Wind Energy

184 S. Dovgy et al.
33.2 Experimental Installation and Models
In Institute of Hydromechanics NASU, a mechanism has been proposed for
controlling the blades position during their movement on a circular trajectory.
To research features of operation of a windrotor with such mechanism and compare
the results with performance of geometrically similar windrotors with
rigidly fixed blades, an experimental setup and several windrotor models
with vertical axis have been created.
The windrotors models No. 1 and 2 had different diameter of a circle, on
which the axis of blades were placed on the rotor’s cross-arms. The number of
blades on each model changed during researches from 2 to 4, the blade profile
has been chosen axially symmetric of the type NACA-0015.
If blades were fastened on the windrotor cross-arms rigidly (the classical
scheme of Darrieu rotor), than the angle of the profile chord of blade to the
tangent to rotation circle was equal to +4 ◦ . The mechanism of blades control
provided angular oscillations of blades relative to the blade axis and during
one revolution the angle of blade installation changed from −14 to +25 grades.
For recording the investigated parameters of rotation of the windrotor
model, an automated measuring system of data gathering and processing was
used that is a digital storing oscillograph on the basis of the 12-digit 32-channel
analog-digital converter L-264 of the firms “L-Card,” assembled in the form
of an enhancement board of an IBM-compatible computer. The measuring
system consisted of three measuring channels.
During experiment the flow velocity Vav in front of the rotor, the revolution
velocity “n” of the rotor, and the torque M on the windrotor model shaft were
recorded. The magnitude of torque M increased until the model stopped.
33.3 Performance Characteristics of Windrotor Models
On the basis of ensemble-averaged values of flow velocity in hydrotray Vav,
rotational velocity “n” of the model, values of the loading torque M on the
model shaft, and also geometrical parameters of the models, we calculated
such windrotor characteristics as the coefficient of specific speed of windrotor
Z=2π n R/V, operating ratio of flow energy Cp =2πnM/ρV 3 Rlbl, and
coefficient of rotor torque Cm = Cp/Z, where lbl is the blade length, ρ is
density of water.
At constant flow velocity, with increase of the loading torque M on the
model shaft, all rotors have a reduction of rotational velocity “n” of the rotor,
but the level of this reduction depends on the rotor design. Rotational velocity
decreases faster in rotors with smaller number of blades. Rotors with
the mechanism of blade control showed slower speed than rotors with rigidly
fixed blades. The reduction of the radius R of the circle on which the windrotor
blades axes move leads to more essential reduction of rotational velocity “n”
of the rotor, and consecutively to an increase in the loading torque M at shaft.