Enhanced energy extraction in small-scale wind turbines through slot-based passive blowing

The increasing demand for sustainable energy has spurred research and development of wind turbines. In this study,
a passive flow-control technique using a non-uniform curved slot is proposed. The slot is engraved on the midchord region of the National Renewable Energy Laboratory (NREL) Phase VI wind turbine blade, between the
quarter-span and tip radial stations. The impact of slot-induced flow control is investigated using three-dimensional
transient computational fluid dynamics (CFD) modeling across a range of wind speeds, including pre-stall and deepstall conditions. Aerodynamic analyses are performed to ascertain the influence of slot-flow on the complex threedimensional flow dynamics around the blade. The slotted blade demonstrates significant improvements in lowspeed shaft torque and power compared to the baseline blade. Additionally, the slotted blade experiences increment
in the inherent thrust and flapwise bending moments. Detailed wake flow field and surface flow visualization
indicate that the slot promotes a more streamlined attached flow across the blade span, delaying flow transition and
suppressing turbulence on the blade surface and downstream wake. The slot-flow also reduces radial flow and tipvorticity anomalies along the blade. Overall, flow control enhancement achieved by the slotted blade significantly
boosts the annual energy production of the wind turbine.