Civil Engineering Reference
In-Depth Information
For the along wind
u
component the situation is illustrated in Fig. 3.3. It is taken for
granted that statistics performed on time series recordings of each of the
turbulence components will render three individual zero mean Gaussian probability
density distributions with variances
⎡ ⎤
2
⎡
2
()
()
()
⎤
ut
vt dt
σ
σ
σ
u
⎢ ⎥
T
⎢
⎥
1
2
2
∫
⎢ ⎥
=
⎢
⎥
(3.13)
v
T
⎢ ⎥
⎢
⎥
0
2
2
wt
⎢ ⎥
⎢
⎥
⎣ ⎦
w
⎣
⎦
Fig. 3.3
The probability distribution of the along-wind turbulence component
The corresponding turbulence intensities are defined by
()
()
z
σ
()
nf
Iz
nuvw
,,
=
where
=
(3.14)
nf
Vz
f
A typical variation of the turbulence intensity for the along wind
u
component is given
by
(
)
⎧
1/ln
zz
/
when
z
>
z
⎪
()
f
0
f
min
Iz
≈
(3.15)
⎨
uf
(
)
1/ln
z
/
z
when
z
z
≤
⎪
⎩
min
0
f
min
