Jang-Oh Mo1 and Young-Ho Lee2,*
The Journal of Mechanical Science and Technology, vol. 25, no. 5, pp.1341-1349, 2011

Abstract : The purpose of this study is to numerically predict the characteristics of aerodynamic noise generated from rotating wind turbine blades according to wind speeds using commercial CFD code, FLUENT. The near-field flow around a HAWT of NREL Phase VI is simulated directly by LES, whereas the far-field aerodynamic noise for frequencies below 500 Hz is modeled using FW-H analogy. As there was no experimental noise data, we first compared aerodynamic noise analysis with experimental data. This result showed a difference of power outputs by 0.8% compared with the experimental one with 6.02 kW. Then the characteristics of aerodynamic noise were predicted at a specific location P1 according to IEC 61400-11 international standard. When the wind turbine blades rotate with time, tipvortices occur at the tip of two blades and are generated periodically in a circle. These vortices in the vicinity of the blade tip cause intense aerodynamic noise due to the tip vortex-trailing edge interaction by local cross flows along the trailing edge. In a wind speed of 7m/s the sound intensity ratio of quadrupole to dipole at P1 location is about 21.1%, but as wind speed increases the sound intensity ratio increases up to 54.3% in the case of no-weighted correction. This means that there is a considerably close relation between the quadrupole noise by small and large scales and the increase of wind speeds. With the purpose of a rough prediction of sound power level, CFD results were compared with a simple model of previous researchers and showed a good agreement with one by Hagg of three other models.

Keyword : CFD; Large eddy simulations; FW-H analysis; Aerodynamic noise; Sound pressure level; Dipole; Quadrupole; Tip vortex; Horizontal axis wind turbine; Overall sound pressure level; A weighted correction