Background: Medium and small-scale wind turbines with no pitch control are cheaper than their controlled equivalents but are much more affected by aerodynamic stall, and local boundary layer separation occurs on the blade when critical wind speed is exceeded. As a result, they produce relatively low power. In this study, the delay of separation of the boundary layer from the surface was investigated by increasing the kinetic energy of the low-momentum fluid behind the surface utilizing the airflow from the air ducts added on the blade.
Methods: To obtain the optimum performance from the blade, a computer-aided optimization study was conducted by taking the slope, diameter, number, and angle of attack parameters of the air ducts. The response surface methodology, a goal-oriented and multi-purpose method, was used as an optimization method to provide the best possible design according to the constraints and targets set for the parameters.
Results: Optimum parameter values were determined using computational fluid dynamics analysis, and air ducted blade design was compared with the air duct-free blade design, and as a result, the power coefficient obtained from the blade was improved between 3.4% and 4.4% depending on wind speed.
Conclusions: Opening air ducts up to a critical number of ducts increase viscous forces. this provides more power from the rotor. On the other hand, with the extra airflow coming from the air ducts, the flow separation behind the wing is delayed and the stall effect is shifted to higher wind speeds and the rotor can work for a longer time at nominal power. Besides, since all this is done with passive flow control, a remarkable increase in annual electricity production from the turbine is provided.