Environmental Engineering Reference
In-Depth Information
Note that each blade loading harmonic
m
,
caused by fluctuating air loads, gives rise to more
than one sound harmonic
n
in the radiation field.
For the special case in which the inflow wind to the rotor disk is uniform and the
listener is located in the plane of the axis (
i.e.
,
f
=
0), Equation (7-la) reduces to
Ö
2 sin g
4 p
R
e
d
T
cos g -
Qa
0
R
e
W
M
n
J
nB
(7-2)
P
n
=
where
T =
rotor shaft thrust (N)
Q
= rotor shaft torque (N-m)
Example Rotational Noise Calculations
Examples of sound pressure levels calculated by means of Equation (7-1) for the Mod-1
HAWT are presented in Viterna [1981] and are included in Figures 7-12 and 7-13. The cal-
culations relate to the following geometric and operating conditions:
R =
30.5 m hub height,
H =
46 m
B
= 2 power output,
P =
1.500 kW
W = 34.6 rpm wind speed,
U =
13.4 m/s
d =
79 m and 945 m downwind deficit behind tower = 20 percent over a
20 deg sector
Figure 7-12. Measured and calculated rotational noise spectra 79 m downwind of the
Mod-1 HAWT.
(rotor diameter = 61 m, wind speed = 13.4 m/s, power output = 1,500 kW)
[Viterna 1981]
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