Ram air kite tethered to an adjustable handle bar in the wind tunnel of Cranfield University
Alex Rementeria Zalduegui MSc Student Cranfield University School of Aerospace, Transport
and Manufacturing SF497 College Road Bedford MK43 0FW United Kingdom al.rementeria@gmail.com www.cranfield.ac.uk/centres/centre-for-aeronautics
Wind Tunnel Parametric Study of Kite Performance for Power Generation
Alex Rementeria Zalduegui, Kevin Garry Cranfield University
High deformability, high anhedral and low aspect ratio are some of the features that make ram-air kites differ from conventional wings. With the emergence of Air-borne Wind Energy technology, it is considered necessary to increase the volume of available data on kite aerody-namics as they are key to a proper technology optimisa-tion. Wind tunnel tests of all-flexible kites are rare be-cause of the practical difficulties in data extrapolation to full-scale, atmospheric flight. However, they are still use-ful for parametric studies in a more controlled environ-ment.
As a result, wind tunnel tests of a scaled, four-line ram-air kite have been undertaken at Cranfield University. The kite was tethered upside down to a manually adjustable handle bar, which was used to introduce the two main input parameters: handle spanwise spacing and handle pitch angle. The first affects wing anhedral, and the latter is proportional to the amount of pull of brakes and kite attitude.
Tests were carried out over a range of wind speeds for every configuration of wing anhedral and handle pitch angle. A limitation of the tests has been the lat-eral/directional stability of the kite. The problem was overcome by applying a minimum pull of brakes at every test, which in turn had an impact on the fidelity of exper-iments.
As for the parametric study, wing anhedral leads to a de-crease of both CLand CD. The effect of increasing the
pull of brakes is that of reducing L/D, a sign of the effec-tiveness of the device. CLand CDhave been seen to be
Reynolds number dependent, both converging with dy-namic pressure. Maximum L/D values above 4 have been obtained with the highest wing anhedral and the smallest pull of brakes. 0 10 20 30 40 50 60 0 5 10 15 20 25 30 Drag (D) [N] θ = 0 deg θ = 5 deg θ = 10 deg θ = 15 deg θ = 20 deg Pull of Brakes L/D = 2 L/D = 5 Li � (L) [N]
Lift vs Drag polar; θ = handle pitch angle ∝ pull of brakes. The project is considered valuable as a preliminary study of the impact of wind speed, wing anhedral and pull of breaks on kite performance. Further work will focus on kite stability and an advanced imaging setup, as well as alternative experimental approaches.
References:
[1] de Wachter, A.: Deformation and aerodynamic performance of a ram-air wing. MSc Thesis. Delft University of Technology (2008) [2] Nicolaides, John D.: Parafoil Wind Tunnel Tests. AFFDL (1971)
