Abstract
With rising demand for energy and depletion of non-renewable sources, new avenues of energy production are being explored. Wind energy is one popular alternative to meet the energy needs of the future. Apart from visual impact and dependence on strong wind conditions for good performance efficiency, aerodynamic noise from wind turbines serves to be a major obstacle for their societal acceptance. This study tries to understand the propagation of wind turbine noise to the far-field, particularly in the lower frequencies using a technique based on inverse acoustic methods, the Acoustic Intensity Based Method(AIBM). At first the far-field noise radiation from NREL S809 airfoil is predicted using AIBM coupled with 2-D Computational Fluid Dynamics (CFD) simulations. Aeroscoustic characteristics of NREL Phase VI Horizontal Axis Wind Turbine rotor is then analyzed using AIBM. The flow field in 3-D is obtained by solving the Unsteady Reynolds Averaged Navier-Stokes Equations (U-RANS). The CFD results of the flow field are validated against experimental data and they show good agreement. Thickness noise, created by displacement of a mass of air by the rotating blades, and loading noise, created by the rotor interacting with local flow deficiencies, are identified as the two causes of low frequency noise based on the calculated directivity patterns. The ultimate objective is to create a hybrid tool to predict far-field noise from a given set of flow field data obtained experimentally or numerically, using AIBM.
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