Effect of Boundary Layer and Rotor Speed on Broadband Noise from Wind Turbines

Abstract

Trailing edge surface of aerofoil is an important source of broadband aerodynamic noise production. In this paper, three aerofoil self-noise mechanisms from turbulent boundary layer near trailing edge surface are studied. Numerical computations were performed for a three bladed 2 MW horizontal axis upwind turbine of blade length 37 m and source height of 80 m, for wind speeds of 8-15 m/s. A weighted 1/3rd octave band sound power levels (SPL) are evaluated for receiver located at distance of total turbine height and at 2 m above ground. The results obtained for sound power level using baseline models showed maximum values occurring between 300 Hz and 1 kHz region of spectrum. The trends for BPM model showed a reduction of ~2 dBA near 1 kHz region of spectrum at 10 m/s, but Grosveld’s and Lowson model were identical and agreed over the entire spectrum. The effect of rotational speed on sound power levels using three baseline models are illustrated at a wind speed of 8 m/s for 2 MW turbine. Results showed that for a change of ±10% rotor speed from the rated value, there is an increase of 2 to 6 dBA over the entire sound spectrum due to differences in blade tip speed.

Theoretical and Experimental Analysis of Aerodynamic Noise in Small Wind Turbines

“…In this work, a study of the noise emitted by a wind turbine of 1 kW installed in the Isthmus of Tehuantepec, Oaxaca, Mexico, was carried out, in which the sound pressure levels produced by the detachment of the turbulent boundary layer at the trailing edge were determined using the semi-empirical method proposed by Brooks et al [25] and the sound pressure levels due to the formation of vortexes at the tip of the blade generated by the rotation speeds of the wind turbine [17,26]. In order to validate the models' results, an experimental study was carried out using the recommendations of the IEC 61400-11 Standard [27].…”