A fully-enclosed torsional galloping electromagnetic wind energy harvester

Most galloping wind energy harvesters (WEHs) are based on transverse galloping, whereas very few utilize torsional galloping. Adopting a fully-enclosed structure to protect components vulnerable to harsh external environmental conditions can improve the stability and reliability of WEHs. The existing fully-enclosed WEHs need two spring-mass systems, and the frequency mismatch between them reduces the stability of electrical output. This paper proposes a fully-enclosed torsional galloping electromagnetic wind energy harvester (TGEWEH) with the torsion movement caused by the aerodynamic torque on bluff body. It only has one spring-mass system and does not involve frequency matching, thus potentially improving the stability. Based on the quasi-steady assumption, a mathematical model of TGEWEH is presented. Experiments show that sealing the bluff body shell’s opening with a flexible film has an acceptable impact on the cut-in wind speed and electrical outputs. The simulated voltages agree well with the experiments, indicating that the proposed model meets the requirement of TGEWEH design. The harvester with the bluff body side ratio of 1.5 achieves the maximum output power of 4.41 mW and power density of 36 μW/cm 3 at 15 m/s, which are higher than existing torsional galloping WEHs and semi- or fully-enclosed WEHs. It can stably drive a wireless sensor node in the wind speed range from 4.14 to 15 m/s. For the improved stability of fully-enclosed WEHs with one spring-mass system, and the high power density and wide wind speed range of torsional galloping WEHs, more relevant research is worth conducting in the future.