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Investigation of serrated trailing edge noise

Objective



Objectives

The objective of the project is the reduction of the noise emitted by a horizontal axis wind turbine by the application of serrated trailing edges. The most dominant aeroacoustic noise sources, the trailing-edge noise and the tip noise are to be tackled and reduced as far as possible. It has been proven from wind tunnel experiments within a Dutch TWIN-project that in the 2d-case a reduction of up to 6 dB(A) can be achieved by the application of sawteeth. In an EU-project on tip noise it has been shown that the noise emission strongly depends on details of the flow and, therefore, the 2d-results cannot be transferred straight away to full-scale blades. At present no theoretical predictions or experimental data are available on sawtooth trailing edge noise for 3d-flow. The STENO project wants to close this gap.


Technical Approach

Since most of the aeroacoustic noise emanates from the tip region - here representing the outer 15% of the blade - the noise-reducing means should be applied there. With a special blade tip (supplied by Aerpac) measurements will be performed in anechoic and low-speed wind tunnels at NLR, both to find the aerodynamic input parameters needed for a semi-empirical noise prediction method and to measure the actually generated noise to be compared with the predicted one. With these results, an existing 2d-model for noise emission from serrated trailing edges will be extended at TNO/TPD to and validated for the case of 3d-flow in the blade tip region. It will then be used to lay out the optimum serration geometry for the full scale UNIWEX tips. It is planned to investigate three different tips experimentally on the two-bladed 16m UNIWEX turbine of the ICA/Uni Stuttgart. Operational, structural and acoustic data will be collected, the latter by ECN applying a proven far-field method. These results will lead to a quantitative ranking of the different tips and the prediction method. After possible modifications of the tips and/or selection of differing test parameters, a second round of experiments will be conducted.


Expected Achievements and Exploitation

The project proposed will assess the noise reduction potential of sawtooth trailing edges for full-scale wind turbines and will provide a semi-empirical prediction method which could be applied to the acoustically most interesting blade tips with 3d-flow. Up to now this method is only applicable to the more inboard blade sections with practically 2d-flow. This will allow the design of quieter wind turbines - 3dB(A) less if the 2d results of the TWIN project can be achieved for the 3d-flow as well - or even cheap retrofits for existing turbines. This would allow further areas (sites) to be used for wind energy production without violating existing legal regulations for acceptable noise level limits and would increase the general acceptance of wind energy by the public.

Coordinator

UNIVERSITAET STUTTGART
Address
Pfaffenwaldring 27
70569 Stuttgart
Germany

Participants (4)

Aerpac Special Products BV
Netherlands
Address
96,Bedrijvenpark Twente
7602 KD Almelo
ENERGY RESEARCH CENTRE OF THE NETHERLANDS
Netherlands
Address
Westerduinweg 3
Petten
NEDERLANDSE ORGANISATIE VOOR TOEGEPAST NATUURWETENSCHAPPELIJK ONDERZOEK TNO*
Netherlands
Address
1,Stieltjesweg 1
2628 CK Delft
Nationaal Lucht- en Ruimtevaart Laboratorium
Netherlands
Address
31,Voorsterweg
8316 PR Marknesse