Prediction of Aerodynamic Noise Generated By Wind Turbine Blades

Abstract

The preliminary step in the computational study of mitigating the aerodynamic noise generated by wind turbine blades involves accurate prediction of aerodynamic noise generated by a wind turbine rotor which can be used a basis for comparison. The NREL Phase VI HAWT rotor has been chosen to perform this study. This is achieved by first predicting the three dimensional flow field around the rotor through CFD analysis using SST k-ω turbulence model for wind speeds of 7m/s, 10m/s, 13m/s and 15m/s. CFD analysis has been performed using the rotating reference frame method at steady state conditions which resulted in predicting the flow field accurately with less computational time. The rotational periodic boundary condition with 1800 symmetry has been used with which one blade has been simulated instead of two. This reduced the mesh size and thus computational costs to perform the CFD analysis. To validate the prediction of flow field obtained through CFD analysis, performance characteristics and aerodynamic characteristics such as torque generated and trends of pressure coefficients at different span locations are validated against the time averaged experimental results and other results pertaining to the same published in previous computational study. The results obtained through CFD analysis show good agreement with both experimental results and previous computational results. Based on the trends of pressure coefficients predicted for different wind speeds we see that it is most accurate at a wind speed of 7m/s and this accuracy gradually decreases with increase in wind speed. Once the flow field was accurately predicted, this was used to predict both the location and magnitude of aerodynamic noise generated by the blade using the Curle broadband noise source model. Aeroacoustic analysis indicates that major noise sources are located near the tip of the blade and it gradually decreases as we move towards its root. This trend is observed at all four wind speed conditions. It is also observed that with increase in wind speeds, there is increase in the intensity of noise generated by the blades and thus increase in Sound Power Level across the blade.