Development and Validation of a Semi-Empirical Wind Turbine Aeroacoustic Code

A semi-empirical aeroacoustic noise prediction code for wind turbines was developed by integrating six different noise models into an aeroelastic simulation code. The code predictions were validated against experimental data from wind tunnel tests of airfoils and field tests of an operating turbine. For an S822 airfoil in steady flow, differences between predicted and measured sound pressure levels were 10 dB or less, but as large as 20 dB in turbulent flow. Relative trends in the measured airfoil data were reproduced by the code. For a 600 kW turbine, the predicted sound pressure levels were within S dB of measurements under most operating conditions. The relative change in measured sound pressure level between two observer positions was accurately estimated by the code, but the influence of directivity was overestimated. Increasing blade pitch towards feather decreased the amplitude of noise emitted from the turbine, which the code failed to predict. The measured and predicted overall sound pressure level of the turbine increased with mean wind speed. The prediction overestimated the measured values at lower wind speeds because of errors in the turbulent inflow noise model. Further research into turbulent inflow noise is necessary to improve the accuracy of the prediction code.