The Blue Whirl

This intriguing title describes a very pretty phenomenon, published in a paper for the PNAS (Proceedings of the National Academy of Sciences of United States of America) on 4th August 2016 by a team of scientists from the A. James Clark school of engineering, University of Maryland. It is an unprecedented form of a fire whirl, the ‘blue whirl‘, which develops from a pool fire and can be thought of as a small-scale tornado. The science behind it is pretty awesome, as well as the potential implications: from enhanced research into fluid dynamics and specifically stable vortices, to reduced CO2 emissions and improved efficiency of cleaning up oil spills on ocean surface.

You may have seen large scale natural fire whirls in action, destroying life and surroundings with their intensity and turbulence, propelled by strong winds. The blue whirl phenomenon evolves from this type of fire, with key differences of stability, a smaller size, and obviously the colour. While an orange flame in the fire whirl signifies the presence of radiating soot particles from incomplete combustion (i.e. the amount of oxygen required for all the fuel to react fully [combust] is not enough), the blueness of a flame is down to complete burning of all the fuel (I.e. There is enough oxygen in the reaction). The rate of heating is also faster and therefore more efficient.


In light of this, it has been proposed that the science behind these phenomena could be harnessed into improved methods of cleaning up oil spills. Currently, oil spills can be cleaned up with inefficient, ordinary burning of the fuel which releases an ugly amount of CO2. You’d be forgiven to question whether using this technique is worth the clean up at all, in a world where increasing emissions are pushing us off the edge of safety. But very few things tried on e.g.the BP oil spill actually worked. The experiments in Xiao’s publication were appropriately conducted on a water – fuel surface boundary, and found that whirls also pulled fuel into the lower pressure centre, making for a credible result. More large-scale experiments are needed to make this idea become reality.

This is good news for fluids dynamics research, too. There are analogies between the dynamics of the blue whirl and vortex breakdown with two modes: spiral and bubble modes. Before evolution into the blue whirl, the fire whirl can be compared to the spiral mode. Then, after swiftly evolving into the tornadoesque blue whirl, it lives for approx. 2 seconds and can be compared to the bubble mode – something not previously seen in nature to be caused by combustion (as far as the paper’s authors’ knowledge goes). So that is pretty cool. There is a nice description of all this in the short paper, so do have a read about the details if you are interested!

Here is a neat little video from the experiment: http://movie-usa.glencoesoftware.com/video/10.1073/pnas.1605860113/video-1

That’s all I really have to say, just thought I’d share this cool discovery with you all. Thanks for reading 🙂

More reading: http://www.pnas.org/content/early/2016/08/03/1605860113

http://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/resources/in-situ-burn-emissions-comparisons.html

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