Improvement of the power extraction performance of a semi-active flapping airfoil by employing two-sided symmetric slot airfoil

Highlights: • The influence of two-sided symmetric slots on the FAPG were investigated. • The efficiency was increased 6.01% for the generator with optimized slot airfoil. • The effect lift was increased due to the reducing mass by the slot. Low power extraction efficiency is considered as one of the significant drawbacks of the semi-active flapping airfoil power generator (FAPG). A novel two-sided symmetric slot airfoil was employed in this work to overcome this problem. A coupled numerical method was developed and validated to simulate the interaction between the wind and flapping airfoil. Moreover, the TAGUCHI method was employed to select candidate parameters of the slot and arrange the virtual design of the numerical experiment. It is shown that the power extraction performance of the semi-active FAPG can be improved by employed slot airfoil, compared to the generator with baseline elliptical airfoil, the maximum efficiency is increased 6.01% for the generator with optimized slot airfoil. The aerodynamic behavior analysis of the airfoil showed that due to the slot, the effect lift of the airfoil is increased, therefore improves the passive rotation velocity and power extraction performance of the FAPG.