Field experiment and analysis of the wakebehind a horizontal-axis wind turbine
2016
Wind turbines work in a complex natural environment, where their
flow field shows the characteristics of high turbulence levels. Due
to the complexity and instability of the atmospheric boundary layer
flow, as well as the influence of the scale effect, wind tunnel test
cannot reflect the real working condition of wind turbine. So field
experiments are very necessary to study wind turbine flow characteristics
in actual wind field. In this investigation, field experiments of
the wake behind a wind turbine were carried out to get velocity distribution
in it. The field experiment system is composed of a 33 kW wind turbine,
a 20 m high anemometer tower, a wake velocity measurement platform
and the controlling device. The wind turbine is horizontal-axial,
two-bladed, upwind-type, with variable pitch angles, 14.8 m in diameter.
Wake velocity measurement platform is composed of an 18 m high hydraulic
lift, anemometer installation platform and three sets of the US CSAT3
three-dimensional ultrasonic anemometer. Inflow parameters were gauged,
such as wind speed, wind direction, atmospheric pressure, temperature
and humidity. Besides, the operating conditions of the wind turbine
were recorded, including pitch angle, yaw angle, rotor speed. It is
discussed that the time domain and power spectrum characteristics
of wake velocity at a measuring point located at one rotor diameter
downwind from the rotor plane. The results show that there are larger
velocity deficits in the wake. The axial velocity deficit rate at
the measuring point is between 35.1% and 54.17%. The change of the
velocity in vertical direction is small. The velocity in lateral direction
is slightly larger than the velocity component of inflow, which reflects
the expansion characteristics of the wake. Besides, the turbulent
kinetic energy at the measuring point shows a periodic variation,
and the vortex sheet passage frequency is similar to the rotation
frequency of the wind turbine. Meanwhile, all of the power spectra
of turbulent velocity in three directions at the measuring point show
a characteristic of slope for –1 at the section of low frequency,
which mean the turbulent flow is in the classical production subrange.
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