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Twist again

Research; Funding

'Twisters' are well-named. Inside a typical tornado the winds rotate in tight circles between 20m and 200m across, reaching velocities of 300km/h or more. Yet designing structures to resist tornadoes is almost impossible - because no one has managed to simulate a tornado in the laboratory and analyse its effects on model structures.

Building Research Establishment senior research engineer Gordon Breeze explains: 'All we can do is measure maximum wind speeds inside tornadoes by radar then run our wind tunnels at that speed.

'But airflow in a conventional wind tunnel is virtually linear, so the loading on the test structures is really nothing like that produced by a rotating tornado.'

Breeze's idea for a tornado tunnel is still at the back of the envelope stage, and the £1M would go into proving the basic concept. He is certain that he could produce a realistic miniature tornado in a notch in the side of a conventional wind tunnel. Extra realism could be added by tapering the notch in elevation to lend the 'circulating bubble' the funnel-shaped profile of the real thing.

Energy from the airflow in the main tunnel would maintain the tornado, and Breeze says a model structure could be introduced into the bottom of the notch. 'The real breakthrough would be to use computer-controlled air jets to nudge the mini-tornado into the main airflow, then strike the test structures in a more realistic manner.'

A small water tunnel would be the first step before moving on to a modified conventional wind tunnel. Further trials would need a 'three component laser Doppler anemometer' to measure air movements in three dimensions. 'That alone would cost the best part of £1M,' Breeze adds.

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