Wind Turbine Acoustics - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 452

from the Mod-1 HAWT. The latter data fit within the body of test data on which the Inter-
national Standards Organization composite guideline is based. Therefore, they generally
confirm the applicability of this guideline for structural vibrations induced by wind turbine
noise.
Note that if measured vibration levels are not available they can be estimated for typical
house building elements from Figure 7-36, provided the external noise excitation levels are
known.
Figure 7-39. Most sensitive threshold of perception of vibratory motion. [Stephens et
al . 1982]
Measuring Wind Turbine Noise
Wind turbine noise is measured to define source characteristics, to provide acoustic
information for environmental planning, and to validate compliance with existing ordinan-
ces. It is important to use the appropriate equipment and measurement procedures and to
acquire data under appropriate test conditions. Measuring noise from wind turbine gener-
ators is particularly difficult because of the adverse effects of the wind [Andersen and
Jakobsen 1983, Jakobsen and Andersen 1983]. As a result, a number of special consider-
ations are involved in selecting measurement locations and equipment and in recording and
analyzing data. This section presents some guidelines on each of these subjects.
To make meaningful comparisons of the noise outputs of different wind turbines and
evaluations of environmental noise control, it is necessary to have generally accepted
standards of measurement. AWEA [1988], IEA-WECS [1988], and IEC [1998] contain
the results of work in the wind energy community to develop such standards. These
documents address significant issues in the measurement of wind turbine noise.
To interpret acoustic measurements, it is usually necessary to simultaneously record
various non-acoustic quantities. Among these are wind speed and direction, ambient
temperature and relative humidity, rotor speed, power output, time-of-day and date, type of
terrain and vegetation, and amount of cloud cover. Atmospheric turbulence (which is often
difficult to measure directly) may be inferred from this information.