How do Bubbles Freeze?

Freezing bubbles are not only beautiful, but also demonstrate incredibly complex physics. Here, Professor Jonathan Boreyko explains how bubbles freeze with examples of slow motion videos filmed in his laboratory at Virginia Tech.

This video is part of a collaboration between FYFD and the Journal of Fluid Mechanics featuring a series of interviews with researchers from the APS DFD 2017 conference.

Sponsored by FYFD, the Journal of Fluid Mechanics, and the UK Fluids Network. Produced by Tom Crawford and Nicole Sharp with assistance from A.J. Fillo.

Using maths to clean-up our oceans

Video of my ‘Teddy Talk’ at the 2019 St Edmund Hall open day.

Rivers are the major source of pollution in the oceans and if we are to clean them up, we first need to know where the majority of the pollution is concentrated. By creating a mathematical model for river outflows – verified by laboratory experiments and fieldwork – the goal is to be able to predict which areas are most susceptible to pollution from rivers and thus coordinate clean-up operations as effectively as possible.

Brazil Nut Effect in Avalanches and Cereal

The brazil nut effect describes the movement of large particles to the top of a container after shaking. The same effect also occurs in avalanches where large blocks of ice and rocks are seen on the surface, and in a box of cereal where the large pieces migrate to the top and the smaller dusty particles remain at the bottom. In this video, Nathalie Vriend and Jonny Tsang from the University of Cambridge explain how the granular fingering instability causes granular convection and particle segregation, with examples of experiments and numerical simulations from their research.

 

This video is part of a collaboration between FYFD and the Journal of Fluid Mechanics featuring a series of interviews with researchers from the APS DFD 2017 conference. Sponsored by FYFD, the Journal of Fluid Mechanics, and the UK Fluids Network. Produced by Tom Crawford and Nicole Sharp with assistance from A.J. Fillo.

On Zientzia Video Competition

My video ‘how plesiosaurs ruled the ocean with their flippers’ has been shortlisted for a prize in the On Zientzia science video competition. You can vote for my entry by clicking here and rating the video out of 5 stars. 

“The aim of the competition is to promote the production and dissemination of short, original videos that foment positive and progress values of science and technology, and that can be used by any kind of public for consultation purposes. The subject is totally free and can deal with one’s own or other people’s research, red-hot issues in society or the scientific community, personal scientific and technical passions, basic science concepts, scientific milestones, historical figures and science of the future or the past.”

Martin Fourcade: the Science behind the Olympic Biathlon Skiing Champion

Five-time Olympic Biathlon Skiing Champion Martin Fourcade enlisted the help of two scientists – Caroline Cohen and Christophe Clanet at Ecole Polytechnique – to help to decide the best type of wax to use on his skis in the 2018 PyeongChang Winter Olympics. Here’s how they did it…

Sponsored by FYFD, the Journal of Fluid Mechanics, and the UK Fluids Network. Produced by Tom Crawford and Nicole Sharp with assistance from A.J. Fillo.

Vortex Ring Collisions and Transition to Turbulence

Vortex ring collisions are incredibly beautiful and also incredibly complex. Ryan McKeown of Harvard University explains his amazing experiments visualising colliding vortex rings and their transition to turbulence.

Every year the Gallery of Fluid Motion video contest features the newest and most beautiful research in fluid dynamics. Watch all of the Gallery of Fluid Motion videos here: http://gfm.aps.org.

This video is part of a collaboration between FYFD and the Journal of Fluid Mechanics featuring a series of interviews with researchers from the APS DFD 2017 conference. Sponsored by FYFD, the Journal of Fluid Mechanics, and the UK Fluids Network. Produced by Tom Crawford and Nicole Sharp with assistance from A.J. Fillo.

Featuring:

R. McKeown et al. “The emergence of small scales in vortex ring collisions” https://doi.org/10.1103/APS.DFD.2017….

Physical Review Fluids publication: https://doi.org/10.1103/PhysRevFluids…

Air Pollution Risk of Cooking Oil Droplets

Cooking oil in a frying pan can be dangerous when the ‘explosive’ droplets touch your skin, but new research shows that they also increase the risk of indoor air pollution if not properly ventilated. Interview with Jeremy Marston and Tadd Truscott at Texas Tech University and Utah State University.

Every year the Gallery of Fluid Motion video contest features the newest and most beautiful research in fluid dynamics. Watch all of the Gallery of Fluid Motion videos here: http://gfm.aps.org.

This video is part of a collaboration between FYFD and the Journal of Fluid Mechanics featuring a series of interviews with researchers from the APS DFD 2017 conference. Sponsored by FYFD, the Journal of Fluid Mechanics, and the UK Fluids Network. Produced by Tom Crawford and Nicole Sharp with assistance from A.J. Fillo.

JFM China Symposia: Hangzhou

I’m in China this week documenting the JFM Symposia ‘from fundamentals to applied fluid mechanics’ in the three cities of Shenzhen, Hangzhou and Beijing. Check out the CUP website for daily blog entries as well as some of my favourite video highlights from the scientific talks in Hangzhou below.

Detlef Lohse describes how a good scientist must be patient like a good bird-watcher as demonstrated by his experiments with exploding ice droplets

Hang Ding discusses falling droplets and shows a video of one hitting a mosquito

Quan Zhou presents some amazing visuals of Rayleigh-Taylor turbulence 

Let the Floodgates Open

If you’ve been following so far, we know why it’s useful to know where river water goes when it enters the ocean, why we can build a model of the situation in the lab, what the most important variables in the problem are and what the experimental setup looks like. I suppose you’re probably itching to know what actually happens when we open the floodgates and release the freshwater from the model river into the spinning saltwater tank that is our ocean. In which case, let me point you in the direction of the video below.

It probably doesn’t make much sense without some added explanation so here goes… This is a false colour image of an experiment viewed from above. The freshwater from the river is dyed red with food colouring which means that we can convert the colour intensity into a depth measurement. The more intense the red food colouring, i.e. the more of it there is, the deeper the current must be. The scale starts with black to represent no current (as is the case for the saltwater ocean), then increases with the current depth through red, yellow, green and finally blue for the deepest parts of the current.

If you look at the very beginning of the video you will see that as the river water is released from the source it travels forwards and then is immediately forced to turn to the right. This is due to the Coriolis force arising from the rotating tank (see article 3). As it turns back on itself it eventually collides with the tank wall where it then propagates as an anticlockwise boundary current. The anticlockwise direction is set by the direction of the rotation of the tank (also anticlockwise). The boundary current continues to travel around the edge of the tank, eventually filling the whole perimeter and returning back to the source by the end of the experiment.

As well as the propagating current, a second persistent feature can also be seen in the video: the outflow vortex. This is the large whirlpool-like feature that forms next to the source of freshwater. As the initial current turns to the right and back on itself to collide with the tank wall, the flow divides. One part moves anticlockwise and forms the boundary current that moves around the tank edge, whilst the other part continues in a clockwise direction and re-joins the initial jet of freshwater from the source. The result of this is to form a whirlpool next to the source which grows in size as the experiment progresses. Both features are labelled in the image below so that you can recognise them in the video.

Screen Shot 2017-11-15 at 10.45.52.png

Now that we’ve identified the two main features of the flow – the boundary current and the outflow vortex – the next step is to try to understand them in more detail. This is exactly what the first two sections of my thesis are about, beginning with the boundary current. For example, we might want to know how fast the current moves around the tank, how its depth changes as it does so and whether or not it has a constant width. For the outflow vortex, we are interested in similar properties, such as how deep the vortex is at its centre, what shape it forms at the surface and how it grows in size during an experiment. By looking at the experimental video you can begin to get a grasp on some of these questions, but to really understand them in detail you need two key ingredients: measurements and a mathematical theory.

In my thesis, I begin by discussing the mathematical models used to describe the flow and then compare this theory with the data collected from the experiments, with the hope that they will agree. The theory can only be correct if the measurements support it – which is pretty much my thesis in a nutshell. Do the predictions from the mathematical equations agree with the observations in the experiments? If we’re going to compare the two, we’d better start by forming some equations, which brings me nicely onto the next topic…

 

You can read the rest of the articles explaining my PhD thesis here.

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