Wind Turbine Noise Modelling Based on Amiet's Theory
Abstract
Broadband noise generated aerodynamically is the dominant noise source for a modern wind turbine(Brooks et al, 1989; Oerlemans et al, 2007). In this paper, two main broadband noise mechanisms, namely trailing edge noise and turbulent inflow noise, are examined in detail using frequency domain noise prediction models based on Amiet's analytical theory. Improvements are proposed to adapt the original model to wind turbines . First, a wall pressure spectral model proposed recently by Rozenberg, Robert and Moreau that considers an adverse pressure gradient flow (APG) is applied to the trailing edge noise model. This APG model leads to a significant increase in the sound pressure level. Second, an empirical airfoil thickness correction is proposed in the turbulent inflow noise model, which introduces a level reduction that depends on leading-edge thickness, frequency and the ratio of the turbulence integral length scale to the blade chord. The proposed model also includes Doppler effect for rotating blades. Calculation results are validated by comparison with wind tunnel experimental data and with measurements for a full size wind turbine. This model is also used to quantify the amplitude modulation that can be a source of annoyance in the vicinity of a wind farm.
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