# Fluid Flow-Based Vibration Energy Harvesters: A Critical Review of State-of-the-Art Technologies
## 4 Galloping Energy Harvesting
### Galloping PE-FBEHs  
[PERSON] and [PERSON] [66; 67] devised a variety of galloping energy harvesters with cantilevers and attached prisms with triangular and D-shaped cross-sections. The impacts of the cross-section geometry of the bluff body on the onset speed of galloping-based piezoelectric energy harvesters (PEHs) were studied theoretically and experimentally by [PERSON] et al. [68] and [PERSON] et al. [69]. It was demonstrated that energy harvesters with square-shaped cross-sections operate most effectively. Consequently, many researchers developed energy harvesting systems with improved and unique-shaped bluff bodies [70; 71]. [PERSON] et al. [72; 73] investigated the installation of rods or fins along the edges of bluff bodies as an aerodynamic modification approach to enhance aerodynamic performance. [PERSON] et al. [74; 75] constructed a Y-shaped bluff body and a fork-shaped bluff body (Figure 6c). [PERSON] et al. [76] discovered that the Y-shaped galloping energy harvester performs significantly better than the square-shaped galloping energy harvester. Recently, [PERSON] et al. [77] devised a bulb-like cross-sectional (Figure 6b) bluff body to achieve higher efficiency over a broad operational wind velocity range. To improve the efficiency of a PE-FBEH, [PERSON] et al. [78] presented a curved-plate bluff body and compared it to bluff bodies with standard cross-sections (square, regular-triangle and D-shaped cross-sections). According to their experimental findings, a curved-plate bluff body with a particular arc length can produce a larger output voltage and a lower cut-in wind velocity. A similar approach of the curved-tip body of a galloping energy harvester was presented by [PERSON] et al. [79]. Better aerodynamic efficiency is made possible by the blade shape, which is curved, resembling an airfoil rather than a bluff body. [PERSON] et al. [80] attached a rigid splitter structure to the end of a square bluff body. The results indicated a 67% increase in the output power. [PERSON] et al. [81] used a square prism galloping energy harvester surrounded by an enclosure which experiences an increase in aerodynamic force as a result of the movement of the bluff body in relation to the enclosure. [PERSON] et al. [82] introduced a square cylinder with a V-shaped groove on the windward side that can change both the lateral force on it and the critical velocity (ranging from 2.53 to 4.69 m/s). This approach enhanced the output power by 61%. A similar approach in [83] was also focused on the galloping energy harvester's performance by analyzing the effects of different V-groove depths on the bluff body. The harvester produces its highest output power in environments with low wind speeds. [PERSON] et al. [84] developed a cut-corner prism type PE-FBEH based on a galloping enhancement mechanism, as illustrated in Figure 6d. An innovative, galloping energy harvester in the shape of a funnel was presented by [PERSON] et al. [85]. It has a high normalized harvesting power and a broad working wind-speed range. The structural non-streamline fluid flow is improved by this topological aerodynamic design, and the pressure direction is made to follow the lift-force direction, increasing the aerodynamic force, and improving the efficiency of the energy harvester. [PERSON] et al. [86] developed a novel FIVs energy harvester based on a corrugated-shaped bluff body as illustrated in Figure 6e, which was tested at low wind speeds resulting in a 189% increase in response to a 2 m/s wind speed. In [87], the PE-FBEH utilizing a double bluff body exciter provided great reliability, the ability to generate power at low wind speeds and adaptability to varying wind conditions. Another approach reported by [PERSON] et al. [88] investigated the durability and adaptability of a PEH in variable wind conditions. A double-airfoil-structured bluff body (Figure 6f) with adjustable attack angles is suggested to exploit the advantages of various types of FIVs based on the local wind speed.