ICE London Civil Engineering Awards 2013
Sky Wind Turbine
Structural & Services Engineer and Architect: Arup Associates
Client: British Sky Broadcasting (BSkyB)
Steel Fabricator: William Hare Limited
Principal Contractor: MITIE
Cost Consultant: Davis Langdon
All images © Arup Associates
Sky’s new wind turbine represents a UK first agreement negotiated with Heathrow approach control and NATS (National Air Traffic Control Services) to use radar blanking for wind turbines in close proximity to runways. At 57m high, it is also a prominent demonstrator for renewable energy in London and puts renewable infrastructure firmly onto the main-stream architectural stage.
In support of Sky’s carbon neutral status, Arup Associates designed Sky studios to be one of the most energy efficient broadcast facilities in the world. However, these buildings are by nature energy intensive, so meeting the London target for 20% on-site renewable energy generation needed a significant renewable energy infrastructure investment. The wind turbine is part of a mixed-basket of onsite renewables, and provides an estimated annual output of 133MWhr/ year, enough to power the lights of Sky studios, achieving a carbon payback of under 2.5 years on its embodied carbon.
The spiralling and tapering tower effectively mitigates the risk of resonant excitation from wind vortices through innovative passive design, without expensive damping systems. The frequency of wind vortices created by wind passing around an object depends in part on its shape. For a constant cross-section, these vortices will form at similar frequencies up the tower creating a risk of resonant excitation if the natural frequency of the tower is similar to the frequency of the vortices. Sky’s tower constantly changes shape up its height, changing the frequency of the vortex shedding. As the tower twists, the direction of the wind relative to the edges of the tower also changes, so the direction and location of the vortices change. The perforated cladding also helps to mitigate excitation from wind, by allowing some wind to pass directly through the tower.
The design thus had to be bespoke to the turbine rotational behaviour and was developed in collaboration with the manufacturer. Using state-of-the-art aero-elastic simulation and fatigue analysis produced an optimized design for Sky and also for any ‘Class III’ application of a Northwind 100kW turbine.
Architecturally the twist of the tower expresses the rotational dynamics of the turbine and allows the tower to grow seamlessly out of the plant compound below. The cladding connects the tower in place to the adjacent studio complex.
The fabrication and erection of the tower required a high degree of accuracy and stringent quality control to avoid any sources of premature fatigue cracking in the structure. The structure was fabricated in jigs, which were then for the site assembly phase. Cladding was also optimised through pressure tests to minimise stiffening.
The tower was assembled and clad at ground level to minimise working at height and then lifted in three sections in a single day. A Specialist erection team then added the nacelle and blades the following day. This strategy also minimised the amount of lifting adjacent to Sky’s studios which are in use.
The turbine’s power output is currently exceeding expectations, delivering significant energy at relatively low wind-speeds.
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