A peek at the design process

Some of the mystique associated with wind turbine design is dispelled by a doctoral thesis entitled "Optimisation of wind turbine rotors" which unusually attempts a complete analysis of the design process. The study, by Norwegian academic Tor Nygaard, includes aerodynamic analysis, a structural dynamic model and a cost model.

Wind turbine design processes are mostly well-guarded commercial secrets and it is rare to come across complete descriptions of them. Nygaard's optimisation covers a wide range of variables including airfoil sections, rotational speed, rated power and blade shape.

He concludes that the optimum level for rated power is about 500 watts per square meter, although this value rises with increased wind speed. Rotor performance is not critically dependent on airfoil characteristics, although some benefits are derived if the maximum lift coefficient is higher at the root than at the tip.

A new low-lift airfoil family developed specifically for wind turbine purposes appeared to offer a modest but worthwhile saving in the cost of energy, according to Nygaard. Although difficult to assess the accuracy of his study, it gives useful insights into the design process.