Automatic Measurement and Characterization of the Dynamic Properties of Tethered Flexible Wings

Towing test bench of TU Berlin in operation at former airfield Pütnitz, Germany (19 May 2016)

Jan Hummel Postdoctoral Researcher Technische Universität Berlin

Department of Methods for Product Development and Mechatronics

Straße des 17. Juni 135 10623 Berlin

Germany

jan.hummel@tu-berlin.de www.mpm.tu-berlin.de

Automatic Measurement and Characterization

of the Dynamic Properties of Tethered Flexible Wings

Jan Hummel, Dietmar Göhlich Technische Universität Berlin

Despite the lack of reproducible measurements, the de-sign and de-significance of flexible tethered airfoils has in-creased considerably. While existing design methods have proven useful in achieving a high degree of maturity on product level, this has primarily been accomplished by the empirical variation of wing parameters. Measure-ments under reproducible conditions, including repro-ducible steering inputs, have not been carried out yet. To address this lack of measurements, we established the project TETA within a doctoral research project. A test bench was developed that allows for accurate testing of different types of tethered airfoils. The test bench can be used stationary or by moving at a specific velocity to sim-ulate different wind speeds as well as reducing influences by gusts.

The test bench focuses on the constant airflow genera-tion, the measurement of the entire kite system under realistic conditions and the possibility to initiate repeat-able, automated maneuvers.

The findings described in this thesis enable an objec-tive measurement of specific dynamic wing properties of highly flexible tethered airfoils (e.g. aerodynamic coeffi-cients and forces). In the scope of this work, airfoil prop-erties, which are defined as dynamic, are determined against variable control inputs or kite positions. The dynamic properties are successfully determined by using the žLinear Powerž maneuver. Hereby, the ratio be-tween front lines and control lines (εrel) is automatically varied within a predefined length (see figure).

A brief overview of the experimental procedure as well as exemplary results are given, including a short description of the data processing.

The measurement results are essential for the develop-ment and characterization of these airfoils as well as for the validation and improvement of simulation models. Furthermore, it demonstrates that the method is suit-able for comparing basic airfoil design concepts. The thesis makes a decisive contribution to the evaluation of follow-up designs and simulation models of highly flexi-ble tethered airfoils.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 εrel 0 0.1 0.2 0.3 0.4 0.5 0.6 f Kite Size [m2 ] Maneuver 14 14 14 10 126 85 82 288 Genetrix Hydra V5 North Evo 2014 North Rebel 2016 North Vegas 2015 [-] [-]

Exemplary measurement curve: force ratio between back and front linesf = (FSL,l+ FSL,r)/FPLagainst power ratio εrel(P=95%).