Experimental Validation of a Wind Turbine Turbulent Inflow Noise Prediction Code

This paper describes the comparison of a semi-empirical wind turbine noise prediction code to a large volume of acoustic data gathered on a full-scale 2.3 MW wind turbine. Particular focus is placed on the turbulent inflow noise model due to the relatively small amount of validation that has been performed previously. Two novel techniques are developed in order to effectively validate the model. The first is that the turbulence is characterized in the acoustic model using a single quantity, the turbulence dissipation rate, instead of the combination of turbulence intensity and integral length scale as has been used in previous studies. The second development is a method of measuring the turbulence dissipation rate using blade-mounted accelerometers such that the turbulence dissipation rate in the vicinity of the blade is accurately determined. Using these methods, it is shown that the flat-plate airfoil analytical turbulence noise model underpredicts the turbulent inflow noise levels by 3-5 dB, whereas semi-empirical corrections for finite-thickness airfoils reduce prediction errors to less than 3 dB. Comparisons are also made on the basis of scaling with blade tip-speed, scaling with turbulence dissipation rate, and noise directivity.