SLATTED-BLADE SAVONIUS WIND-ROTORS

The Savonius rotor can develop a relatively high torque at low rotational speeds and is cheap to build, but it harnesses only a small fraction of the wind energy incident upon it. One initially attractive proposal for augmenting its harnessing effectiveness, was to fit an array of hinged flaps in place of the curved parts of the turbine's blades. The flaps open automatically as a result of wind pressure when they advance into the wind (and hence experience less flow-resistance), but close (again automatically) when retreating from the wind, i.e. during the power-harnessing part of the cycle. It had been found previously that this arrangement, as required, significantly enhances the static torque imposed by the wind on the rotor. So, in this study, dynamic-torque and power-harnessing tests were carried out for a Savonius rotor as well as for rotors modified with 8 or subsequently 16 hinged flaps. The modified rotors displayed slightly increased torques at low rotational speeds, but the traditional Savonius rotor developed a peak power-coefficient of 18% compared with only 5% for the slatted turbines.