New storm patterns require new wind engineering

by Julian Hunt and Horia Hangan
Tuesday, 29 October 2013 17:05 GMT

A commuter loses control of his umbrella as he braves the wind and rain while crossing London Bridge in London, United Kigdom, October 28, 2013. REUTERS/Dylan Martinez

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As global warming brings worsening storms, we need a new engineering approach to prepare

This week’s hurricane-force winds across the UK and northern Europe, the worst in a decade, have mercifully resulted in only a handful of deaths.  However, the disruption and chaos they have caused serves as a warning for the future.

Gusts of almost 100 miles per hour (around 160 kilometres per hour) lashed much of southern England and Wales, with floods warnings across much of the country.  Meanwhile, hundreds of thousands of homes suffered power cuts, while the Dungeness nuclear power station was ‘knocked out’.  On the transport side, more than 130 flights were cancelled at Heathrow alone, while, remarkably, a double decker bus ‘blew over’ in Suffolk.

While many are rightly relieved that the winds did not rival the great storm of 1987, the unfortunate truth is that we are likely to face similar hurricane-force winds with greater regularity in the future.  This is yet another consequence of climate change.

It is projected that global warming will cause the average intensity of storms to increase -- which means stronger winds.  And, also there will be a rise in rainfall rates in storm centres too.
Total rainfall will also probably grow when big storms hit land.  We know already that the frequency of heavy rain events, as well as rainfall intensity (amount of rain per unit of time), has increased.
These disturbing facts mean that we need nothing less than a new approach to wind engineering.  To this end, approximately 100 researchers from across the world gathered at Western University, Canada on October 16 to explore new frontiers of wind engineering, energy and the environment.

A key challenge is that traditional wind tunnels widely used today for science and testing applications from planes to cars, buildings and air quality applications create uni-directional, and constant speed air flows.  They simply cannot reproduce the complex space and time variation of localised wind storms that we are seeing increasing today.  Moreover, due to their size and geometry, traditional wind tunnels are also not capable of reproducing all scales of wind motions involved in wind energy and wind environment studies.

However, a breakthrough is now emerging.  The WindEEE Dome at Western University, Canada is a new 25 metre diameter wind testing chamber that attempts to address these shortcomings.  The 3 E’s stand for the applications:  wind engineering (the damaging effect of wind on structures); wind energy (the positive effect of generating power out of wind); and wind environment (the way wind interacts with the natural and built habitat from forest canopies to city microclimates).

WindEEE’s hexagonal chamber has 100 fans distributed on six walls and six more, larger fans, above the chamber.  When coupled together, these 106 fans can re-create almost any type of wind system in a three-dimensional and time dependent manner.  This is a crucial development if we are to meet the challenges posed by future storms.

For instance, by coupling the fans on the periphery and injecting air into the chamber at certain angles, one can create a twist, which, in conjunction with a negative pressure created by the fans above the chamber, generates a tornado.  Or, the reverse: injecting air from the top fans into the chamber and ejecting it radially through the fans on the periphery generates a downburst/ jet-like flow.

Both the tornadoes and the downbursts wind fields can move through the chamber at rapid speeds (2 metres a second). 

Remarkably, every fan on the periphery can be actuated at 1 Hertz (i.e. the wind speed can be varied in 1 second) making the WindEEE Dome capable of actively reproducing atmospheric turbulence.

One of the many practical applications of WindEEE is that it can help us understand more about vulnerability to turbulence of high-rise towers, and other buildings and structures, so that we can develop better design codes.  This is especially important given the number of high-rise buildings being constructed right across the world, especially in coastal areas and/or growing mega-cities.   ­

Taken overall, it is clear that storms increasing have a space and time variability, non-uniformity, and much higher level complexity of wind, than traditional engineering has catered for.  As this week’s hurricane-force winds remind us, we must therefore adopt a new engineering approach to enable our preparedness.

WindEEE is a good example of exactly what is needed to make the necessary quantum leap forward in wind research.  We must now encourage similar science and technological innovation to meet the challenges posed by storms of the future.

Lord Hunt is Visiting Professor at Delft University and former Director-General of the UK Met Office. 

Professor Horia Hangan is Director of the WindEEE Research Institute at Western University Canada.