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Investigation of blade tip modifications for acoustic noise reduction and rotor performance improvement

Objective

The project will test several shapes of tip using a 16 m diameter horizontal axis test wind turbine.

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 nine 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.
Medium- and large-scale wind turbines can be built more economically if it is possible to realize a lightweight design for each component. Weight reduction, however, mostly entails higher tip speeds of the blades what goes hand in hand with a higher level of aerodynamically generated noise. Bearing the acceptance of wind turbines by the public in mind, it is mandatory to avoid noise as far as possible. Whereas the structural noise generated by components like gear-boxes, generators etc... can be reduced by well known standard procedures, the aerodynamic noise, especially the one emanating from the blade tip region, has to undergo further investigation. In Europe several countries are adressing this problem so that it makes sense to undertake a joint effort, in order to avoid duplicated research. The results expected from this experimental approach should be the quantification of the tip noise as compared to other noise sources, the influence of different tip shapes on this noise and proposals for 'quiet' tips with good performance characteristics and proposals for further investigations with respect to the numerical simulation of the problem.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSITAET STUTTGART
Address
Pfaffenwaldring 27
70569 Stuttgart
Germany

Participants (3)

ENERGY RESEARCH CENTRE OF THE NETHERLANDS
Netherlands
Address
Westerduinweg 3
Petten
GERMAN AEROSPACE CENTRE
Germany
Address
Pfaffenwaldring 38-40
70569 Stuttgart
STICHTING NATIONAAL LUCHT- EN RUIMTEVAARTLABORATORIUM
Netherlands
Address
Anthony Fokkerweg 2
1006 Amsterdam