Wind turbine acoustics - Wind Power Generation and Wind Turbine Design - page 159

Figure 5: Mechanical noise sources: air-borne noise (continuous arrows) and
structure-borne (dashed arrows).
Figure 6: Mechanical noise reduction using elastic fi ttings (after [ 5 ]).
To reduce the gearbox noise, proper teeth profi les and high accuracy products
are needed. To avoid amplifi cation of the noise by the casing, the casing has to be
designed to have eigenfrequencies far from the critical frequencies from the gears.
To avoid the transmission of vibrations, elastic couplings have to be used between
the mechanical devices. For large turbines, such couplings cannot transfer the
torque and the elastic coupling is mounted between the low-speed and the high-
speed stages of the gearbox. This approach is effi cient, since most of the noise is
coming from the high-speed gears, which can be elastically mounted using this
solution (see Fig. 6) [5]. Further reductions of the emitted noise levels can be
achieved by acoustic insulation of the nacelle.