A review of augmentation methods to enhance the performance of vertical axis wind turbine

• Augmentation devices increase wind velocity at inlet due to venturi effect. • Self-starting ability improved for both lift and drag type VAWTs. • INVELOX, cowling, shroud significantly increase rotational speed of turbine. • Augmentation can be achieved by modifying blade geometry without any extra devices. Vertical axis wind turbines (VAWTs) are advantageous than horizontal axis wind turbines (HAWTs) in terms of portability and ease of application in urban areas and turbulent environments. Though VAWTs have lower efficiency than HAWTs in ideal low-turbulence wind environments, in high-turbulence and directionally shifting wind circumstances, VAWTs function more smoothly and produce higher energy than HAWTs. However, their low efficiency, self-starting capabilities and inability to generate continuous positive torque are the main downsides. To harness maximum energy from flowing streams, augmentation techniques can be deployed for VAWTs, which is the subject of the present work. The methods that are tried include modification of inlet flow path, modification in blade profiles and several other innovative designs such as cowling technique and INVELOX profile. These new design methods are mainly focused on reducing negative torque and increasing the inlet velocity of the wind. Research has shown that there is a substantial increase in the power coefficient ( C P ) and the output power of different VAWTs by incorporating augmentation systems.