Wind turbine noise measurements in controlled conditions

To validate and reduce the uncertainty associated with noise prediction models for wind turbines, there is a need for detailed noise measurements on wind turbines in controlled conditions. However, high-quality wind tunnel campaigns on horizontal axis wind turbine models are scarce due to the large wind tunnel size needed and consequently high associated costs. To serve this purpose, an experiment using the 4.5-m diameter Mexico turbine was set up in the large low-speed facility of the DNW wind tunnel. An overview of the experiments is given including a selection of results. Both far field microphone as well as microphone array measurements have been performed together with unsteady force measurements on five instrumented blade sections. This allows a unique insight into the relation between acoustics and the underlying aerodynamics. Overall noise characteristics of the turbine have been determined for a variety of operational conditions by varying tip speed ratio and blade pitch angles. Scaling of the noise is studied by comparing similar combinations of tip speed ratio and pitch angle for different tip speeds. The effect of blade soiling on the noise is evaluated using roughness strips, as well as the influence of yawed or misaligned inflow on the rotor noise. A comparison of calculations using a BPM model is given indicating for which operational conditions this model suffices and for which parts the noise prediction can be improved. In summary, after years of preparation, ECN and partners have performed very successful aeroacoustic experiments in the largest wind tunnel in Europe. The comprehensive high-quality database that has been obtained will be used in the international Mexnext consortium to further improve wind turbine acoustic modeling.