Offshore Winds - Wind Energy Meteorology: Atmospheric Physics for Wind Power Generation - page 119

Fig. 5.26 Relative frequency of turbulence length scale in m at 80 m height at FINO1 in the
German Bight for the year 2005

Table 5.2 Stability dependent turbulence length scales, K Smax at 80 m height at FINO1
determined from maxima in the spectra for the three wind components (taken from Türk 2008 )
z/L \ -1 -0,1 \ z/L \ 0,1 z/L [ 1

K Smax (m) K Smax (m) K Smax (m)

u 290 485 292

v 252 286 223

w 223 97 15

The higher values for low wind speeds result from situations with high wave ages
(see Sect. 5.1.3 ). These high wave ages are most frequent with low wind speeds.
Figure 5.25 shows that the normalised variance increases with wave age for low
wind speeds. Such an increase has been reported by Davidson ( 1974 ) as well.

5.4.3 Turbulence Length Scales and Inclination Angles

Another parameter characterizing the spatial scale of the turbulence elements is the
turbulence length scale. Turbulence elements which are of similar size as the
turbine rotor often hit the rotor only partially and cause differential loads on
the rotor. Turbulent length scales have been determined according to the procedure
sketched in Sect. A.6 of the Appendix. Offshore turbulence length scales vary from
302 m for the longitudinal component (Fig. 5.26 ) via 273 m for the transverse
component to 41 m for the vertical component. These length scales can also be