Abstract
Models of inflow-turbulence noise and turbulent-boundary-layer trailing-edge noise are compared to earlier measurements of a 200-kW vertical axis wind turbine so that conclusions regarding the origin of the aerodynamic noise can be drawn. The measurement campaigns, which aimed at establishing the noise emission value and locating the aerodynamic noise sources with a microphone array, are here both compared to further modified versions of the trailing-edge and inflow-turbulence models respectively. Unlike the case for horizontal axis wind turbine, inflow-turbulence noise is deemed as the prevailing noise mechanism. Reducing the self-induced turbulence could then be an effective way of lowering the noise levels for vertical axis wind turbines. Also, looking at the directivity of the inflow-turbulence noise model which indicate most noise in the cross-wind directions, a deviation from the standard downwind measurement position for measuring noise emission is suggested for the VAWT case.
Highlights
Wind turbines can be categorized by the orientation of their axis of rotation into two groups: horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs)
To investigate which noise source is the most important for the T1-turbine, models for the turbulent-boundary-layer trailingedge (TBL-TE) and inflow-turbulence noise are compared with measured results from the noise emission and microphone array campaigns
Most noise is emitted when the blade is moving toward the wind for both models, and both models show a directivity that, for each blade position, suppresses noise if the observer is behind the blade and precisely in line with the blade chord. (For the inflow-turbulence model, noise is suppressed at the corresponding position ahead of the blade, see Eq (2).) Summing up the contributions over the whole revolution, the inflow-turbulence model shows a sharper directivity pattern, due to the narrow region where the blade interact with self-induced turbulence
Summary
Wind turbines can be categorized by the orientation of their axis of rotation into two groups: horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs). Different sub-concepts of both HAWTs and VAWTs have had individual threads of development in both Europe and North America [1,2,3]. It was mainly one of these sub-concepts, the upwind 3-bladed HAWT that established itself on the market in the 1970-80s in Denmark, where it thereafter has developed into the large and economically feasible wind turbines of today. The wind turbine industry is today facing several challenges, for example, local environmental impact as well as service cost and reliability These challenges match some of the possible advantages of the VAWT technology, which has led to a renewed interest in the concept.
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