Experimental Study to Assess the Performance of Combined Savonius Darrieus Vertical Axis Wind Turbine at Different Arrangements

Darrieus Vertical axis wind turbines (VAWT) have become one of the most worked on turbines in the 20th century, due to the various improvement regimes been carried out to improve their performance, especially the H-shaped Darrieus wind turbines. The Darrieus wind turbines are considered more aerodynamically efficient than the rest of VAWT, however they have been highly undesirable in areas with low wind velocities since these turbines have poor starting torque and are hence unable to self-start in weaker wind speeds. Combined Savonius Darrieus wind turbines have been pitched as the solution for improving turbine's torque characteristics and enable it to self-start. In this study, an experimentation has been carried out to test three possible arrangements of Darrieus and Savonius wind turbine; termed as arrangement 1, 2 & 3, under similar operating conditions to assess performance of each arrangement. It was observed from the arrangement 1; where Savonius rotor was attached at the middle of Darrieus wind turbine, had the highest coefficient of performance among all arrangements, achieving maximum COP of 20% at TSR of 0.86. Arrangement 2 and 3; Savonius rotor attached at the top of Darrieus rotor and Savonius attached at the bottom of Darrieus turbine had significantly lower COP than arrangement 1 - having COP of 10% at 0.56 TSR and 5% at 0.28 TSR, respectively. Henceforth, arrangement 1 is recommended if turbines are to be combined.