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Title:
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The April 95 procedure to measure the pressure coefficient Cp on a wind turbine in the field: with the December 1998 proposal for a Cp-derivation
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Author(s):
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Published by:
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Publication date:
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ECN
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1-12-1998
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ECN report number:
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Document type:
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ECN-RX--98-066
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Article (scientific)
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Number of pages:
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25
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Published in: Paper presented at the Annual IEA Symposium on the aerodynamics of wind turbines, December 3-4, 1998, Lyngby, Denmark (), , , Vol., p.-.
Abstract:
To study the three-dimensional flow around the rotor blades of windturbines, field experiments were carried out at DUT (Delft University of
Technology in Delft, Netherlands), at ECN (Netherlands Energy Research
Foundation in Petten, Netherlands) and at NREL (National Renewable Energy
Laboratories, USA). In all cases a test turbine was equipped with pressure
measurement equipment inside one of the blades. The purpose of the
experiments was to enable the description of the differences between the
pressure distributions on the blades while they rotate in the field (3d-flow)
and the pressure distributions on the same blade in the wind tunnel
(2d-flow). In 1992 the first measurements on the 10m diameter test turbine of
DUT were carried out. These measurements are described elsewhere and showed a
sinusoidal variation of 1P in all pressure signals. A damper was inserted in
the tubing at the reference side of the system in an attempt to suppress the
variation. However after this change, the variation was still present.
Therefore, after about two years of preliminary measurements, it was realised
that the measuring system required a more thorough analysis to improve and
understand the results. This report is written in that context. The primary
goal is to accurately predict both the loads on and the power of a wind
turbine rotor. Present prediction methods often are inaccurate and therefore
better understanding in the rotor aerodynamics is required. Power and loads
origin from pressure distributions over the rotor blades, for this reason it
was decided to measure these distributions. The measured local pressures on
the blades mostly are made dimensionless with the dynamic pressure, which
will be defined later. For the dimensionless pressure or pressure coefficient
the symbol cp is used. The local values of cp can be seen as the basic
information on the aerodynamic behaviour of wind turbines. Many other
relevant parameters, e.g. loads and power, can be derived from the
cp-values. For this reason this report will focus on the derivation of cp
from measured values. 8 refs.
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