5. Conclusion

Figure 23. Cross spectrum of baseline airfoil with serration trailing edge.

142 Stability Control and Reliable Performance of Wind Turbines

Figure 24. The level difference of baseline airfoil with serration trailing edge.

A wind tunnel experiment was conducted on 2D airfoils, and the noise reduction effect was examined based on aerodynamic performance. Using the wind tunnel test on 2D airfoils with serrated trailing edges, wake distribution measurements and an analysis of their relationship with acoustic characteristics were conducted in order to examine the restrictive conditions of Howe's theory. These experimental results confirmed that as changes occur in the boundary layer thickness of 2D airfoils, an empirical formula or a theoretical approach which can reflect these changes is necessary. This study suggested an empirical formula for the prediction of noises in serrated trailing edges by utilizing the wind tunnel results on 2D airfoils with serrated trailing edges, based on the acoustic model suggested by Brooks. Also, the wind tunnel test results and noise prediction results of the NACA0012 airfoil with serrated trailing edges were compared with those of the baseline airfoil, and, through this comparative analysis, the study suggested a new noise prediction empirical formula for 2D airfoils. The study confirmed the validity of the proposed noise prediction formula by carrying out aerodynamic performance testing and noise measurements on the NACA0012 airfoil, the baseline airfoil, and the serrated trailing edges. However, as the noise prediction formula for the serrated trailing edges was an empirical formula that was based on limited experimental conditions, errors may have arose because of factors including the installation angles of the serrated trailing edges and the cross-sectional shapes of the 2D blades. To make up for the shortcomings in the test results, additional wind tunnel tests need to be conducted, and in consideration of the test results, further studies need to be conducted on the formation of a more accurate noise prediction formula.
