**1. Introduction**

Wind power is growing at exponential rate with installed wind power capacity reached more than 500 GW globally. By far the cheapest source of energy generation among all renewable energy technologies is wind power. As more wind power projects are installed, a growing concern of noise emissions from wind turbine blades is increasing due to adverse health effects on inhabitants living near wind farms [1]. Many policy makers are considering this issue seriously as noise generated from wind turbines is an impediment to the growth of wind energy growth. Modern megawatt scale turbines have large rotor diameter of size 100 m and above which contribute to the overall noise levels and cause annoyance for people living

near wind farms. **Figure 1** depicts the evolution of size of horizontal axis wind turbines over the period of forty years. Size of rotor diameter ranges from 17 m to 165 m with its nominal power range between 70 kW to 6 MW.

Airfoil self-noise from wind turbines with longer blades have higher tip speeds and produce high aerodynamic noise. Studies by several researchers have found that most of the broadband aerodynamic noise emissions occur due to trailing edge source from rotating blades such as from helicopter, wind turbines and compressors [2–5]. However when the blades become thicker, the trailing edge bluntness source also dominates between moderate to high frequency range in noise spectra. Airfoil self-noise prediction models developed by Brooks Pope and Marcolini (BPM) have been studied and improved by several researchers [6–8]. One of the recent improvements in the trailing edge bluntness noise predictions was done by Wei et al. (2016) who applied numerical techniques and correlated their results with field experiments measured for Siemens 2.3 MW wind turbine blade. They also used computational aero-acoustic (CAA) method to compute the trailing edge bluntness noise level from NACA 0012 airfoil with finite thickness for consistent validation of results obtained from BPM semi empirical noise prediction model and measured noise data. In addition, NACA 63–418 with two different variants of trailing edge shapes were studied to compare the noise spectra. They modified the generalized shape function proposed by original BPM model and made it independent of the solid angle formed between the trailing edge surfaces of airfoil to investigate the effect of the shape function on the trailing edge tonal noise peak produced in the high frequency region of sound spectra. In the present study, we investigate the shape function used by BPM model for predicting the trailing edge bluntness noise source but also apply regression approach to improve the bluntness peak at the high frequency region of noise spectra. To the best of authors knowledge, regression approach has not been implemented before to study the effects of trailing edge tonal noise source for wind turbine blades. In Section 2, we describe the trailing edge bluntness noise method developed by BPM along with present formulation. In Section 3, geometry model of wind turbine blade used in study is described along with IEC 61400–11 standards for measurements of acoustic emissions for wind turbines. Computational assumptions are described for the generating aerodynamic flow field by means of BEM which is coupled to the noise solver for predicting sound power level. The noise solver for the trailing edge bluntness source is

**Figure 1.** *Illustration of size of horizontal axis wind turbines (HAWT) and its evolution over a period of forty years.*

*Trailing Edge Bluntness Noise Characterization for Horizontal Axis Wind Turbines [HAWT]… DOI: http://dx.doi.org/10.5772/intechopen.99880*

developed based on the original BPM model along with its improvements proposed by [9]. Regression method is then applied on trailing edge noise shape function based on the coefficients obtained for the modified trailing edge height of the airfoils along the span wise direction of blade. In Section 4, present results for trailing edge bluntness noise source are compared to those obtained from original BPM, modified BPM by [9]. Overall 1/3rd octave band sound power level for the 2 MW wind turbine with a blade length of 38 m are computed and validated with experiment data of the GE 1.5sle, Siemens SWT 2.3 MW with 93 m, 95 m, and 101 m versions of turbines. Finally, conclusions are presented based on the results obtained for the original BPM, modified BPM and present correction function for airfoil thickness to chord ratio.
