Aerodynamic noise from wind turbines. Experiments with modification of full scale rotors, 2

摘要

Two series of measurements have been made where the noise from a wind turbine is measured during different modifications of its rotor. One series dealt with different shapes of trailing edge, while the other focused on the tip design. The investigations form a succession of earlier work and basically the same measurement technique was used. In the present investigation the pitch setting of the wind turbine was varied so that the significance of this parameter could be quantified as well. Measurement were made simultaneously of noise in the downwind direction and of the wind speed at 10 m height upwind of the wind turbine, both averaged over 1-minute periods. Regression analysis was made between the wind speed and the noise level in each 1/3-octave band in the range 50 Hz - 10 kHz. Intermittent background noise was omitted during the data collection, and stationary and wind-induced background noise was corrected for. The investigations of trailing edge noise gave no clear indication of an optimum trailing edge sharpness. The characteristic narrowband noise from trailing edge bluntness was demonstrated, and its dependence on trailing edge thickness, wind speed, and pitch setting was determined. The noise level of the narrowband has a 'reverse' wind speed dependence; it decreases with increasing wind speed (and increasing angle of attack). In the tip noise investigation three tip shapes were tested, the original thick square tips with slightly rounded edges, an elliptically rounded thin tip shape, and an Ogee tip designed after the most quiet tip tested in the previous project. The round tip was slightly more noisy than the square tip, and the Ogee tip gave rise to a broadband noise around 2 kHz where the wind speed dependence was again 'reversed'. (EG)