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ECN publication
The Stall Flag method: proof of concept
Published by: Publication date:
ECN Solar Energy 1998
ECN report number: Document type:
ECN-RX--98-001 Article (scientific)
Number of pages:

Published in: Paper, presented at the joint ASME/AIAA wind energy symposium, Reno, USA, January 12-15, 1998 (), , , Vol., p.-.

The stall behaviour of large commercial wind turbines could not yet bemodelled reliably, because a measuring technique, that could visualize the stalled area on the rotor precisely in location and in time and directly on these turbines, did not exist. Therefore, detailed model validation was impossible. A new measuring method is being developed since 1994, based on a new detector: the stall flag (international patent pending). This so-called 'stall flag method' enables detailed visualisation of the entire stalled area on large wind turbines. Meant to serve as 'proof of concept', the stalled area of one blade of the 28m diameter test turbine of ECN was visualised with 57 stall flags. Pasting the stall flags on this blade took only three hours, proving the high applicability on a middle sized turbine (28m diameter). Aerodynamic results are that the range of the stall delay at the blade root in both radial and chordwise direction was observed. Then the stall flag patterns revealed that the stall behaviour was influenced by instrumentation used for other experiments. Finally the stalled fraction of the swept area at 300 yaw turned out not to be shifted horizontally with respect to the rotor axis. 8 refs.

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