Understanding cyclones better: research

 The eye of a cyclone. Photo by EMA, Attorney-General's Department.

The eye of a cyclone. Photo by EMA, Attorney-General's Department.

New research on turbulence from The Australian National University will enhance wind energy technologies and improve predictions on cyclone behaviour.

The findings, published today by Dr Hua Xia, David Byrne and Professor Michael Shats from ANU, with colleague Professor Gregory Falkovich from the Weizmann Institute of Science in Israel, have the potential to address one of the most important questions in meteorology: how to better predict the behaviour of tropical cyclones.

‘Tropical cyclones, which can be up to 1000 kilometres in diameter, are dampened by their drag over ocean and land,’ said Professor Shats. ‘This drag was expected to increase with wind speed. However, meteorologists find quite the opposite ’ the stronger the cyclone the lower the drag.

?Our research shows that as a vortex, or a whirling masse of fluid, moves, it modifies turbulence beneath it. This reduces its drag as well as changes the turbulence so that it feeds a large vortex rather than dampening it.

‘In other words, cyclones lose less momentum and energy the stronger they get,’ he said.

Professor Shats said that laboratory experiments revealed that large vortices have the capacity to transform a three-dimensional turbulent flow into a two-dimensional flow.

‘Three-dimensional turbulence ’ in which vortices stretch vertically - are observed universally, and can be seen in things like water flowing through a pipe,? said Professor Shats.

‘In comparison two-dimensional turbulent flows ’ in which vortices are flat as pancakes - are much harder to observe. However our laboratory experiments have revealed that sometimes turbulence behaves as if it were two-dimensional, even in situations when it is considered impossible,? he said.

The researchers said the new discovery will also increase our understanding of atmospheric turbulence and enhance wind prediction at heights of 60 to 100 metres - a height range important for wind energy.

‘A height range of 60 to 100 metres corresponds to the heights of modern powerful wind turbines,’ said Professor Shats. ’Although wind energy has the advantage of being clean and green, it also creates a level of uncertainty for power grids because of a high variability which is very hard to predict.

‘Therefore understanding the structure of winds at these heights will help develop realistic models for future power grids dominated by renewable energy sources,’ he said.

For interviews: Professor Michael Shats - 02 6125 0038 / 0405 146 173

For media assistance: James Giggacher, ANU Media - 02 6125 7988 / 0416 249 241

 
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