Exploitable results
The project has demonstrated that significant noise reductions can be achieved by modifications to the blade tips of wind turbine blades. Improving the noise characteristics of wind turbines will help secure the approval, during the planning process, of those directly affected by wind energy developments.
A widespread literature review of aerodynamic noise was undertaken followed by simulations. This information was used to design and manufacture 9 state-of-the-art blade tips, including a reference blade tip, each varying in plan and edge configuration. These were then fitted to an experimental wind turbine. Since 2 different blade tips could be mounted on the turbine blades in one experiment, it was possible to examine and compare 2 blade tips under exactly the same wind conditions. Both near- and far-field measuring techniques were used to make these direct comparisons. Wind tunnel experiments were also conducted to confirm results from the field tests.
Results from the simulation experiments confirmed theoretical estimates that the maximum noise reduction from tip modifications was limited to 5 dB, an important noise threshold. However, experimental investigation of the 9 blade tips led to an unexpected result. The noise level of the reference blade tip was 2-3 dB smaller than the dedicated designs of blade tip. Bevelling the trailing edge gave an additional overall noise reduction of nearly 1 dB, with a reduction of 1-5 dB in the frequency range 2-5 kHz. These results were also confirmed by non-rotating wind tunnel experiments. The results from this project are extremely important for they show that it is not only theoretically possible to reduce noise by 3 dB with proper blade tip design, but that it is likely that under current regulations it is feasible to install twice the wind turbine capacity on the same land area.
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