THEORETICAL AND EXPERIMENTAL STUDY OF VERTICAL AXIS KOBOLD TURBINES HYDRODYNAMICS

This technical report describes the activity performed by INSEAN, The Italian Ship Model Basin, to study hydrodynamics aspects of a mechanical device known as "Kobold turbine." This activity is performed in the framework of Contract No. 01CS06 between INSEAN and Ponte di Archimede S.p.A. The term Kobold is used here to denote a vertical-axis multi-bladed rotor that is fully submerged and subject to an incoming flow. Rotor blades have a rectangular untwisted shape and are partially free to oscillate about a spanwise hinge axis. Each blade is linked to the rotor shaft by one or more arms. The hydrodynamic force acted by water on the blades generates a torque that puts the blades, and hence the rotor, in rotation about its shaft. Basic objective of the present research program is to investigate hydrodynamics aspects affecting Kobold turbine performance, i.e., its capability to extract kinematic energy of sea currents and to convert it into mechanical energy. To this purpose, theoretical models and computational tools are developed to predict the torque generated by turbine blades of given shape and dimensions and subject to an incoming current of prescribed intensity. In addition, experimental activity is conducted on a turbine model to characterize the hydrodynamic behaviour of the device and to provide data for the assessment of the aforementioned computational prediction tools.