Start-up Dynamics of Vertical Axis Wind Turbines: A Review

Vertical Axis Wind Turbines (VAWTs) are becoming increasingly popular for wind power extraction due to their simpler design, lower manufacturing and maintenance costs. The omni-directionality of these power generating machines make them more suitable for operation both under lower wind speeds and highly transient winds. The key wind power extraction component of VAWTs is their rotor, which is conventionally either Drag-based or Lift-based, with the latter being more widely studied in the published literature due to its higher power coefficient compared to its counterpart. The lift-based rotor comprises of aerodynamically profiled blades, while the drag-based rotor comprises of thin cup-shaped blades. The start-up of both these types of VAWT rotors has been an area of active research in the last decade. These studies have been conducted using numerical and experimental methods focusing on key parameters related to the start-up dynamics of VAWTs. Many of these research studies complement each other's findings, however, there are also a number of aspects where there are disagreements and/or significant knowledge gaps that need to be highlighted in order to accelerate scientific efforts strategically. In the present study, we aim to address these challenges through a thorough and critical review of the published literature on VAWTs' start-up dynamics, leading towards the identification of key knowledge gaps.