Morphing Blades Can Be More Efficient than Rigid Blades

In wind turbine operation, airflow separation causes turbulence, which diminishes blade efficiency. It is therefore desirable to limit or eliminate flow separation. Many passive or active separation control mechanisms have been proposed to reduce separation. Active control systems sense the wind velocity or rotational speed, and modify blade aerodynamic configurations accordingly. Some propose employing suction within the boundary layer. Others suggest particle blow-through leading edge slots and use of trailing edge flaps. Passive vortex generators have also been proposed. Generally, all such control schemes improve the blade performance at part-load, but they also reduce blade efficiency at or near the design load. Further, in the case of active control, they come at the cost of an added power penalty as well as design complications. The use of morphing blades, however, eliminates flow separation without design point penalties.

By Asfaw Beyene, Department of Mechanical Engineering, San Diego State University, USA

What Makes Taller Towers Attractive to Developers?

Developers are seeing their turbine costs, transportation costs and installation costs going up and the potential of their new turbines curtailed by the limitations of 80-metre towers. What will taller towers do for them?

By Peder Hansen, Executive VP, Northstar Wind Towers, USA

Generating Electric Power from High Elevation Winds in Valleys

Powerful winds blow through mountain valleys worldwide. Some of these winds originate over a large body of water, such as an ocean or a sea, and accelerate to high velocity due to the low friction of the boundary layer that exists between air and water. Many such winds blow towards coastal mountains, for example the Atlas Mountains of Northwestern Africa. Powerful winds also blow at high altitudes towards valleys in mountain ranges such as the Alps. There are many valleys at various elevations in these mountains into which coastal winds and high-altitude winds may blow and accelerate to higher velocity. It is possible to adapt existing and proven technology, such as cable suspension systems, conveyor technology and airfoils, in order to generate electrical power at higher elevations than can be achieved by wind turbines on towers.

By Harry Valentine, Technical Journalist, Canada

Considerations When Choosing Bolt Tensioning Tools

Bolt tensioning is vital to the integrity of wind turbines. As well as being extremely important for applying accurate bolt loads efficiently and safely, it is also a consideration for the builders and installers of the turbines as well as for the maintenance engineers who are required to carry out regular bolt load checks. This article will look at why accurate bolt tensioning is important, particularly for foundation bolting in the USA and Canada, and what aspects are significant when choosing the right equipment for the job.

By Roy Sheldon, Business Development Manager, Tentec Ltd, UK