (Liquid bath: Silicone oil 20 Cst, light with pink and white diffuse, Nikon camera with macro lens.)
Impact of a water droplet on a suspended metallic mesh
The sequence in false colours shows the impact of a water droplet onto a suspended stainless steel mesh. After the impact, the droplet penetrates completely under the porous mesh, generating a spray cone and breaking up in a higher number of smaller droplets.
The many faces of the Rayleigh-Taylor instability
Multi-physics system consisting of a heavy fluid sinking into lighter fluid, externally controlled using electric fields. Central three images (not enhanced, left to right): vorticity field, fluid phases, underlying computational grid. Side images: dedicated watercolour paintings of the instability by illustrator and collaborator Anca Pora (https://ancapora.com/).
Dye flow visualisation of vortex shedding in a synthetic jet
Dye visualisation of the formation of a synthetic jet in water (top left to bottom right), whose non-dimensional stroke length exceeds the circulation limit of the primary vortex. Consequently, excess circulation is shed resulting in an unstable shear column, followed by the roll-up of secondary (and tertiary) vortices. Composite image; not enhanced.
Folding of a particle-stabilized fluid-fluid interface
A glycerol-in-oil emulsion has decomposed into a single coalesced glycerol drop (right), but the incompressible particle-laden interface reacts by buckling into ripples and droplets. The image was produced via fluorescence confocal microscopy, with nanoparticles shown as green and glycerol as red; the optical transmission channel is overlaid in blue.
Particle induced instability at ice-water interface
When freezing unidirectionally at low velocity, particles pile up at the ice-water interface. After sufficient accumulation of the particles, it destabilises the interface and bulk ice differentiates into smaller ice-fingers. The image was coloured with the orientation of particles, the kaleidoscopic pattern suggests the particles forms clusters with different orientations.
Kármán vortex street in the wake of an oscillating circular cylinder in laminar flow conditions
Flow visualization for a circular cylinder section in laminar flow conditions within a wind tunnel. Non-composite photograph, standard touch-up with (contrast, highlights, shadows etc.)