Methodology Improvement for Performance Assessment of Pumping Kite Power Wing

Abstract

Pumping kite power systems are a promising way of harnessing clean energy from high-altitude winds. A large kite flies crosswind developing a strong pulling force through a tether which is connected at the ground to an electrical generator. The power output of such innovative systems is directly related to the wing aerodynamic properties which therefore play a key role. Moreover, the latter, often assumed with best guess, are also required for computational simulations at development stage. In this context, the research group of TU Berlin recently designed a car towing test bench for evaluating flexible airfoil performances in an automated and repeatable manner. By towing the kite at a prescribed speed, relevant information, such as tether force and elevation angle, are extracted and can be converted into aerodynamic properties thanks to a suitable analytical model. With the purpose of improving the assessment of aerodynamic properties and their exactitude, the present work takes advantage of the TU Berlin test bench by investigating the Kitepower wing. An alternative testing methodology is suggested and compared against the current procedure, indicating a dynamic behaviour of the kite. A 2D quasi-steady point mass model is implemented to compute the kite aerodynamic properties by taking both wing and tether mass as well as tether aerodynamic effects into consideration. Eventually, a detailed analytical model of the tether is developed to assess its sag and effects on the kite performance. Finally, an attempt to provide polar curves with re-spect to the angle of attack rather than the power ratio is experimentally carried out.