A comparison of different approaches on the aeroacoustic noise radiated from airfoils for wind turbine blades
Date Issued
2009
Date
2009
Author(s)
Chang, Chieh-Shih
Abstract
The purpose of the research is to investigate the noises induced by flow over the wind blades. The noise analysis is conducted by the Broadband Noise Source Model and FW-H (Ffowcs Williams and Hawkings) Formula which are based on theory of Lighthill’s acoustic analogy. How the wind velocity, angle of attack as well as the inflow turbulent intensity influence the induced aerodynamic noise is discussed. First of all, the dynamic coefficients and flow field of three airfoils NACA64(3)-618、S809 and S822 were verified, and then the accurate information of turbulence was provided as the source to evaluate the sound energy distribution. Three types of noise models that provided different characteristics of the noise distribution were adopted in this wrok. Firstly Reynolds-averaged Navier-Stokes Equation with the k-e turbulent model was used to predict the turbulent flow field. When the inflow turbulent intensity was increased to 5% and 10%, it causes great changes to the flow field and obviously it is also one of the major facts to the flow induced noise. For aerodynamic noise analysis, Proundman’s BNS model was performed to get the acoustic energy density distribution over the entire calculating domain. Further, Curle’s Formula was adopted to predict the surface acoustic power along the solid boundary. In order to understand the details of flow induced noise one step further, the Large Eddy Simulation approach for the unsteady flow combined with the FW-H equation was used to predict the unsteady sound pressure signal. Then by Fourier Transformation the spectrum of the noise can be calculated and consequently the frequency distribution and the power output are achieved. It might be useful in reducing the flow induced aerodynamic noise. However, LES requires a very fine grid resolution to capture the large scale eddy. At this stage, our current computer resources are extremely difficult to satisfy the computational efforts. Therefore, only the small wind blades were taken as the analysis object in this study. This experience may be useful in large wind blade analysis in the near future.
Subjects
blade
aerodynamic noise
turbulence
broadband noise source model
FW-H equation
Type
thesis
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