Passively adaptive wind energy harvester featuring a double-airfoil bluff body with adjustable attack angles

•A passively adaptive wind energy harvester is proposed in a mode-switching way.•Three typical working modes are realized by adopting the double-airfoil bluff body.•An aero-electromechanical model is developed and verified for the proposed harvester.•Positive aerodynamic work and dynamic stall are beneficial for energy harvesting.•The proposed harvester is superior to the conventional galloping-based one.