Environmental Engineering Reference
In-Depth Information
Turbulence Modeled From a Rotational Frame of Reference
Previous discussions have dealt with turbulence measured at a single point or a multiple
of fixed points along a line in space. This type of turbulence modeling, in which the refer-
ence coordinate axes x-y-z are fixed in space, is also called Eulerian. Since the late 1970s,
considerable study has been carried out by wind energy researchers on measuring and
modeling fluctuations in the wind from a rotating or Lagrangian frame of reference.
Starting in 1977, personnel at the Battelle Pacific Northwest Laboratories in Richland,
Washington, began studies of the wind as seen by a rotating turbine blade passing
repeatedly through a wind field with spatial and temporal fluctuations. Measurements have
been made using fixed arrays of towers and anemometers [Verholek 1978, Connell 1981,
George 1984, George and Connell 1984], a rotating-boom hot-wire anemometry system
[Sanborn and Connell 1984], and a lidar scanning system [Hardesty et al. 1984].
Vertical Plane Arrays
The test installation shown
schematically in Figure 8-27 [Ver-
holek 1978] is typical of the so-
called vertical plane arrays . In-
strument towers along a line per-
pendicular to the prevailing wind
support a circular pattern of ane-
mometers at equal intervals. This
particular anemometer circle repre-
sents the path followed by a blade
section 12.2 m from the rotor axis.
The wind velocity sensed by each
anemometer is continuously record-
ed. By joining segments of wind
speed records taken sequentially
from consecutive anemometers
around the circle, the time-history
of wind velocity experienced by a
section on a rotating blade can be
synthesized. The length of the
segment from each anemometer
depends on the tangential speed of
the hypothetical blade section.
Figure 8-28 illustrates typical
rotationally-sampled wind speed
data. In Figure 8-28(a), the domi-
nant fluctuations with a period
equal to the period of rotation (0.8
s) are caused by the mean wind
shear profile. Also evident are
higher-frequency fluctuations which
indicate the non-uniform structure
of the small-scale turbulence mea-
sured at the various anemometers
along the circle of rotation. Such
Figure 8-27. Schematic diagram of a vertical-
plane array of anemometers for measuring tur-
bulence experienced by a rotating HAWT blade.
Sampling of signals from anemometers 2 to 9 is
synchronized with the passage of blade section A .
[Verholek 1978]
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