Empirical method of determining vortex induced aerodynamic noise from wind turbine blades: A computational approach

A dominant aerodynamic noise source from lifting surfaces occurs from trailing edge section of an airfoil as found in wind turbine blades. Computational analysis of trailing edge bluntness noise mechanism is demonstrated for a three bladed 2 megawatt wind turbine using empirical method proposed by Brookes, Pope, Marcolini (BPM). The method predicts the 1/3rd octave band sound pressure level from trailing edge bluntness source using boundary layer displacement thickness on pressure and suction side of airfoil. For low Mach number flows (0.1884) and moderate Reynolds number (4.73 x 105 - 3.35 x 106) in span wise direction of blade, turbulent boundary layer on the trailing edge surface is responsible for noise production. The trailing edge thickness effect on sound power level is illustrated for wind speed regime between 8 and 20 m/s. The results showed that sound levels increase for higher values of free stream velocity but blunt trailing edge noise source becomes insignificant when the trailing edge height scales to lower values of chord length. The computed results also confirm good agreement between overall A-weighted sound power levels and experiment data available for GE 1.5sle turbine with a rotor diameter of 77m at wind speed of 8m/s and 10m/s. The extent of reduction in sound power level was analysed using the trailing edge thicknesses scaled to 0.1 %, 0.5 % and 1% chord lengths at hub height wind speed of 8m/s and 10m/s.