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.摘要：翼型后缘表面是宽带气动噪声的重要产生源。本文针对翼型后缘附近湍流边界层引发的三类翼型自噪声机理展开研究。针对叶片长度37 m、声源高度80 m的三叶2 MW水平轴上风式风力机，在8~15 m/s的风速范围内开展数值计算。针对位于距风力机总高度的位置、地面以上2 m高度处的接收点，计算了计权1/3倍频程带声功率级（Sound Power Level, SPL）。采用基准模型得到的声功率级结果显示，频谱峰值出现在300 Hz至1 kHz频段内。在10 m/s风速下，BPM模型的变化趋势显示在1 kHz频段附近声功率级降低约2 dBA；而Grosveld模型与Lowson模型的结果完全一致，在全频谱范围内吻合良好。针对2 MW风力机，在8 m/s风速下，采用三类基准模型分析了转速对声功率级的影响规律。结果表明，当转子转速相对于额定值变化±10%时，由于叶尖速度的差异，全频段声功率级将提升2~6 dBA。