Wind Energy

272 D. Moroianu and L. Fuchs
0.8
0.6
0.4
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0.2 0.0
e
h
a
d
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f
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g
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2.5D
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y
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D
H
D
2D 2D 2.5D
Fig. 50.1. Flow (left) and acoustical (right) computational domains
condition on face efgh - constant pressure and a turbulence intensity of
I = 4% is imposed, free stream boundary conditions on faces bcgf, dcgh
and adhe, the rest of the surfaces (abfe and the surface defining the wind
turbine) are wall boundary conditions.
The flow computational domain is included in a box with the following
dimensions: L1 = L2 =1.54 · D and L3 =0.38 · D; where D = 26[m] is
the rotor diameter. The position of the rotor above the ground is H
D =0.8.
The cross section profile is from a NACA 4415 airfoil. The blade is twisted
to keep a constant angle of attack of 7 ◦ . The spatial discretization of the
domain was based on an estimation of the Taylor length scale outside the rotor
and near the blade. The computational domain of the acoustical problem is
much larger than the computational problem of the flow field, and the farfield
of the acoustical field is depicted schematically in Fig. 50.1 (right). The
boundary conditions that are set for the acoustical problem are as follows: on
all boundaries, non-reflecting conditions are set, whereas on the ground, fully
reflective conditions are imposed.
50.3 Results
50.3.1 Flow Computations
The flow contributes to the noise sources mainly at regions of large gradients
in the flow as at the tip of the blade which is an important generator of shear.
This vortices are formed due to the pressure difference between pressure and
suction side of the blade and they are extended backward transported by the
flow in a spiral mode, as seen in Fig. 50.2. They are interacting with the mast
and with the vortices that are developing behind it.
8D
H
5D