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Title:
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Aerodynamic field data of a non-rotating rotor blade: acomparison to "2D Steady" data and an analysis of inflow
conditions
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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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1995
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ECN report number:
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Document type:
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ECN-C--95-063
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ECN publication
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Number of pages:
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Full text:
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58
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Download PDF
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Abstract:
Aerodynamic data obtained at a non-rotating rotor blade is different fromtwo-dimensional and steady data. In order to quantify the reasons for the
differences, five potential effects were identified. The effect of a spanwise
flow due to the shape of the rotor blade was investigated by introducing an
equivalent two-dimensional angle of attack on basis of a lifting line method.
The effect of the wind speed and the variation of the wind speed was
investigated by conditionally sampling the measured normal force coefficients
against the Reynolds number and the dimensionless wind-speed flux,
respectively. No significant difference between the normal force coefficients
in the various intervals was found. The effect of the boundary layers being
turbulent over a larger distance was investigated computationally by fixing
transition close to the position of the stagnation point. The results show
this leads to too small a value of the normal force coefficients, as compared
to the measured values. The effect of a natural spanwise flow due to the
environment of the rotor blade was investigated by mounting end plates
adjacent to a rotor blade section. No evidence was found of a natural
spanwise flow significantly affecting the measured data. This implies that it
is not possible to understand the effect of a three-dimensional and unsteady
flow towards a non-rotating rotor blade. The '2D steady' reference data was
obtained from computations with a modified version of the aerodynamic
analysis programme XFOIL. It must be noted that this tuning procedure
introduces an uncertainty of its own because the optimal boundary layer
parameters for a given geometry and Reynolds number combination might not be
optimal for a different combination. The data obtained at the non-rotating
rotor blade agrees qualitatively with the data obtained at a stopped rotor.
This implies there is evidence that '2D steady' data is an erroneous
reference to aerodynamic field data under non-rotating conditions. As a
consequence, care must be taken when applying '2D steady' data to a parked
rotor. 18 figs., 10 tabs., 16 refs.
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