Earlier this year Opus Research relocated to new premises in Petone, Wellington, where it built a brand new boundary-layer wind tunnel – the only commercially owned and operated wind engineering facility in New Zealand.
The Opus Wind Tunnel is used primarily for environmental testing of wind flows around buildings and new developments. It has also been used for one-off projects such as examining the wind flow around cricket balls for swing bowlers, testing the strength of different umbrella designs and looking at snow drift around buildings at Scott Base in Antarctica.
The wind tunnel has a recirculating configuration with a 3m by 1.5m cross-section, computer-controlled instrumentation and data acquisition systems, and an extensive reference library acquired from over 40 years of analytical investigations, modelling and full-scale testing.
Common wind issues resulting from new building developments include people and amenities being blown around at street level; noise resulting from sharp edges, shape geometry and the volume of spaces wind is forced to flow through; and damage to cladding, facades and other design features. Such issues derive from building design and alterations,and can be readily identified and mitigated through testing in the Opus Wind Tunnel.
In studies of wind flows around buildings and new developments, for example, the force that pedestrians feel is proportional to the wind speed squared; so if you double the wind speed, the force increases by a factor of four. Increases in wind speed from an existing gust speed of 10m/s to 20m/s are not uncommon, with one of the biggest wind effects being an increase in gust speed from 17m/s to 35m/s.
Examples of wind tunnel investigations include the effects of strong winds around the Novotel Auckland Airport Hotel which were causing stoppages and performance problems with the building’s revolving door entry. Mitigation strategies including changes to the existing canopy and various combinations of vertical screens and fences were investigated in the wind tunnel. Short vertical screens located close to the entrance were recommended as a result of the study.
The original design of the Majestic Centre, Wellington was a tall, rectangular shape with hard edges. When it was tested in the tunnel the wind effects at ground level were extreme and unsafe for pedestrians. Opus Research and the designers played around with the shape and ended up with the round, smoother design it now is. However, wind effects around the building’s entranceway were still problematic so Opus Research designed a perforated, space-frame canopy which effectively breaks up the wind as it comes down the front of the building.
When the original design for Westpac Stadium in Wellington was put through the Opus Wind Tunnel there was too much wind loading on the roof, which meant it would have needed to be extremely strong and expensive. As a result of tunnel testing Opus Research designed an offset leading edge to the roof which drastically reduced wind loads and enabled the design and build of a lower strength/lower cost roof. They also designed the slatted metal screens on the walkway from the stadium to the train station which reduces wind impact on pedestrians.
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