# Fluid Flow-Based Vibration Energy Harvesters: A Critical Review of State-of-the-Art Technologies
## 8 Rotary Wind Energy Harvesters  
A rotary wind energy harvester (RWEH) is a device that converts wind energy into mechanical energy (rotating motion) and then into electrical energy. This technology is commonly used to extract wind energy with rotating rotors, like wheels, turntables and turbines. Scholars have performed extensive research on RWEHs due to their significant potential for environmental monitoring. Due to randomness of environmental wind energy sources, the use of RWEHs for self-powered sensing has become a viable and realistic solution in the context of environmental condition sensing and monitoring [205]. The challenge in designing such RWEHs is to enhance energy gathering efficiency over a large wind-speed range and in multiple directions. Figure 14a illustrates a rotational PEH presented by [PERSON] et al. [206]. The blowing wind causes the fan blade and turntable to rotate. The turntable impacts the PVDF beam, causing it to vibrate. The harvester can efficiently scavenge wind energy. At a 14 m/s wind speed, the RMS voltage of 160.2 V with a maximum output power of 2566.4 \(\mu\)W was achieved. [PERSON] et al. [207] suggested a hybrid RWEH that can be used to capture wind energy. The device mechanism comprises a spinning body and a sliding body, as shown in Figure 14b. The complete power production system is composed of TEEHs on the sliding body and an EMEH in the rotating body. The voltages of the TEEH and the EMEH are 416 V and 63.2 V, respectively, at the wind speed of 15 m/s. The output performance of TEEHs and EMEHs rises with increasing wind speed. The highest output powers of the TEEH and EMEH are 0.36 mW and 18.6 mW, respectively, at a wind speed of 9 m/s. [PERSON] et al. [208] reported a hybrid RWEH that combined a rotating EM component with a soft friction and positive-directional TEEH. The distinctive design overcomes the oscillating output of traditional TEEHs and enables consistent, positive energy output. The layered design of the harvester maximizes the use of wind energy for greater output. This configuration enables IoT sensor nodes to monitor the forest environment, enabling the wireless collection and transmission of temperature and humidity data, ultimately assisting in the prevention of forest fires. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Coupled** & **Shape of the** & **Cut-in Velocity** & **Optimum** & **Velocity at Max** & **Output Power** & **References** \\
**Mechanism** & **Bluff Body** & **(m/s)** & **Resistance** & **Power (m/s)** & **(mW)** & **References** \\ \hline VIV-Galloping & Diamond- & & & 200 & 32 & - & [PERSON] et al. [46] \\  & shaped baffle & & & 50 & 2.95 & - & [PERSON] et al. [77] \\ \hline \begin{tabular}{c} Galloping- \\ Wake galloping \\ \end{tabular} & D-shaped & 2.45 & 410 & 9 & 2.3 & [PERSON] et al. [147] \\ \hline VIV-Galloping & T-shaped & \(<\)2 & 1500 & 3 & 0.4 & [PERSON] et al. [195] \\ \hline VIV-Galloping & Fin-shaped & & & 200 & 6.8 & 1.645 & [PERSON] et al. [199] \\ \hline VIV–Wake & \begin{tabular}{c} Cylindrical- \\ shaped \\ \end{tabular} & \begin{tabular}{c} (i) \\ (ii) \\ \end{tabular} & 0.8 & \begin{tabular}{c} (i) \\ 2.5 \\ \end{tabular} & \begin{tabular}{c} 1000 \\ 250 \\ \end{tabular} & 6.5 & 0.00875 & [PERSON] et al. [201] \\ \hline VIV–Galloping & \begin{tabular}{c} Rectangular \\ with leeward \\ protrusion \\ \end{tabular} & 2 & 200 & 5.1 & 0.992 & [PERSON] et al. [200] \\ \hline \begin{tabular}{c} Flutter–VIV \\ (ii) \\ \end{tabular} & \begin{tabular}{c} Airfoil \\ Cylinder \\ \end{tabular} & 5.42 & 400 & 14.48 & 0.154 & [PERSON] et al. [202] \\ \hline \
\begin{tabular}{c} Cylindrical \\ with two \\ airfoils \\ \end{tabular} & 4.8 & 140 & 9 & 6.47 & [PERSON] et al. [203] \\ \hline
\begin{tabular}{c} Flutter–VIV \\ \end{tabular} & Airfoil & 7.6 & 250 & 14.39 & 5.43 & [PERSON] et al. [204] \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Energy harvested based on multiple FIV phenomena. Figure 14c [209] depicts a hybrid RWEH, which employs PE, EM and TE mechanisms.