Abstract
Infrasound, i.e., low-frequency noise in the frequency range of 10–200 Hz, produced by rotating wind turbine blades has become a matter of concern because it is harmful to human health. Today, with the rapid increase of wind turbine size, this kind of noise is more worrying than ever. Although much effort has been made to design quiet wind turbine blades, today there is still a lack of effective techniques to reduce infrasound emissions from existing blades. To fill this gap in technology, a biomimetic technique that can be readily applied to reduce infrasound emissions of existing wind turbine blades is studied in this paper using both numerical simulation and experimental testing approaches. The numerical study of the technique is based on the analysis of the sound field distribution near the blade, which is derived by performing both aerodynamic and acoustic simulations of the blade. The experimental study of the technique is based on laboratory tests of two scale models of the blade. Both numerical and experimental studies have shown that the shedding vortices behind the blade can be successfully suppressed by semi-cylindrical rings wrapped on the blade. Consequently, both infrasound and the overall sound pressure level of the noise produced by the blade are significantly reduced. Although the rings fail to show good performance in reducing high-frequency noise, it is not a problem for human health because high-frequency noise is weak and moreover it attenuates rapidly as distance increases. The research also showed that the proposed technique can, not only reduce the infrasound produced by the blade, but can also improve the power coefficient of wind turbines.
Highlights
In response to the Paris Agreement of 2018, which calls on all countries to take responsibility for tackling climate change and keeping the global temperature rise below 1.5 degrees Celsius in this century, many countries have taken action to accelerate the development of wind power
The objective of this study is to develop a feasible post-processing technique that can be applied to reduce the infrasound of existing wind turbine blades, while not affecting their energy capture efficiency
With the increasing application of wind turbines, the infrasound produced by rotating wind turbine blades has become a matter of concern because they are harmful to human health
Summary
In response to the Paris Agreement of 2018, which calls on all countries to take responsibility for tackling climate change and keeping the global temperature rise below 1.5 degrees Celsius in this century, many countries have taken action to accelerate the development of wind power. Hundreds of thousands of wind turbine blades have already been installed and Energies 2021, 14, 4923 put into operation, and how to reduce the noise, especially infrasound, produced by these existing blades is still an open issue. This motivates the research of this paper. The proposed technique should not require any modification to the aerofoils and the structure of the blades The achievement of such a technique will fill the present gap of knowledge in the field of wind power technology and enable us to reduce the infrasound emissions from existing wind turbine blades by using a cost-effective post-processing technique.
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