Environmental Engineering Reference
In-Depth Information
Wind Turbulence Spectra in a Neutral Atmosphere
Analytical models for spectra of the longitudinal, lateral, and vertical components of
atmospheric turbulence are discussed in a number of references. Haugen [1973], and
Panofsky and Dutton [1984] give detailed physical and mathematical descriptions, whereas
Counihan [1975] and Frost
et al.
[1978] use an engineering handbook format. A modified
version of a spectrum model developed by Kaimal [1973] is as follows:
n
f
a
s
0,a
0.164 h/h
a
1 + 0.164(h /h
a
)
1.667
(8-16a)
=
h =
n z
U
(8-16b)
where
f
a
= power spectrum of wind fluctuations in the a direction at elevation
z
(m
2
/s)
a=
x
(longitudinal),
y
(lateral), or
z
(vertical) direction
s
0,a
= ambient turbulence in the a direction (m/s)
h
= normalized frequency
h
a
=reference normalized frequency, dependent on elevation and stability
Figure 8-17 is a graph of Equation (8-16a) for conditions of neutral stability, with the
following recommended values of the elevation-dependent reference normalized frequencies:
h
x
= 0.0144(
z
/30)
0.78
h
y
= 0.0265(
z
/30)
0.78
h
z
= 0.0962
(8-16c)
Figure 8-17. Modified Kaimal model of turbulence spectra at an elevation of 30 m.
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