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https://doi.org/10.5194/wes-2018-46
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Research articles 18 Jul 2018

Research articles | 18 Jul 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Wind Energy Science (WES).

Aerodynamic characterization of a soft kite by in situ flow measurement

Johannes Oehler and Roland Schmehl Johannes Oehler and Roland Schmehl
  • Faculty of Aerospace Engineering, Delft University of Technology, 2629 HS Delft, Netherlands

Abstract. Wind tunnel testing of large deformable soft kites for wind energy conversion is practically not feasible. Computational simulation of the coupled fluid-structure interaction problem is scientifically challenging and of limited practical use for aerodynamic characterization. In this paper we present a novel experimental method for aerodynamic characterization of flexible membrane kites by in situ measurement of the relative flow, while performing complex flight maneuvers. We find that the measured aerodynamic coefficients agree well with the values that are currently used for flight simulation of soft kites. For flight operation in crosswind maneuvers where the traction force is kept constant, the angle of attack and the apparent flow velocity exhibit opposite trends. For entire pumping cycles, the measurements show considerable variations of the aerodynamic coefficients, while the angle of attack of the kite varies in fact only in a narrow range. This finding questions the commonly used representation of aerodynamic coefficients as sole functions of the angle of attack and stresses the importance of aeroelastic deformation for this type of wing. Considering the effect of the power setting (identical to the trim) solely as a rigid-body pitch rotation does not adequately describe the aero-structural behavior of the kite. We show that the aerodynamic coefficients vary as functions of the power setting (trim) of the kite, the steering commands and flight direction.

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Johannes Oehler and Roland Schmehl
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Johannes Oehler and Roland Schmehl
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Short summary
The work describes a performance study on a deformable membrane kite that is employed for wind energy conversion (airborne wind energy). We use self-built wind vanes and a Pitot tube to sense the airflow at the kite which is a new approach for leading edge inflatable kites that are mainly used for kite surfing. Actively controlled as well as unplanned deformations of the airfoil have a (negative) effect on the aerodynamic performance of the kite, turning maneuvers also decrease the performance.
The work describes a performance study on a deformable membrane kite that is employed for wind...
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