With alternative energy becoming more prevalent the acoustic impact of machinery used to generate the energy is of interest. The noise produced from wind turbines is an important factor in the design as it can affect nearby communities. A numerical tool has been developed to predict the unsteady thrust and directly radiated noise from a single or multi-blade row turbomachine, which can easily be applied to a wind turbine.
The tool, called TONBROD, can predict blade rate and turbulence ingestion noise, however only the latter is of concern for this work. An asymptotic approach is used to quickly and efficiently predict the unsteady force on each blade from the chopping of incoming turbulence (e.g. turbulence ingestion noise). This force is then used to estimate the radiated noise. A user can prescribe the incoming turbulence intensity (circumferentially and radially varying) and integral length scale (circumferentially uniform but radially varying) that is then modified by the upstream blade row and advected to the downstream blade row through semi-empirical formulations. A prediction of the resulting unsteady force and noise is then made for either blade row. The asymptotic theory is briefly discussed and then the prediction of radiated noise for both homogeneous and inhomogeneous turbulence is compared to experimental data. It is shown that the method provides good results.
