Wind Energy

274 D. Moroianu and L. Fuchs
Amplitude
0.01
0.0001
Acoustic density fluctuation spectra Acoustic density fluctuation spectra
1 10 100 1
f/fBPF number
Y1
Y6
Amplitude
0.01
0.0001
71 72 73 74
76
75
70
10 100
f/fBPF number
Z1
Z6
69 68 67 66 65 64 63 62
Fig. 50.3. Acoustic density fluctuation spectra (above left and right); Instantaneous
acoustic density fluctuation (below left); Sound pressure level (below right)
The corresponding sound pressure level (SPL) field is depicted in Fig. 50.3
(below right). As expected, in the far field the SPL intensity decreases as if
the wind turbine is a point source. The isocontours become almost spherical
at a distance of about 3D. The interferences from the ground in the far field
are also weak and cannot be observed in the sound pressure levels.
50.3.3 Conclusions
The focus of the present work has been on the computation of the flow around
a wind turbine as well as on the spreading of the sound that it generates. The
vortex dynamics have been found to be in agreement with experiments. In
order to compute the noise generated by the turbine, an acoustic analogy has
been used. The acoustical field close to the wind turbine is dominated by
the rotation frequency of the blades (BPF). In the far field the spectrum is
influenced by the ground so different modes are stronger. There is a decay in
the amplitude of the sound with the distance and far from the wind turbine,
the acoustical waves are spread spherically as if they are coming from a point
source. The influence of the mast in the process of generation and propagation
of sound is not so strong. To asses the influence of terrain irregularities or air
dissipation, further work is required.
References
1. Brentner, K. S., Farassat, F., “Modeling Aerodynamically Generated Sound of
Helicopter Rotors”, Progress in Aerospace Sciences 39, pp. 83–120, 2003
2. C.G. Helmis, K.H. Papadopoulos, D.N. Asimakopoulos, P.G. Papageorgas, “An
experimental study of the near-wake structure of a wind turbine operating
over complex terrain”, Solar Energy, vol. 54, no. 6, pp. 413–428, 1995; 0038-
092X(95)00009-7