Effect of blade attachments on the performance of an asymmetric blade H-Darrieus turbine at low wind speed

Wind energy is a significant source of renewable energy and vertical axis wind turbine (VAWT) is one of the advanced wind energy harvesters. Maximum extraction of energy from wind harvesters is a major goal. Researchers are faced with the challenge of enhancing the performance of VAWTs in low wind speed conditions. To this end, researchers have contributed substantially by doing research on the blade design parameters thereby generating innovative and improved VAWT designs. However, there is hardly any work on the performance augmentation of H-Darrieus VAWT with blade attachments on asymmetric blades, which is the main objective of this work. Further, this work investigates the combined effect of turbulence intensity and flow dissimilarity on turbine performance for low wind speed condition. In this paper, blade attachment of length 20 cm (equal to 1/2.5 times blade span) is attached to asymmetric NACA 63-415 blade turbine having fixed blade pitch angle (+5 degrees). NACA 63-415 blade profile is one of the prominent asymmetric series of NACA blades; hence it is considered in this work. The performances of seven different configurations of the turbine with blade attachments have been investigated experimentally at 5.0 m/s and 6.0 m/s using wind tunnel testing. The performance of the VAWT design is systematically improved by changing the number and position of these attachments on the turbine blades. The result shows that both side attachments on turbine blade on its top position have maximum power coefficient (C-p) of 0.13 at tip speed ratio (TSR) 1.8 at wind speed 6.0 m/s among all the turbine configurations tested. There is an improvement of power coefficient by 4.34% when attachments are placed at top of the turbine blade compared to turbine blade without attachment at wind speed 6.0 m/s. Further, maximum power coefficient is increased by 3.28% when turbine is operated from 5.0 m/s to 6.0 m/s for both side attachments at top of the turbine blade. Moreover, due to the combined effect of turbulence intensity and flow dissimilarity, the power coefficient of the turbine configuration having both side attachments has also improved a little. In this case, an improvement of 0.6% in power coefficient of turbine having both side attachments on top of the blade is achieved. As the turbine is a prototype having smaller size hence the effect of turbulence intensity and flow dissimilarity is less, in case of actual turbine of bigger size the effect of turbulence intensity and flow dissimilarity will be more and hence the percentage enhancement of power coefficient will also be more. Hence, it can be concluded that a turbine blade with higher degree of thickness (by using blade attachments) at top portion will increase the performance of an asymmetric blade H-Darrieus VAWT.