Pioneering
mathematical engineers have discovered for the first time a rigid structure
which exists within the centre of turbulence, leading to hope that its chaotic
movement could be controlled in the future.
Dr Sotos Generalis
from Aston University in Birmingham and Dr Tomoaki Itano from Kansai University
in Osaka, Japan, believe their discovery of the Hairpin Vortex Solution could
revolutionise our understanding of turbulence and our ability to control it. This rigid, set structure, named after its
hairpin like shape was found within Plane Couette flow. This is a prototype of
turbulent shear flow, where turbulence is created in fluid flow between the
space of two opposite moving planar fluid boundaries, when high- and low-speed
fluids collide.
Everyone from Formula One drivers experiencing drag, through to aeroplane
passengers suffering a bumpy flight, will have experienced clear-air
turbulence, the mixing of high- and low-speed air in the atmosphere.
This newly found
turbulent state is constituted by a number of elements found in a coherent flow
structure and has been described by the research team as a "tapestry of
knotted vortices."
While structures, known as wall structures have been found on the ‘edge’ of
turbulence, an elusive middle or wake structure has never been discovered,
until now.
Dr Generalis
believes that finding a regimented structure within the very heart of Couette
flow could prove invaluable to controlling turbulence and the effects of
turbulence between two moving boundaries, in the future. This could include
working machinery parts, medical treatment involving blood flow, and turbulence
in air, sea and road travel.
“Ten years ago
scientists believed turbulence was in a ‘world’ of its own, until we began to
find ‘wall structures’ on its side. We believed a middle or wake structure
might exist, and now we can prove there is regimented structure at the very
centre of turbulence. This new discovery paves the way for the ‘marriage’
between wake and wall structures in shear flow turbulence and provides a unique
picture of the Couette flow turbulent eddies only observed but never understood
before.
The team’s findings
of this missing central link have been published in Physical Review Letters and
come after nearly five years of research, created by thousands of computer
generated shear flow models. The result was obtained by replicating the
exposure of two opposite plates to hot and cold conditions, moving from a
static to dynamic position. The research team are now aiming to find if similar
structures exist within other cases of turbulent fluid flow.
“The hairpins
expose an all new ‘view’ of the transition to turbulence and it is our aim to
‘unify’ this idea discovered in Couette flow, into other areas of shear flow in
general,” added Dr Generalis.
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