ANALYSIS OF A COUNTER ROTATING VERTICAL AXIS WIND TURBINE

This study analyses the performance of a counter rotating vertical axis wind turbine (CRVAWT). The CRVAWT consists of two separate three-blade rotors where conducting coils were fixed onto one turbine and permanent magnets were attached to the other turbine. Both rotors rotate in the opposite direction which, according to Faraday’s law of electromagnetic induction, significantly increases the performance of the device. A H-Darrieus type turbine was chosen for the analysis due to its higher efficiency. Both turbines were made to rotate in a counter-rotating motion by orientating their airfoil blades in the opposite direction. The device was fabricated, assembled and tested in a low-speed wind tunnel. Experimental results show that the CRVAWT obtained a much larger power output of up to five times that of the conventional VAWT (CVAWT). However, the coil-attached turbine displayed a lower rotational speed than the magnet-attached turbine due to resistance from the slip ring. This also caused the cut-in wind speed for the former turbine to be higher than the latter one. Additionally, while the coefficient of power for the CRVAWT is identical to the CVAWT, the efficiencies for both rotors vary differently with wind speed due to the slip ring. Nevertheless, the CRVAWT demonstrated a higher overall efficiency at wind speeds larger than 8.0 m/s and similarly, the power density of the CRVAWT becomes significantly larger than the CVAWT at wind speeds above 8.0 m/s.