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The state-of-the-art review on energy harvesting from flow-induced vibrations

Citation for published version:Wang, J, Geng, L, Ding, L, Zhu, H & Yurchenko, D 2020, 'The state-of-the-art review on energy harvestingfrom flow-induced vibrations', Applied Energy, vol. 267, 114902.https://doi.org/10.1016/j.apenergy.2020.114902

Digital Object Identifier (DOI):10.1016/j.apenergy.2020.114902

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Download date: 02. May. 2022

The state-of-the-art review on energy harvesting of flow-induced 1 vibrations 2 3 Junlei Wanga, Linfeng Genga, Lin Dingb,*, Hongjun Zhuc,* and Daniil Yurchenkod 4 a School of Mechanical and Power Engineering, Zhengzhou University, Zhengzhou, China 5 b School of Power Engineering, Chongqing University, Chongqing, China 6 c State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum 7 University, Chengdu, Sichuan 610500, China 8 d Institute of Mechanical, Process & Energy Engineering, Heriot-Watt University, Edinburgh 9 EH14 4AS, UK 10 E-mail: linding@cqu.edu.cn; zhuhj@swpu.edu.cn 11

Abstract 12 In this paper, the current popular flow-induced vibrations energy harvesting 13

technologies are reviewed, including numerical and experimental endeavors, 14 and some existing or proposed energy capture concepts and devices are 15 discussed. The energy harvesting mechanism and current research progress of 16 four types of flow-induced vibrations, such as vortex-induced vibrations, 17 galloping, flutter and buffeting, are introduced. To enhance the performance of 18 the harvesters and broaden the operating range, the researchers have proposed 19 various mechanical designs, methods of the structures’ surfaces optimization 20 and incorporated magnets for multistability. The paper summarizes the works 21 led to current wind energy and hydro energy harvesters based on the principle 22 of flow-induced vibrations, including bladeless generator Vortex Bladeless, 23 University of Michigan vortex-induced vibrations aquatic clean energy 24 (VIVACE), Australian BPS company's airfoil tidal energy capture device 25 bioSTREAM, and others showing the gradual progress and maturity of the 26 flow-induced vibrations energy harvesters. The article concludes with a 27 discussion on the current problems in the area of flow-induced vibration 28 energy capture and the challenges the area faces. 29

Keywords: Flow-induced vibration; Energy harvester; Hydrokinetic energy; Wind 30

energy 31

Introduction 32

In recent years, the burning of oil, coal and other fossil fuels has caused 33 increasingly serious environmental problems, and fossil energy is increasingly 34 exhausted, thus the issue of harvesting clean and renewable energy from the 35 environment remains a critical research hotspot [1-3]. A flow-induced vibrations 36 (FIVs) energy harvester is a micro-environmental energy-capturing device designed 37 based on the principle of flow-induced vibrations. The device can harvest energy from 38 the surrounding flow field to supply energy to a micro-electro-mechanical system 39 (MEMS) and wireless sensing system to achieve continuous monitoring of the system 40 [4]. 41

FIVs is a very common physical phenomenon in engineering field that is caused by 42

aerodynamic instability or vortex shedding when fluid passes around a slender 43 structure [5]. Although FIVs may cause structural damage and huge economic losses, 44 it also has great potential for utilization, which can be used to harvest the hydraulic 45 energy, wind energy, and energy of flowing gas in HVAC. For example, the VIVACE 46 proposed by Bernitsas and Raghavan et al. [6], university of Michigan, converts tidal 47 energy into vibration energy by using the principle of vortex-induced vibrations 48 (VIVs), and then converts vibration energy into electrical energy through 49 electromagnetic induction device for harvesting. Compared with traditional hydraulic 50 generators, VIVACE has long service life, low maintenance cost and high energy 51 density. Vortex bladeless, a bladeless wind turbine developed by a Spanish company 52 [7], uses the principle of VIVs to harvest wind energy. The device has the advantages 53 of simple structure and low cost. In recent years, a large number of new FIVs energy 54 harvester have been proposed, so it is necessary to review the current FIVs energy 55 harvesting technologies and devices, which is helpful for researchers to understand 56 the latest research progress. 57

FIVs energy harvest involves three-field coupling of a flow, structure and electricity, 58 and this coupling is complex. In this paper, the basic mechanism of energy harvesting 59 of vortex-induced vibrations, galloping, flutter and buffeting as well as the relative 60 research directions at present are summarized firstly. Then, the common wind and 61 hydro energy harvest devices by flow-induced vibrations are introduces and possible 62 issues are discussed. Finally, the challenges of FIVs energy harvesting are debated. 63

1 Current Research Status of Flow-induced Vibration Energy 64 Harvesting 65 According to the different vibration mechanisms, the FIVs for energy harvesting 66 can be divided into four categories: VIVs, galloping, flutter and buffeting, as shown in 67 Fig. 1. The VIVs and buffeting belong to a family of forced response vibration. The 68 FIVs energy harvesters designed based on response vibration can operate normally at 69 low flow velocities, but the working bandwidth is limited by the natural frequency of 70 the structure, and they are mostly used for the low-speed flow energy harvesting. The 71 galloping and flutter belong to a family of limit-cycle vibration. Compared with the 72 previous family, the cut-in speed of in this group is higher, but its effective operating 73 speed range is wider, and larger response amplitude under higher wind speed can be 74 observed, which is beneficial for energy harvesting. This section discusses these four 75 kinds of common FIVs energy trapping devices. 76

77 Figure 1. Classification of Flow-induced vibrations [8]. 78

1.1 Vortex-induced vibrations 79

VIVs are closely related to a flow field velocity and bluff body structures [9]. When 80 fluid flows around the bluff body, the vortex occurs periodically in the wake behind 81 the bluff body. The shedding frequency f of the vortex is defined as f = uSt/L, where 82 the Strouhal number St is regarded as a constant within a certain Reynolds number 83 range (when 300 < Re < 1.5×105, St is 0.2) [10], u is the incoming flow velocity and L 84 is the characteristic length. The vortex shed behind the bluff body will generate an 85 asymmetric pressure field around it, then the bluff body will be subjected to 86 alternating aerodynamic forces, resulting in a finite amplitude of vibrations. With the 87 change of the incoming velocity, the frequency of vortex shedding varies. When the 88 vortex shedding frequency is close to the natural frequency of the bluff body, 89 resonance will occur and the bluff body will undergo a high amplitude vibration. At 90 the same time, the phenomenon of frequency lock-in may occur implying that within 91 a certain range of the incoming flow velocities, and the frequency of vortex shedding 92 will no longer change with the flow velocity. Facchinetti et al. [11] pointed out that 93 the structural oscillations equation and the wake oscillator model coupling can be 94 used to describe the vortex-induced vibrations. For a simple single-degree-of-freedom 95 (SDOF) piezoelectric energy capture model represented by a cantilever beam, an 96 electromechanical coupling term can be introduced on the basis of the vortex-induced 97 vibrations model of Facchinetti et al. [11] 98

(1) 99

(2) 100

(3) 101

In the above equations, (1) is the structural oscillations equation, Eq.(2) is the wake 102 oscillator equation, and (3) represents the circuit equation. Here η, and 103 represent the displacement, velocity, and acceleration of the oscillator respectively, ζ 104 represents a damping coefficient, ω is the natural frequency of the structure, ωshed is 105 the vortex shedding frequency, ρ0 and U0 represent the density and flow rate of the 106 incoming stream respectively, φ(Lb) is the end displacement of the cantilever beam. 107

and represent the drag and lift coefficients respectively, q represents wake 108

displacement. V, RL, Cp and θ are the circuit parameters. 109 The efficiency of the vortex-induced vibrations energy capture device is higher 110

when it works within the lock-in frequency region. When the incoming flow velocity 111 exceeds the corresponding velocity range, the vibrations will be out of tune, their 112 amplitude decreases sharply, as well as the efficiency of energy capture. Therefore, 113

( ) ( )

( ) ( )0

22

0 0 0

20 0 0

122 2

1 4 2

D b b

L b b

DC DU L L L V

DC DU L L L q

′+ + + + +

′= +

η ξω ρ ϕ ϕ η ω η θ

ρ ϕ ϕ

( ) ( )2 21 2shed shed b b

A Dq q q q L LD ′ + − + = +

λω ω ϕ ϕ η

0 PL

V C VR

+ − = θη

η η

DC0LC

the broadening the width of the lock-in frequency region becomes the focus of some 114 studies on the energy capture of VIVs. A classical structure of vortex-induced 115 vibrations energy capture device is based on a cylindrical bluff body, and researchers 116 have conducted a lot of work on the improvement of the structure. Azadeh-Ranjba et 117 al. [12] studied the influence of the aspect ratio of a rigid cylinder on VIVs, and the 118 results suggested that the increase of the length-width ratio of the finite length 119 cylinder can not only increase the response amplitude of the rigid cylinder, but also 120 broaden the lock-in frequency region of the VIVs. Alireza et al. [13] studied an effect 121 of a spring stiffness of a water energy capture device on VIVs under high Reynolds 122 numbers (1.5×104 ≤ Re ≤ 6×104). In the experiment, five springs of different stiffness 123 were selected within the range of 125 N/m < K < 495 N/m, and the system responses 124 under different stiffness were studied by changing the natural frequency of the system. 125 The experimental results suggested that the maximum amplitude and the lock-in 126 frequency region of the system are closely related to the spring stiffness, and the 127 increase of the natural frequency will result in the increase of the response amplitude 128 and widening the frequency range of the system. In addition, Wang et al. [14] 129 proposed a new S-E VIVPEH (Scanlan-Ehsan vortex induced vibrations piezoelectric 130 energy harvester) lumped parameter model. In that work, the authors argued that the 131 traditional semi-empirical mode (such as wake oscillator model, structural vibration 132 model, etc.) is not suitable for predicting the performance of the vortex-induced 133 vibrations energy harvester with a non-circular cross-section structure. The S-E 134 VIVPEH model use a decay to resonance experiment to identify the semi empirical 135 parameters. Compared with other semi-empirical models, the advantage of the model 136 is that there is no restriction on the cross-section structure of the bluff body in the VIV 137 calculation. In addition, the wake vortex distribution also has a great impact on the 138 VIV energy conversion efficiency [15-19]. Zhang et al. [15] proposed adding a fixed 139 cylindrical bluff body to the piezoelectric energy harvester of a cantilever beam 140 structure, as shown in Fig. 2. The cylinder is located in the wake region of the original 141 cylinder, and distance L between the two cylinders can be adjusted. The experimental 142 results are shown in Fig. 3. It can be seen that the bandwidth of the structure lock-in 143 frequency region is wider than that of the original device, and the bandwidth 144 decreases as the distance L increases. Song et al. [16] studied the performance of 145 adding a splitter plate at the end of a cylindrical vibrator for the vortex-induced 146 vibration energy harvester. The experimental device is presented in Fig. 4. The 147 experimental data shows that when the splitter plate exists, the working bandwidth of 148 the harvester increases gradually and the peak voltage decreases with the increase of 149 the normalized length LSP/D of the plate. When LSP/D is close to 0.5, the VIVs will 150 converge to a galloping motion, and thereafter the peak voltage increases as the wind 151 speed increases. When LSP/D is close to 1.0, the voltage curve will show a downward 152 branch, mainly due to the shear layer separation. 153

154 Figure 2. The schematic of the improved energy harvester [15]. 155

156 Figure 3. Performance of the energy harvester with the interference cylinder as a 157

function of the wind speed for different values of the spacing distance [15]. 158

159

Figure 4. Wind energy harvester with splitter plates on the circular in the wind tunnel 160 [16]. 161

In order to improve the efficiency of wind energy harvesting, Wang et al. [4] 162 investigated the influence of the Passive Turbulence Control (PTC) devices on the 163 VIVs energy harvester. In order to determine the optimal PTC structure in the 164 experiment, Wang et al. compared the energy harvester with different numbers and 165

sizes of PTC structure, as shown in Fig. 5. Fig. 6 shows the experimental results. It 166 should be noted that the PTC structure has a great influence on the working 167 bandwidth and output voltage of the energy harvester. Reasonable adjustment of the 168 rough belts structure can improve the performance of the vortex-induced vibration 169 energy harvester. VIVs also occur in bluff bodies of non-circular cross-section under 170 certain conditions [20-24]. Compared to the flow around the cylinder, when the fluid 171 passes the non-circular cross-section bluff body, the detached vortices are 172 asymmetrically distributed. The separation of the boundary layer of the square column 173 structure is different from that of a circular cylinder. Usually, the boundary layer 174 separation occurs at the leading edge angle, and the separation point is not changed 175 with the Reynolds number. Therefore, the influence of the attack angle is the focus of 176 some researches on the square-column vortex-induced vibrational energy harvesting 177 [20]. In addition, due to the aerodynamic instability of the square-column structure, 178 the galloping can occur at higher wind speeds. Compared with the single-mode VIVs, 179 the vortex-vibration-acceleration mode can significantly improve the working 180 efficiency [21]. 181

182 Figure 5. Experimental circular cylinder cross-section with different PTC structure 183

[4]. 184

185 Figure 6. Comparisons of energy harvesting efficiency between PTC cylinders with 186

smooth cylinder: bandwidth of lock-in and the peak value of voltage output [4]. 187 The current research on vortex-induced vibration energy harvesting can be divided 188

into the following streams: (1) vortex-induced vibration piezoelectric energy 189 harvesting with a nonlinear magnetic force [25-29]. The structure of a piezoelectric 190 energy capture device can be improved by introducing a magnetic field, and the 191

natural frequency of the structure can be reduced as well. By adjusting the natural 192 frequency of the structure, the device is capable of operating at low wind speeds. For 193 example, Zhang et al. [27] proposed to add a pair of mutually exclusive magnets to 194 the piezoelectric energy capture device of the cantilever beam structure, one is placed 195 at the bottom of the bluff body, and the other is placed at the bottom of the support, as 196 shown in Fig. 7. The experimental results suggest that the energy capture efficiency of 197 the device is improved by 29% and the lock-in frequency range is widened by 138% 198 when the nonlinear magnetic field force is applied, which obviously demonstrates the 199 positive effect. (2) Hybrid energy harvester based on VIVs [30-34]. The energy 200 harvesting efficiency of the device can be improved by using a combination of 201 electromagnetic, piezoelectric, electrostatic, and dielectric energy transduction 202 mechanisms. The structure of piezoelectric electromagnetic hybrid energy harvester 203 proposed by Zhao et al. [31] is shown in Fig. 8. The electromagnetic induction 204 element is added to the cantilever piezoelectric device creating a combination of 205 vibrational piezoelectric and electromagnetic power generation. The maximum output 206 power of this device can reach 16.55mW in the experiment tests, and the observed 207 power generation efficiency is higher than the single mode piezoelectric and 208 electromagnetic energy capture devices under the same operating conditions. (3) 209 Vortex-induced vibration energy capture device with a multi-degree-of-freedom 210 (MDOF) structure [35-40]. Compared with SDOF oscillators, the motion of MDOF 211 oscillators is more complex, but its practical application prospect is broader. 212 Guilherme et al. [35] constructed a two-degree-of-freedom (TDOF) vortex-induced 213 vibration piezoelectric energy harvesting model as shown in Fig. 9, where the rigid 214 cylindrical oscillator moves in both the cross-wise and in-line directions. The 215 authors established the electromechanical coupling equation for this model, and 216 studied the impact of the in-line to cross-wise natural frequencies ratio f* and the 217 parameter σ1 (σ1 is the correlation dimensionless quantity of the electromechanical 218 coupling coefficient of the system) on the system response and energy harvesting 219 efficiency. Subsequently, Guilherme and Lucas et al. [36] studied the influence of 220 degrees of freedom on the energy harvesting efficiency of the vortex-induced 221 vibrations capture energy device. The results suggest that the energy harvesting 222 efficiency of the TDOF system is significantly higher than that of the SDOF system 223 under various wind speeds due to the much higher amplitude of the cross-wise 224 oscillations of the TDOF. 225

226

Figure 7. The Schematic of piezoelectric energy capture device with a pair of 227 mutually exclusive magnets [27]. 228

229

230

Figure 8. Schematic of the energy harvester [31]. 231

232 Figure 9. Schematic representation [35]. 233

1.2 Galloping 234

Galloping is a typical phenomenon of self-excited vibrations caused by aeroelastic 235 instability, which occurs mostly in long and flexible structures with edges and corners. 236 It usually appears to be related to the velocity of the incoming flow and the relative 237

orientation of the fluid with respect to the structure, and is usually characterized by 238 low-frequency and high-amplitude oscillations [9]. The galloping energy is mostly 239 based on the principle of galloping, and the typical SDOF model of the galloping 240 energy harvester is shown in Fig. 10, while the governing equation of the model can 241 be written as[41] 242

(4) 243

where M, C, K are structural parameters related to the system, M is the mass of the 244 square cylinder, C is the damping of the system, K is the spring stiffness, w(t) is the 245

lateral displacement of the end of the bluff body, is the aerodynamic force of the 246

bluff body applied in the flow field. Tabesh et al. [42] transformed the circuit 247 parameters into mechanical parameters by performing a Laplace transform on Eq.(4), 248 using electrical damping Ce and electrical stiffness Ke to represent the effect of the 249 load circuit on the system, and decoupling the equation: 250

(5) 251

where the electrical damping and electrical stiffness are expressed as 252

(6) 253

Barrero-Gil and Abdelkefi et al. [43, 44] pointed out that, the time scale of the 254 structural oscillations characteristics of the galloping 2π/ω is much larger than the 255 characteristic time scale of the fluid passing the cylinder D/U, so the quasi-static 256

theory can be used to obtain the aerodynamic force . By using a polynomial 257

fitting approximation method, can be expressed as a cubic polynomial expansion 258

of the angle of attack α, where the polynomial coefficients are independent of the 259 Reynolds number, so 260

(7) 261

Here is the density of the incoming flow, U is the velocity of the incoming flow, S 262

represents the cross-sectional area of the square column in the vertical flow direction, 263 A1 and A3 are empirical coefficients related to the shape of the oscillator, the angle of 264

attack α can be written as (the rotation of the square column was 265

ignored). 266

(8) 267

( ) ( ) ( ) ( )( ) / ( ) ( ) 0

ZS

l

Mw t Cw t Kw t V(t) F tV t R C V t w t

θ

θ

+ + + =

+ − =

( )ZF t

( ) ( ) ( ) ( ) ( ) ( )e e ZMw t C C w t K K w t F t+ + + + =

2 2

2 2

( ) , 1 ( ) 1 ( )

Sl l

e eS Sl l

R C RK CR C R Cωθ θ

ω ω= =

+ +

( )ZF t

( )ZF t

2 2 31 3

1 1( )2 2Z a aF t SU A SU Aρ α ρ α= +

aρ

( ) /t U= α ω

22

1 32

2

2

1 1 ( )( ) ( ) ( )1 ( ) 2 2

( ) ( ) ( ) 01 ( )

la aS

ls

ls

l

R w tMw t C SUA SUA w tR C U

R CK w tR C

θ ρ ρω

ωθω

+ + − − +

+ + =+

One can regard the aerodynamic force on the square column as a nonlinear 268 damping element, so the damping term in the galloping mathematical model can be 269 expressed as the sum of a linear damping and a nonlinear damping, thus the damping 270 coefficient form is [45] 271

(9) 272

For the galloping energy harvester, the linear damping term determines the 273 threshold wind speed. By reasonably adjusting the structural parameters of the device 274 and the shape structure of the oscillator, energy harvesting can be achieved at a 275 relatively small wind speed. At the same time, the output energy efficiency increases 276 with the increase of the wind speed. The nonlinear damping term has a great influence 277 on the maximum amplitude of the harvester and provides a vibration mitigation effect 278 ensuring stable oscillations of the system. 279

280 Figure 10. Schematic of a bluff body subjected to galloping. 281

In the studies of the galloping energy harvesting, the applied aerodynamic force 282 FZ(t) of the bluff body is not only related to the structural parameters of the harvester 283 and the incoming wind speed, but also affected by the surface condition of the bluff 284 body. For the galloping energy harvester with relatively complicated structure, it is 285 always difficult to determine the aerodynamic forces. Javed et al. [46] used a 286 distributed parameters model to study the effects of different aerodynamic load 287 representations on the galloping harvesting. In the experiment, the polynomials 288 approximation of the aerodynamic force with different coefficients were used to 289 calculate the efficiency of the galloping energy harvesting under the same working 290 conditions. The results show that the maximum displacement and energy harvesting 291 efficiency of the harvester may change when different aerodynamic polynomials are 292 used. In order to study the influence of the wall on the aerodynamic forces, Soohwan 293 et al. [47] constructed a model of a galloping-based piezoelectric wind energy 294 harvester with a peripheral structure, and the structure of the harvester is shown in Fig. 295 11. Then, a new quasi-static aerodynamic model with two variables, the angle of 296 attack α, the nearest wall distance dy was proposed, and the theoretical model of the 297 energy harvester was established based on the Euler–Bernoulli beam theory and linear 298

2

12

2

3

1 linear 1 ( ) 2

1 ( ) nonlinear 2

laS

l

a

RC SUAR C

w tSUAU

θ ρω

ρ

+ − +

−

piezoelectricity. The experimental results show that the model can predict the limit 299 cycle oscillations of the bluff body well, and the accuracy (R2 > 0.99) is higher than 300 the model accuracy without considering the wall surface (R2 > 0.90). On the other 301 hand, the load circuit has a great influence on the galloping energy harvester [48-54]. 302 Tan et al. [48] first studied the effect of a load circuit with inductance on the 303 efficiency of the cantilever beam piezoelectric energy harvester. The result shows that 304 the maximum power output under the optimal resistance can be achieved by 305 connecting the inductor and the resistor in series or in parallel. At the same time, the 306 introduction of the inductance component in the load circuit can increase the 307 maximum output power at a high wind speed, reduce the displacement of the bluff 308 body, and improve the stability of the system. Then, the effects of the DC and AC 309 circuit interfaces on the efficiency of the energy harvester were explored [50]. It was 310 found that when the wind speed is small, the minimum threshold wind speed, the 311 maximum tip displacement of the bluff body and the maximum output power of two 312 kinds of energy harvesters are almost the same, but the harvester with the DC circuit 313 interface has smaller maximal electrical damping with larger optimal load resistance. 314 When the wind speed is high, the harvester with AC circuit interface can obtain higher 315 output power. Zhao et al. [52] compared the effects of the four common load circuit 316 interfaces (synchronous charge extraction circuit, series and parallel synchronous 317 switch inductor circuits, standard circuits) on the galloping energy harvesting. They 318 found that the synchronous charge extraction circuit is suitable for weak coupling and 319 higher wind speed conditions, and synchronous switch inductor circuits are suitable 320 for weak and moderate coupling as well as lower wind speed conditions. For high 321 terminal loads , a series synchronous switch inductor circuit should be used; for small 322 terminal loads, a parallel synchronous switch inductor circuit should be used. Under 323 the condition of strong coupling, the harvester with synchronous switch inductor 324 circuit and the standard circuit have the same output power, and a standard circuit 325 with a simpler structure is generally selected. In addition, Barrero-Gil et al. [55] 326 investigated the improvement of galloping energy harvester by actively rotating the 327 galloping bluff body. The experimental results showed that imposing externally a 328 rotation of the body proportional to the angle of attack could improve the energy 329 harvesting efficiency of the energy harvester, which provide a reference for improving 330 the galloping energy harvester. 331

332

Figure 11. Schematic for the GPWEH [47]. 333 The current research on the galloping energy harvesting can be divided into the 334

following streams: (1) The galloping-based energy harvester with nonlinear magnetic 335 forces [56-60]. Bibo et al. [56] compared the output voltage and output power of 336 galloping energy harvesters with different types of nonlinear forces (softening, 337 hardening, bi-stable) for different wind speeds, and the results showed that the 338 nonlinear forces had a great impact on the performance of galloping energy harvesters. 339 Yang et al. [59] investigated the performance of a double-beam piezo-magneto-elastic 340 wind energy harvester (DBPME-WEH) for different wind speeds. Compared with the 341 double-beam piezoelectric wind energy harvester (DBP-WEH), the critical wind 342 speed of the DBPME-WEH is reduced to 41.9%. (2) The shape and structure 343 optimization of a bluff body. Compared with the traditional prismatic structure, new 344 structures such as T-shaped, Y-shaped, and D-shaped, etc. have higher energy 345 conversion efficiency [61-68]. In addition, the surface structure of the bluff body has 346 also a great influence on the efficiency of galloping energy harvesters. There are 347 number of examples like the whale flipper biomimetic structure proposed by Ewere 348 et al. [69], the passive control of the column with PTC rough belts [70, 71], adding 349 attachment to bluff body surfaces [72-74]. Wang, Zhou et al. [72] proposed a novel 350 galloping-based piezoelectric energy harvester with Y-shaped attachment at the bluff 351 body surface (GPEH-Y), and studied the effect of the attachment on the energy 352 harvester. The schematic diagram of the device is shown in Fig. 12. Firstly, the lattice 353 Boltzmann method (LBM) was used to compare the vibration amplitude and 354 frequency of a smooth cylinder and cylinder with Y-shaped attachment at a varying 355 wind speed. It was found that the vibrations of the cylinder changed from vortex 356 induced vibrations to galloping by adding the attachment, and the results were further 357 verified by the wind tunnel experiments. Then these results were compared with the 358 performance of GPEH-Y, GPEF-Square and VIVPEH under different resistive loads 359 and wind speeds, and they are shown in Fig. 13. Compared to GPEH-Y and 360 GPEF-Square, the minimal threshold wind speed of the VIVPEH was lower and it 361 enters the frequency lock-in region earlier, but the bandwidth of a working wind 362 speed of VIVPEH (1m/s < U < 1.42m/s) is much smaller than that of GPEH-Y (U < 363 1.28m/s). In the operating range of a wind speed U ≤ 2m/s, GPEH-Y increases the 364 maximum output voltage by nearly 300% compared with VIVPEH, and the maximum 365 output power increases by nearly 400%. In addition, Ding et al. [74] compared the 366 performance of energy harvester with symmetrical fin-shaped rods (FSR) at different 367 placement angles, and the experimental results showed that the optimal placement 368 angle of FSR was 30⁰-60⁰. (3) Hybrid galloping energy harvesting. Compared with the 369 single-mode energy harvester, the harvester using galloping and vortex-induced 370 vibrations coupling [21, 22, 75], galloping and base-vibration coupling [76-79] can 371 improve energy harvesting efficiency and widen the bandwidth of the harvester. Zhao 372 et al. [79] proposed a hybrid energy harvesting device as shown in Fig. 14, which 373 introduces a high frequency mechanical stopper as a supplemental energy source to 374 improve the performance of the device. The experimental results show that the 375 working bandwidth and the energy harvesting efficiency of the hybrid device are 376

greatly improved compared with the original energy harvester. The bandwidth is 377 increased by nearly 8.5 times, and the efficiency of energy harvesting has increased 378 nearly twice under the wind speed of 5m/s and the base vibration acceleration of 379 1m/s2. 380

381

Figure 12. Schematic diagram of the GPEH-Y: (a) Equivalent schematic diagram; 382 (b) physical diagram in the wind tunnel test [72]. 383

384 Figure 13. Experimental comparison of the GPEH-Y, the VIVPEH, and the 385

GPEH-Square with different load resistances: (a) Output voltage; (b) output power 386 [72]. 387

388 Figure 14. the enhanced broadband wind and base vibration EH system [79]. 389

1.3 Flutter 390

Flutter is a typical two-dimensional aeroelastic instability phenomenon involving 391

bend and twist vibrations, which occur mostly in the high-speed flow field [80]. 392 Flutter can result in structural damages of the aircraft wings and tail in aerospace 393 structures [81]. Due to the existence of a phase difference between the instantaneous 394 aerodynamic force acting on the structure and the structural displacements where the 395 flutter appears, positive feedback can occur during the vibrations of the structure and 396 the aerodynamic force. As the structure constantly absorbs energy from the flow, the 397 amplitude of vibrations will increase continuously and diverge if the aerodynamic 398 damping is greater than the mechanical damping [9]. In terms of the energy harvesting 399 phenomenon, the flutter-based energy harvester have a great potential for 400 development because of self-excitation, divergence, and large amplitudes of 401 vibrations caused by flutter. 402

Santos et al. [82]studied the response of the harvester at high subsonic conditions 403 using a typical flutter energy harvesting model with a pitching structure, as shown in 404 Fig. 15. They found that the stiffness of the structure has a little influence on the 405 structural response, and the position of the elastic axis and the inertia parameters have 406 a great influence on the response. Ardito and Musci [83] studied the application of the 407 flutter energy harvesting in MEMS. In the study, they first discussed the modeling 408 method of the cantilever beam structure piezoelectric flutter energy harvester, then 409 studied the aerodynamic effect of the Reynolds number on the device, and verified the 410 feasibility of flutter energy harvesting. By analyzing the experimental results of Bruno 411 and Fransos [84], it is found that the mechanism of a cantilever beam flutter 412 instability may change with Reynolds number. In addition, they studied the effects of 413 RC load circuit and RLC load circuit on the device's energy harvesting efficiency. The 414 experimental results show that the RLC load circuit has higher efficiency than the RC 415 pure-resistance circuit. Rong et al. [85] performed a stability analysis on a flutter 416 energy harvester, which consisted of a thin plate and a flap hinged at its end, and 417 obtained the effect of a sheet size on the threshold wind speed. The results show that 418 when the aspect ratio of the thin plate increases, the minimal threshold wind speed 419 decreases, and the width of the flap has also a great influence on the threshold wind 420 speed. Tang et al. [86] studied the efficiency of a flutter energy harvester consisting of 421 a piezoelectric plate and a load circuit, which harvesting energy in different directions 422 of an incoming flow. The results provide a reference for the improvement of the 423 flag-type energy harvesting device. Pigolotti et al. [87] conducted out the wind tunnel 424 experiments and numerical linear analysis on the two-degree-of-freedom flutter model 425 to study its responses under the critical and supercritical conditions, as shown in Fig. 426 16. By optimizing the load circuit and structure of the energy harvester, the 427 performance of the harvester can be improved [88-94]. Grainger et al. [88]increased 428 the output power of the circuit by tuning resistors. Pasquato et al. [90] proposed that 429 the flutter energy harvester can be equipped with a dynamic adjustment system to 430 track and adjust the harvester to the maximum power output point, thereby improving 431 the stability and application range of the device. Hafezi et al. [91] added a moving 432 slider to the piezoelectric energy harvester with a cantilever beam structure to 433 improve the device performance by moving the slider. The device structure is shown 434 in Fig. 17. The experimental results show that the starting wind speed of the harvester 435

can be effectively adjusted and the output power can be increased by changing the 436 position of the slider. Chawdhury et al. [94] optimized the T-type cantilever beam 437 structure flutter energy harvester. In the simulation, the parameters such as the length, 438 width, and end height of the cantilever beam were optimized, and the output power of 439 the energy harvester was taken as the objective function. The optimization results 440 show that the output power of the harvester at low wind speed can be improved by 441 reasonably adjusting the parameters of the cantilever beam structure. When the wind 442 speed is 4m/s, the output power of the captive device can reach 0.65mW. 443

444

Figure 15. Schematic representation of the electric-aeroelastic model [82]. 445

446

Figure 16. Sketch of the two-degree-of-freedom flutter problem [87]. 447

448 Figure 17. Schematic top view for adaptive aeroelastic piezoelectric harvester setup 449

[91]. 450

1.4 Buffeting 451

Buffeting is a process of periodic vibration caused by the effects of upflow wakes 452 or natural turbulence, usually occurring in unstable flow fields. The mechanism of 453 buffeting is similar to that of VIVs, the magnitude of the fluid force is independent of 454

the structure motion, and the resonant frequency is affected by the natural frequency 455 of the structure [95]. Typically the governing equation of a buffeting SDOF system 456 can be expressed as 457

(10) 458

where M, Cst, K are mechanical parameters associated with the system, M is mass, Cst 459 is system damping, K is spring stiffness, and FMIM and FEIM are unsteady aerodynamic 460 forces of the fluid. 461

The buffeting energy harvester generally adopts a wake vortex-induced structural 462 vibrations design or a multi-column structure design. Hu et al. [96] constructed a 463 wake-induced vibrations harvester, which consists of a fixed cylinder and a 464 piezoelectric cantilever beam. In this device, the alternating vortices generated by the 465 fluid passing the rigid cylinder induce the vibrations of the piezoelectric beam behind 466 the cylinder and generate electric energy. At the same time, the device can adjust the 467 natural frequency of the oscillator by changing the size and shape of the oscillator. 468 Then Hu et al. proposed a model to calculate the optimal position of the induced 469 vortex, the optimal location of vortex shedding can be determined and the energy 470 harvesting efficiency can be optimized with the model. Although the multi-column 471 structure has the better performance of energy capture, the aerodynamic force on the 472 column is complicated due to the interference between the multiple cylinders. In order 473 to accurately predict the aerodynamic performance of the series of double cylindrical 474 vortex-induced vibrations energy-capturing devices (DSVIVEHS), Zhou et al. [97] 475 used the Boltzmann method to analyze the system. In the experiment, they first used 476 the D2Q9 model to establish a numerical solution model of the vortex-induced 477 vibrations of the cylindrical structure, and then verified the model by the wind tunnel 478 experiments. The numerical solution results are in good agreement with the wind 479 tunnel experiment results. Then they studied the performance of DSVIVEHS. The 480 experimental results show that the energy capture efficiency and working bandwidth 481 of DSVIVEHS can be increased by 6.8 times and 2.67 times, respectively, compared 482 with the single cylinder structure. Subsequently, Wang et al. [98] studied the 483 performance of a series of the square column and cylindrical captive energy device by 484 means of the coupling of electromechanical model and computational fluid dynamics. 485 The coupling calculation process is shown in Fig. 18. Firstly, the external force f of 486 vortex-induced vibrations piezoelectric energy harvester is obtained by using the 487 lattice Boltzmann method. The system response is obtained by substituting f into the 488 electromechanical coupling equation, and then the system response is used as the 489 initial condition for the next step. When the error precision meets the specified 490 requirements (the system reaches steady state) the iterative process stops. This method 491 is a good approach for the aerodynamic problems of the complex structures. Song et 492 al. [99] studied the layout optimization of vortex-induced vibrations energy harvester 493 with staggered four-cylinder structures. 494

( ) ( )st MIM EIMMw C w Kw F t F t+ + = +

495

Figure 18. The chart of the strong coupling computational process [98]. 496

Table 1 497

Summary of the current research on flow-induced vibration energy harvesting 498 Type Bandwith Fluid velocity Investigator Output

VIV

1.8-3.2m/s 3m/s Zhang et al. [25] 0.3mW 1.76-3.34m/s 2.8m/s Wang et al. [30] 0.0289mW

2-3.5m/s 2.7m/s Zhang et al. [38] 0.14mW 0.6m/s Zhao et al. [40] 16.55mW

0.1-0.3m/s 0.18m/s∗ Guilherme et al.

[44] 80mW

Galloping

≥1m/s 5m/s Liu et al. [67] 40V, 1.6mW ≥1.824m/s 2.646m/s Wang et al. [74] 1.6mW

≥3m/s 7m/s Noel et al. [77] 14.8mW ≥3m/s 5m/s(a0=1m/s2) Zhao et al. [81] 5.5mW

Flutter ≥15m/s 25m/s

Grainger et al. [91]

50mW

≥3.4m/s 5.2m/s Pasquato et al.

[93] 3.5mW

≥2m/s 8m/s Hafezi et al.

[94] 3.5mW

≥4m/s 8m/s Chawdhury et

al. [97] 5.3mW

Buffeting 2.48-5.36m/s 3.9m/s Zhou et al. [100] 0.125mW

2m/s∗ Hu et al. [99] 40V, 26mW

∗ represents the velocity of the water and the rest represents the velocity of the wind. 499

2 Flow induced vibration energy harvester 500

In recent years, with the further achievements in the flow-induced vibrations 501 research, new energy harvesting based on flow-induced vibrations theory have been 502 developed. Flow-induced vibrations energy harvesting can be adapted to use for wind 503 and hydro energy harvesting according to the properties of the incoming fluid. This 504 section mainly introduces the research progress and application of the two kinds of 505 energy harvesters. 506

2.1 Wind energy harvester 507

The traditional blade wind turbines are mainly used to harvest wind energy by the 508 electromagnetic induction principle. They have high requirements for a wind speed, 509 and generally are located in costal, offshore, and other high wind areas. They are 510 suitable for large-scale networking design. The Haliade-X 12MW, the world's 511 powerful offshore wind generator, has a rotor diameter of 220m and a power capacity 512 of 12MW [100]. But its mechanical structure is very complex, and the power 513 generation density is restricted by scale. Therefore, it is generally not suitable for 514 miniaturized design[101]. Besides, wind farms are usually placed far from the 515 consumers, which lead to losses, high maintenance costs, etc. Flow-induced vibrations 516 wind energy harvester converts wind energy into vibration energy by the 517 flow-induced vibrations principle and then converts vibration energy into electric 518 energy through the piezoelectric effect or electromagnetic induction principle. The 519 critical wind speed of the flow-induced vibrations wind energy harvester is affected 520 by the natural frequency and structural parameters of the harvester. The device has 521 low requirements for a wind speed, and its output voltage and power meet the 522 requirements of the sensor. Meanwhile, the structure is always very simple for the 523 flow-induced vibrations energy harvester and their size allows them to be used by 524 distributing them within the populated areas, close to the consumers. There is no any 525 gears, bearings, propellers and other mechanical parts, which significantly reduces 526 their reliability and increases maintenance costs. Therefore, such systems are more 527 suitable for miniaturized design and to use them as the energy source of WSNs system. 528 Moreover, such devices can be distributed inconspicuously over the towns and cities 529 on residential and commercial buildings, organizing an alternative network. 530

Vortex Bladeless, which is a new wind power generation equipment, is invented by 531 a Spanish company[7]. This harvester is designed to improve the efficiency of wind 532 energy harvesting and to solve the transportation, installation, and maintenance 533 problems of traditional wind turbines[102]. The structure of Vortex Bladeless is 534

shown in Fig. 19. This device utilizes the principle of vortex-induced vibrations to 535 make the cylinder vibrate transversely, and then convert the vibrations of the cylinder 536 into electric energy through the electromagnetic generator at the bottom. The cylinder 537 in the harvester adopts a new material such as carbon fiber to reduce the weight and 538 the natural frequency of the equipment, so that the starting wind speed of the cylinder 539 can be reduced to 3 m/s. Meanwhile, the device adjusts the stiffness of the system 540 according to the wind speed by means of a magnetic confinement to coordinate the 541 natural frequency of the system and the frequency of vortex shedding, and widen the 542 working bandwidth. The schematic diagram of the magnetic confinement is shown in 543 Fig. 20 [103]. In order to study the influence of the column structure on the bladeless 544 wind turbine (BWT), Chizfahm et al. [104] used four different cylinders to study the 545 BWT performance, as shown in Fig. 21. Among them, BWT1 and BWT2 adopt a 546 flexible equilateral section cylinder and flexible variable section cylinder respectively. 547 BWT3 adopts the combination of a flexible beam and rigid equal section cylinder, and 548 BWT4 adopts the combination of a flexible beam and rigid variable section. The 549 experiments show that BWT2 and BWT4 have better performance when the wind 550 speed is high (the vortex shedding frequency is higher than the natural frequency of 551 the structure), BWT1 and BWT3 have better performance when the wind speed is low 552 (the vortex shedding frequency is lower than the natural frequency of the structure). In 553 addition, compared with flexible column structure, the combination of flexible beam 554 and rigid column structure has better performance. Then, Yazdi et al. [105] found that 555 the vortex shedding frequency of BWT does not match the natural frequency of the 556 system under a high wind speed. They proposed a quadratic gain-scheduling 557 controller to improve the natural frequency of the structure and match the vortex 558 shedding frequency at high wind speeds. The output power of BWT with the 559 dispatching controller is up to 1kW. In addition to the above harvesters, Wang et al. 560 [106] studied a new type of the energy harvester based on vein structure 561 transformation, and its structure is shown in Fig. 22. The harvester uses triangular 562 leaves based on the venation structure of the leaves of dicotyledonous plants as 563 energy capture elements, and it uses the principle of VIVs to harvest wind energy. The 564 research shows that the efficiency of the energy harvester is greatly affected by the 565 venation structure, and the efficiency of the device with venation is 4~6 times higher 566 than that of the device without venation. Zhang et al. [107] constructed a curved beam 567 type vortex-excited vibrations enhanced energy harvester as shown in Fig. 23, which 568 makes the pressure on the curved beam approach the buckling strength by introducing 569 a spring to adjust the load on the bending beam. The experimental results suggest that 570 the output voltage and power of the device are significantly higher than that of the 571 traditional cantilever energy capture device, when the wind speed is close to 10m/s, 572 the effective output voltage can be increased by nearly 5 times. In addition, Gkoumas, 573 Wang et al. [108-110] proposed that the energy in the airflow of heating, ventilation 574 and air conditioning (HVAC) can be collected through the principle of flow-induced 575 vibrations, so as to optimize building energy consumption and realize the purpose of 576 building energy conservation. The MEMS energy harvester proposed by He et al. [111] 577 provides energy for the sensor by applying piezoelectric materials to the MEMS 578

system, which is of great significance for the miniaturization design of the wind 579 energy harvester. 580

581

Figure 19. Evolution of the mast diameter according to height [103]. 582

583 Figure 20. schematic diagram of Oscillator with a magnetic tuning system diagram 584

[103]. 585

586 Figure 21. The bladeless wind turbines; (a)BWT1 (b)BWT2 (c)BWT3 (d)BWT4 587

[104]. 588

589

Figure 22. The structures of the leaf-like wind energy harvester [106]. 590

591 Figure 23. Schematic of the piezoelectric wind energy harvester based on a 592

buckled beam [107]. 593 The common flutter type wind energy harvesters can be divided into piezoelectric 594

structure, electromagnetic structure, and electrostatic structure according to different 595 working mechanisms. The structure of the airfoil piezoelectric flutter energy harvester 596 is generally composed of a wing type oscillator, a hinge link structure, a flexible beam, 597 and a trapping circuit. When fluid passes the airfoil oscillator, it drives the bending 598 and vibrations of the piezoelectric beam while rotating, and convert fluid energy to 599 electric energy [112]. In order to improve the efficiency and stability of the harvester, 600 Orrego et al. [113] proposed a flutter energy harvester named "inverted flag", which 601 consists of a set of flexible piezoelectric film, a rigid-type rotating shaft and 602 self-aligning mechanism. A relatively simple structure is shown in Fig. 24. The 603 experimental results show that the device can output 1-5mW/cm3 at the wind speed of 604 5-9m/s, and maintain a continuous output of 0.1-0.4mW/cm3 even at low wind speeds 605 (2.5-4.5m/s), and be less affected by wind speed fluctuations. At the same time, the 606 "inverted flag" is dynamically adjusted by the self-aligning mechanism, the 607 temperature sensor data output is increased by nearly 20 times, the average daytime 608 temperature sensor outputs 1.5 times more data per minute, and provides the data 609 output every ten minutes at night, which basically is associated with the normal 610 operation of the temperature sensor. The electromagnetic flutter energy harvester 611 mainly collects wind energy through the principle of the electromagnetic induction. In 612 order to make full use of the mechanical energy generated by the fluttering pitching 613 motion and the vertical lifting motion, Liu et al. [114] proposed a nonlinear 614

electromagnetic energy trapping device as shown in Fig. 25, which can realize MDOF 615 cutting a magnetic sense line movement to improve the efficiency of energy 616 harvesting. Boccalero et al. [115] proposed a new coupled flutter energy harvester, 617 which is shown in Fig. 26. The device replaces the elastic material in the conventional 618 electromagnetic flutter energy capture device with a dielectric elastomer. It 619 implements the synergistic power generation of the electromagnetic and dielectric 620 elastomer by stretching and reducing the dielectric elastomer based on the vertical 621 lifting motion of the flutter, and then improves the efficiency of captive energy. 622 Aquino et al. studied the use of electromagnetic flutter energy capture devices in 623 buildings. With the development of intelligent smart cities, low-power small 624 appliances and milliwatt-class wireless sensors, data recorders and other small 625 power-consuming electronics will be extensively used. Therefore, it is a good choice 626 to use a flutter-type energy harvester to achieve an independent power supply [116, 627 117]. The electrostatic energy harvester is usually designed based on the principle of 628 the triboelectric charging. The flexible mold rubs against the fixed rail under the 629 action of the fluid to realize the transfer of an electric charge and convert the fluid 630 energy into electric energy. Perez et al. [118] tested the performance of an electrostatic 631 film with a size of 5 cm × 2 cm × 50 μm at a wind speed of 15 m/s. In the experiment, 632 Perez et al. [118] installed four sets of 1 cm × 2 cm electrodes on the sidewall behind 633 the film to collects the charge. The results show that the device's energy output can 634 reach 180μW. Phan et al. [119] proposed a nano-friction generator, which can harvest 635 wind energy based on the flutter principle, as shown in Fig. 27. The device is mainly 636 composed of a flutter film and rubber belt. When air passes through it, the flutter film 637 will vibrate and then generate electric energy by friction with the rubber belt. Under 638 normal operating conditions, the output power of the single-layer flutter 639 nanogenerator reaches 0.33μW. The output power can be increased through 640 multi-layer stacking to meet the energy demand of a small sensor. 641

642 Figure 24. Inverted flag [113]. 643

644 Figure 25. Schematic of a the electromagnetic aeroelastic energy harvester, and b the 645

plunge and pitch motions of the coil immersed in the magnetic field [114]. 646

647 Figure 26. Picture of FLEHAP device exploiting EMc(a), and a sketch of system 648

using both EMc and DEGs(b) [115]. 649

650 Figure 27. Aerodynamic and aeroelastic flutter-driven triboelectric nanogenerators 651

[119]. 652

2.2 Hydro energy harvester 653

In recent years, with the increasingly serious environmental problems in the oceans, 654 rivers, and lakes, environmental ecology has gradually become an important factor 655 restricting the development of hydro energy harvesting technology. In addition, the 656 complex and changeable water environment has also brought great difficulties to the 657 deployment of energy harvesters. Many domestic and foreign researchers have 658 recently conducted in-depth research on water energy harvesting [120-128]. The 659 structure of the fluid-induced vibrations water energy harvester is simple and can 660 adapt to the harsh and complex environment, which is suitable for underwater work. 661 In addition, the fluid-induced vibrations energy harvesters has little impact on the 662 environment and ecology, and they will not cause much impact on the surrounding 663 environment [129]. 664

At present, the most common energy harvesters include horizontal and vertical axis 665 turbines, oscillating hydrofoil power generation devices, venturi differential pressure 666 turbines, Archimedes screw turbines, tidal kite turbines, water storage energy 667 harvesting, VIVACE harvester, etc.[130] The VIVACE harvester was proposed by 668 Bernitsas and Raghavan et al. [6] at the University of Michigan, and its structure is 669 shown in Fig. 28. The harvester is mainly composed of a vibrating cylinder, a 670

transmission structure, a generator and other parts. Under the action of a water flow 671 the cylinder in vortex-induced vibrations converts the fluid energy into vibrational 672 energy, which is then transmitted energy through, then the transmission structure can 673 transform a linear motion into the rotary motion of the rotor in the generator, finally 674 the fluid energy is converted into electrical energy. The experimental results show that 675 the harvester has a wide operating range, and it can still operate normally and 676 maintain a high capture energy efficiency even at the flow speed as low as 0.25m/s, 677 thereby validating the water flow energy harvesting. The success of VIVACE is of 678 great significance, and it has greatly promoted the development of the research on 679 water energy harvesting. The bionic structure like an airfoil harvests energy by 680 simulating the swing of the tail of the animal, and it has a better research prospect due 681 to its great hydrodynamic properties [131]. BioSTREAM [132] is a marine tidal 682 energy harvesting facility developed by BPS company in Australia, and the model is 683 shown in Fig. 29. The harvester is mainly composed of a fixed base, a tail structure, a 684 hydraulic cylinder, O-Drive (DC power generation device) and other parts. The attack 685 angle of the tail fin and the direction of the incoming flow are kept consistent by 686 active control. Under the action of the fluid lift force, the tail fin structure rotates 687 around the fixed base to compress the fluid in the tail hydraulic cylinder. Finally, the 688 O-Drive uses high-pressure fluid to generate DC power, which realizes the conversion 689 of fluid energy to electric energy. Barbarelli et al. [133] proposed a new offshore 690 energy harvester, which is shown in Fig. 30. It is mainly composed of an airfoil blade, 691 a four-link connection structure, a piston pump, a reservoir, a hydraulic generator set 692 and other parts. The device turns the tidal horizontal flow into the up-down movement 693 of the blades, and drives the pistons to reciprocate through the four-bar structure, then 694 pushes the generator set to work by the pressure difference, the conversion of tidal 695 energy into electricity can be finally realized. The harvester arranges vulnerable parts 696 including generator sets on the shore, and the blade oscillators are immersed in the 697 offshore sea level, so that it reduces the cost of installation and maintenance. However, 698 it will reduce the efficiency of the energy capture due to friction and wear of the 699 connecting mechanism at the same time. Subsequently, Barbarelli et al. [134] assessed 700 the performance of the energy harvester, the preliminary evaluation suggests that 701 when the tidal flow velocity reaches 3m/s, its output power will exceed 120kW and 702 the energy conversion efficiency will reach 23% for a device with a blade length of 703 8m and an upper and lower migration range of 5m. 704

705

Figure 28. The structures of VIVACE [6]. 706

707

Figure 29. BioSTREAM [132]. 708

709 Figure 30. System configuration and blade particular [133]. 710

711

Table 2 712

Summary of flow induced vibration energy harvester mentioned above 713 Type Bandwith Fluid velocity Investigator Output

Wind energy harvester

3m/s-12m/s Nominal speed Vortex

Bladeless[103] 100W

≥1m/s 20m/s Yazdi et al. [107] 10000W ≥6m/s 10m/s Wang et al. [108] 0.457μW/cm2

≥4m/s 14m/s Zhang et al.

[109] 61.8μW

≥3.6m/s 7m/s Wang et al. [112] 275mW ≥4m/s 7.3m/s He et al. [113] 0.14μW

≥4.2m/s 9m/s Inverte flag[114] 5mW/cm2

≥8.2m/s 13m/s Liu et al. [115] 40mW

≥2.5m/s 6m/s Boccalero et al.

[116] 22mW

≥2m/s 15m/s Perez et al. [119] 180mW ≥15m/s - Phan et al. [120] 71μW

Hydro energy harvester

≥0.25m/s 0.35m/s Sun[124] 1.3mW ≥0.17m/s 0.33m/s Zhang[125] 1.02μW ≥0.3m/s 1.5m/s Zhu[126] 75.89mW/m ≥0.2m/s 1m/s Kong[127] 60mW ≥0.43m/s 1.31m/s wu[128] 16W

1.5m/s VIVACE[132] 100MW

BioSTREAM

[133] 250kW

≥3m/s 5m/s Barbarelli et al.

[134] 470kW

714

3 Prospects and Challenges 715

Based on the different mechanisms of flow-induced vibrations, this paper 716 summarizes the research progress of flow-induced vibrations energy harvesting of 717 four types: vortex-induced vibrations, galloping, flutter, and buffeting. According to 718 the different sources of fluid energy, the common wind and water energy harvesters 719 are discussed. 720

The energy harvesting by flow-induced vibrations has a great application 721 perspective and can solve the problem of powering wireless sensors networks. With 722 the rapid development of WSNs and Internet of Things technology, the flow-induced 723 vibrations energy harvesters will be proliferating into these and other sectors where 724 alternative, independent and distributed energy sources are required. Of course, one 725 must also recognize the urgent problems that the flow-induced vibrations energy 726 harvesting technology faces right now [9]. For example, the vibration frequency of 727 Vaneless generators is lower than that of others, which may cause serious infrasound 728 crisis once it is adapted widely. Due to the size and material limitation of piezoelectric 729 energy harvesters, the power generation is limited, which makes it difficult to meet 730 the actual requirements of sensors. These devices still need research and optimization 731 to work effectively and sustainably in spite of geographical environment, weather and 732 others factors. Although the water energy harvester has a little impact on the 733 ecosystem, it also has some problems, for instance a low energy conversion rate. At 734 present, most of the flow-induced vibrations energy harvesters are still at their 735 experimental stage, and there is still a long way ahead before their deployment and 736 wider proliferation is achieved. Meanwhile, the flow-induced vibrations energy 737 harvesting technology can be combined with the current mature photovoltaic power 738 generation technology, the fan power generation technology, and the excitation 739 vibration energy harvesting technology to ensure the normal operation of the 740 flow-induced vibrations energy-trapping devices under multiple working conditions. 741 742

Acknowledgement 743

The authors gratefully acknowledge the support provided by the National Natural Science 744 Foundation of China (No.51606171), and the China Postdoctoral Science Foundation (No. 745 2019M652565). 746

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