Wind Energy

f Suu(f, z) / σ 2 u(z)
10 0
10 −1
10 −2
10−3 10−3 10 −2 10 −1
6 Fluid Flow over Complex Terrain 35
Kaimal (1972) et al.
Simiu & Scanlan (1986)
Harris (1971)
Oleson (1984) et al.
experimental results
f z/u
10 0 10 1
Fig. 6.3. Spectral density distributions of the kinetic energy of turbulence
Table 6.1. Dimensionless recirculation lengths
Recirculation length ( L
W )
Measurement 0.63
k − ɛ RNG 0.66
k − ω SST 0.60
LES-SL 0.64
density distribution shows a maximum at higher frequencies in comparison to
the distributions given in literature (Fig. 6.3).
The three-dimensional hill model has been mounted on a flat plate which
extends over the entire length and width of the test section. The hill has a
height H of 100 mm and a half width W of 250 mm which leads to a charac-
2
teristic half-width to height ratio of 2.5. The measurements have been carried
out with a free stream velocity of 4 m
s .
6.3 Results
The numerical calculations have been performed with a commercial unstructured
finite-volume solver which employs a collocated grid. For all equations a
second-order upwind discretization scheme was used, while the pressurevelocity
coupling has been done with the SIMPLE method. Several turbulence
models and some of their variations have been employed [3]. The grid has been
refined up to the wall reaching dimensionless wall distances of y + � 4 − 11 in
order to be able to represent the recirculation zone in the lee of the hill.
The k − ɛ RNG and the k − ω SST turbulence model calculate the length
of the recirculation zone in the lee of the hill in good agreement with the