Characteristics of the Wind - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 524

speed fluctuations have a Gaussian probability distribution, and the filter function h(t) is
designed to provide a time history with a prescribed turbulence intensity and power spec-
trum. The procedure for determining filter characteristics is given in Frost and Moulden
[1977] and Frost and Wang [1980]. Many of the early simulations used a Dryden spectrum
for simplicity, but recent models use spectra more representative of atmospheric turbulence.
The complex simulation system shown in Figure 8-34(b) generates time histories for
all three wind velocity components and is capable of matching considerably more statistical
properties than the simple system. Filter functions are selected so that the spectrum of each
component simulates that of a wind which contains large eddy fluctuations. Vertical
coherence requirements can also be satisfied by a simulation of this complexity.
It is apparent that the completeness of the turbulence simulation produced by the
transformation technique is basically dependent on the degree of mathematical sophistication
represented by the filters. Table 8-6 lists a number of reported turbulence transformation
simulations and the statistical parameters incorporated in each.
Figure 8-34. Schematic diagrams of turbulence simulations using the transformation
technique. (a) Simple one-dimensional simulation (b) Three-dimensional complex system