City Research Online

Abstract

The trend towards wind farms in Europe has brought with it a requirement for quieter wind turbines in order to satisfy planning constraints, and to obtain subsidy bonuses. The aim of the present work is to enable the redesign of a wind turbine for reduced noise emission whilst maintaining the same output power. This can be achieved largely by reducing the aerodynamic noise though appropriate blade redesign and establishing new procedures for the design of blades which take into consideration the specific characteristics of the wind turbine itself. Also it is important to understand the nature of such noise and the effect of various parameters on the overall noise level; thus the mechanical noise contribution may be identified and reduced through well known techniques. The noise structure of wind turbine generators has been investigated and a survey has been made to identify the major source of the noise and effect of each source on the overall noise level. This has enabled the development of a computer model that allows noise synthesis from geometric and engineering data to be predicted. A computer program entitled WTGNOISE has been written which embodies the noise model; this predicts wind turbine generator noise with acceptable agreement with measurement.

The program verification made use of detailed noise emission measurements made on the experimental downwind machine at Lords Bridge near Cambridge under a variety of conditions.

It is shown from the measurements carried out that the noise level from the machine is similar to that predicted by the mathematical model, especially the aerodynamic part. The difference between measured and predicted noise level is due mainly to mechanical noise. From use of the WTGNOISE it is seen that the reduction of peak aerodynamic pressures on the blades will have a large effect on the noise level emitted from the wind turbine. By appropriate changes to the geometry and the aerofoil design the peak pressure on the blades can be reduced leading to a reduction in the noise level. Application of the code to Garrad aerofoils GHP1, GHP2 shows that the noise level due to aerodynamic sources can be reduced while keeping the output power the same. Also upwind rotors are shown to have an advantage over downwind rotors from the noise point of view. Applying the knowledge acquired in current research in the case of a wind farm design, it has been found that a group of large machines produces a higher noise level than the equivalent number of smaller machines; thus, there are advantages from a noise point of view in using smaller rather then larger machines.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Engineering > Mechanical Engineering & Aeronautics School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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