Theory and practice of a horizontal-axis flexible sail type wind-turbine behaviour.

A sail of 0.3m x 0.28m, with 1% slack, was placed in the test section of a wind tunnel. Both surface visualization and pressure distribution tests were undertaken with the sail at various angles of attack, oc , relative to the wind, for a constant wind speed of 5 m/s. As O the angle of incidence was increased from 2.5 , it was found that the flow round the sail behaved in a smooth manner until oc reached 15° . Beyond 15° , flow separation became dominant and for higher angles of attack (i.e. oc >25°) the sail flapped violently. It was also found that the lift increased linearly with oc and the sail stalled at an angle of incidence of oc =15° . At zero angle of attack the lift was found to be negative. The performance of a fully-augmented flexible sail-type wind turbine has been investigated. The augmentation devices (i.e. centre-body and tip-fins) used resulted in an increase of about 60% over the unaugmented wind turbine. Tests were carried out so as to determine the pumping characteristics of the wind turbine when it was coupled to a commercially-available peristaltic pump. Aerodynamic characteristics of the interacting sails, together with the effectivenesses of the above mentioned augmenting devices, were investigated using a flow-visualization technique and this was done at the optimal operating wind-speed of 5 m/s. Tests on the wind-turbine/pump combination show that the cut-in and cut-out wind speeds for the pump to function were 3.71 and 11 m/s respectively.