ECN publication
Aerodynamic field data of a non-rotating rotor blade: acomparison to "2D Steady" data and an analysis of inflow conditions
Published by: Publication date:
ECN 1995
ECN report number: Document type:
ECN-C--95-063 ECN publication
Number of pages: Full text:
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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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