Optimal Leading Edge Vortex Formation of a Flapping Foil in Energy Harvesting Regime

2017 ◽  
Author(s):  
Firas F. Siala ◽  
Alexander D. Totpal ◽  
James A. Liburdy
Keyword(s):  
Energy Harvesting ◽  
Vortex Formation ◽  
Leading Edge ◽  
Flux Analysis ◽  
Leading Edge Vortex ◽  
Flapping Foil ◽  
Flow Energy ◽  
Edge Vortex ◽  
Formation Number ◽  
Harvesting Regime

An experimental investigation is conducted to study the leading edge vortex (LEV) evolution of a simultaneously heaving and pitching foil operating in the energy harvesting regime. Two dimensional particle image velocimetry measurements are collected in a wind tunnel at reduced frequencies of k = fc/U = 0.05–0.20. Vorticity flux analysis is performed to calculate the constant C in the vortex formation number equation proposed by J. O. Dabiri [1], and it is shown that for a flapping foil operating in the energy harvesting regime, this constant is approximately equal to 1.33. We demonstrate that the optimal LEV formation number (T̂max ≈ 4) is achieved at k = 0.11, which is well within the range of optimal reduced frequency for energy harvesting applications (k = 0.1–0.15). This suggests that the flow energy extraction is closely related to the efficient evolution process of the LEV.

Numerical investigation of the power extraction mechanism of flapping foil tidal energy harvesting devices

2018 ◽  
Vol 30 (2) ◽  
pp. 193-211 ◽  
Author(s):  
Maryam Pourmahdavi ◽  
Mohammad Naghi Safari ◽  
Shahram Derakhshan
Keyword(s):  
Energy Harvesting ◽  
Stokes Equations ◽  
Critical Role ◽  
Pressure Coefficient ◽  
Leading Edge ◽  
Energy Extraction ◽  
Leading Edge Vortex ◽  
Power Extraction ◽  
Flapping Foil ◽  
Edge Vortex

The flapping foil hydrokinetics turbine is a new method to generate energy from incoming flow field. The numerical simulations have been performed computationally by using two-dimensional unsteady Reynolds-averaged Navier–Stokes equations. It was found that the maximum energy efficiency reached about 35.2% when the reduced frequency was 0.11; at this time, the foil experienced a light dynamic stall and two opposite-sign vorticities were shed from the foil per half of the cycle. This report also studied the energy extraction performance of flapping foil device and the correlation between the foil kinematic parameters and the flow fields around it at actual operating Reynolds number comprehensively. In addition, the vortex variation and the pressure coefficient distribution along the foil’s surface were used to demonstrate the mechanism of flapping foil energy generation turbine. The creation and shedding of the leading edge vortex played the critical role in energy transformation between the flow fluid and energy harvesting systems. Therefore, if the timing of the leading edge vortex generation and shedding is controlled, the energy extraction efficiency can be increased considerably.

3D Effects in the Wake Vortex Formation of an Elliptic Flat Plate in Hover

2017 ◽  
Author(s):  
Vivek Nair ◽  
Siddarth Chintamani ◽  
B. H. Dennis
Keyword(s):  
Flat Plate ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Elliptic Geometry ◽  
3D Effects ◽  
Edge Vortex ◽  
Formation Number ◽  
Vorticity Transport

A Numerical Analysis is conducted to investigate the Leading Edge Vortex (LEV) dynamics of an elliptic flat plate undergoing 2 dimensional symmetric flapping motion in hover. The plate is modeled with an aspect ratio of 3 and a flapping trajectory resulting in Reynolds number 225 is studied. The leading edge vortex stability is analyzed as a function of the non dimensional formation number and a vorticity transport analysis is carried to understand the flux budgets present. The LEV formation number is found to be 2.6. The results of vorticity analysis show the highly three dimensional nature of the LEV growth for an elliptic geometry.

Force Production Mechanisms of a Heaving and Pitching Foil Operating in the Energy Harvesting Regime

2018 ◽  
Author(s):  
Firas F. Siala ◽  
Michael W. Prier ◽  
James A. Liburdy
Keyword(s):  
Energy Harvesting ◽  
Force Production ◽  
Time History ◽  
Leading Edge ◽  
Total Force ◽  
Vertical Force ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Force Time ◽  
Harvesting Regime

The influence of vortex dynamics on the force production of a heaving and pitching foil operating in the energy harvesting regime is studied experimentally using 2C-PIV. Results are obtained for reduced frequencies in the range of k = fc/U = 0.06 to 0.14. The flow induced vertical force-time history during cyclic operation is evaluated from PIV data by using the impulse-based derivative moment transformation method. The contribution of each term in the equation is investigated. The results show that the leading edge vortex has the largest contribution to the total force, whereas the trailing edge vortex is shown to contribute negatively. In addition, the dynamics of the leading edge vortex are further analyzed by measuring the circulation and trajectory relative to the foil. It is shown that the force is not only dependent on the circulation magnitude, but also on the LEV foil-normal and chord-wise trajectories. The force-time history for all reduced frequencies exhibit two main distinct peaks. The primary peak is generated when the leading edge vortex forms. The secondary peak, on the other hand, is formed when the chord-wise convection of the leading edge vortex increases, as well as when the LEV is closer to the foil surface during the reversal of pitching motion.

scholarly journals Video: Leading edge vortex formation in aquatic swimming

2014 ◽  
Author(s):  
Mohsen Daghooghi ◽  
Richard G. Bottom ◽  
Iman Borazjani
Keyword(s):  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Initiation of Leading-Edge-Vortex Formation on Finite Wings in Unsteady Flow

2015 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Sachin Aggarwal ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Effects of Reynolds number on leading-edge vortex formation dynamics and stability in revolving wings

2021 ◽  
Vol 931 ◽  
Author(s):  
Long Chen ◽  
Luyao Wang ◽  
Chao Zhou ◽  
Jianghao Wu ◽  
Bo Cheng
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Numerical Methods ◽  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Formation Dynamics ◽  
Edge Vortex ◽  
Vorticity Balance ◽  
Vortex Compression

The mechanisms of leading-edge vortex (LEV) formation and its stable attachment to revolving wings depend highly on Reynolds number ( $\textit {Re}$ ). In this study, using numerical methods, we examined the $\textit {Re}$ dependence of LEV formation dynamics and stability on revolving wings with $\textit {Re}$ ranging from 10 to 5000. Our results show that the duration of the LEV formation period and its steady-state intensity both reduce significantly as $\textit {Re}$ decreases from 1000 to 10. Moreover, the primary mechanisms contributing to LEV stability can vary at different $\textit {Re}$ levels. At $\textit {Re} <200$ , the LEV stability is mainly driven by viscous diffusion. At $200<\textit {Re} <1000$ , the LEV is maintained by two distinct vortex-tilting-based mechanisms, i.e. the planetary vorticity tilting and the radial–tangential vorticity balance. At $\textit {Re}>1000$ , the radial–tangential vorticity balance becomes the primary contributor to LEV stability, in addition to secondary contributions from tip-ward vorticity convection, vortex compression and planetary vorticity tilting. It is further shown that the regions of tip-ward vorticity convection and tip-ward pressure gradient almost overlap at high $\textit {Re}$ . In addition, the contribution of planetary vorticity tilting in LEV stability is $\textit {Re}$ -independent. This work provides novel insights into the various mechanisms, in particular those of vortex tilting, in driving the LEV formation and stability on low- $\textit {Re}$ revolving wings.

Optimal frequency for flow energy harvesting of a flapping foil

2011 ◽  
Vol 675 ◽  
pp. 495-517 ◽  
Author(s):  
QIANG ZHU
Keyword(s):  
Energy Harvesting ◽  
Vortex Shedding ◽  
Leading Edge ◽  
Energy Extraction ◽  
Flapping Foil ◽  
Flow Energy ◽  
Performance Point ◽  
High Efficient ◽  
Harvesting Efficiency ◽  
Energy Harvesting Efficiency

Inspired by the correlation between the propulsion efficiency of a flapping foil propeller and stability of the wake behind it (which leads to the optimal Strouhal number for propulsion), we numerically simulated a heaving/pitching foil in energy harvesting regime, and investigated the relation between wake stability and the energy harvesting efficiency. The base flow is computed using a Navier–Stokes algorithm and the stability analysis is performed via the Orr–Sommerfeld equation. The wake is found to be convectively unstable and the frequency of the most unstable mode fw is determined. The case when fw ~ f coincides with maximum energy harvesting efficiency of the system (f is the frequency of foil oscillation), suggesting that flow energy extraction is closely related to efficient evolution of the wake. This occurs at a frequency of f ~ 0.15 (f is normalized by the chord length and the flow speed), under the constraint that there is significant vortex shedding from the leading edge at sufficiently large effective angles of attack. Indeed, this ‘foil–wake resonance’ is usually associated with multi-vortex shedding from the leading edge. Furthermore, detailed examination of energy extractions from the heaving and the pitching motions indicates that near the optimal performance point the average energy extraction from the pitching motion is close to zero. This suggests the feasibility of achieving high-efficient energy harvesting through a simple fully passive system we proposed earlier in which no activation is needed.

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