IEA ANNEX-XIV Background and Objectives

The objective of the ANNEX-XIV was defined as the coordination of full scale aerodynamic test programs on wind turbines, in order to acquire the maximum of experimental data at minimum costs.

In these full scale aerodynamic test programs local aerodynamic quantities (forces, inflow velocities, inflow angles) are measured at several radial positions along the blade. The supply of local aerodynamic data, is a major step forward in understanding the very complicated aerodynamic behaviour of a wind turbine. In conventional test programs only blade (or rotor) quantities are measured. Usually these quantities are integrated over the rotor blade(s) and they are not only influenced by aerodynamic effects, but also by mass effects. Then the local aerodynamic properties of the blade can only be derived indirectly, introducing an uncertainty.

A total of five full scale aerodynamic test programs were coordinated.

The programs were carried out by:

• Delft University of Technology, DUT Netherlands:The DUT experiments are carried out on a 2 bladed, 10 m diameter turbine. The blades are untwisted and untapered.
• Imperial College, IC and Rutherford Appleton Laboratory, RAL, United Kingdom:The IC/RAL experiments are carried out on a 3 bladed, 16.9 m diameter turbine. The blades are twisted and tapered.
• Energy Research Centre of the Netherlands ECN (Operating Agent):The ECN experiments are carried out on a 2 bladed, 27.4 m diameter turbine. The blades are twisted and tapered.
• National Renewable Energy Laboratory, NREL, USA:The NREL experiments are carried out on a 3 bladed, 10 m diameter turbine. Measurements on two types of blades have been supplied: An untwisted and untapered blade; A similar blade, without taper, but with twist.
• RISØ National Laboratory, Denmark:The RISØ experiments are carried out on a 3 bladed, 19 m diameter turbine. The blades are twisted and tapered.

The background for the project was the following: It should be realised that aerodynamic field experiments are typically very time consuming, expensive and complicated through the large volumes of data and the extensive data reduction which are required. Furthermore, each turbine configuraton that is investigated experimentally may exhibit a very different aerodynamic response characteristic. Hence, the results which are obtained from only one (very time consuming, expensive and complicated) experiment may have a limited validity.

For this reason it was considered very advantageous to cooperate in these experiments. The combination of measurement data on very different facilities will provide much more insight about the general validity of aerodynamic phenomena.

This co-operation is established in the IEA ANNEX-XIV 'Field Rotor Aerodynamics' which commenced in 1992 and was ended in 1997.