Wind tunnel testing of a wind turbine with telescopic blades: The influence of blade extension

In this paper, the aerodynamic performance of the telescopic blade wind turbine concept has been analysed experimentally and computationally. A model-scale wind turbine with two-stage telescopic blades, having a chord ratio of 0.6, was studied in the wind tunnel for different blade extensions (i.e. different lengths of the second section, ranging 0–40% of the first section). The experimental setup allowed the measurement of rotor speed, shaft torque, and thrust, under varying wind speeds. It has been established that the effect of a step change in blade chord is significant for the range of blade extensions studied. In particular, the power coefficient Cp of the wind turbine was found to decrease with extension, with 25% decrease in maximum Cp obtained for a 20% blade extension. This is attributed to additional losses arising from the step change in chord. Correlations proposed to quantify losses arising from the step change in the chord of a telescopic blade are found to be in good agreement with experimental data. In spite of the detrimental effects of a step change in blade chord, the power output of a telescopic blade wind turbine is found to increase for all blade extensions considered in this study.