Numerical study on the energy extraction performance by flapping foils in a density stratified flow

Wang, Jiadong; Deng, Jian; Kandel, Prabal; Sun, Liping

doi:10.1016/j.jfluidstructs.2023.103865

Cited by 5 publications

(4 citation statements)

References 45 publications

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“…The present numerical solver has been employed to simulate the stratified flow around both the stationary object (Deng & Kandel 2022) and the moving body (Kandel & Deng 2022; Wang et al. 2023). Extensive verification and validation of the computational method can be found in these studies.…”

Section: Methodsmentioning

confidence: 99%

High propulsive performance by an oscillating foil in a stratified fluid

Wang,

Kandel,

Deng

2024

J. Fluid Mech.

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We investigate numerically the propulsion characteristics of an oscillating foil undergoing coupled heave and pitch motion in a linearly density-stratified flow. A parameter space defined by the internal Froude number ( $1 \le Fr \le 10$ ) and the maximum angle of attack ( $5^\circ \le {\alpha _0} \le 30^\circ$ ) is considered in our study. The results demonstrate a significant enhancement in both thrust production and propulsive efficiency due to the stratification influence. Notably, the highest efficiency exceeding $80\,\%$ is achieved under moderate stratification conditions, surpassing the performance observed in a homogeneous fluid. We attribute this optimum performance to the proper match between the stratification effect and foil kinematics, which gives rise to intense vortex interactions and sufficient wave–mean flow interactions in the near wake of the oscillating foil. Consequently, the energy is transferred towards wake structures to form a high-intensity momentum jet in close proximity to the foil's trailing edge, indicating efficient propulsion. Furthermore, we find that the stratifications within the moderate-to-strong transitional regime display a reduced dependence of propulsive efficiency on the maximum angle of attack, primarily due to the delaying and alleviating effects on dynamic-stall events. Such a mechanism enables the oscillating foil to maintain a satisfactory performance by sufficiently high angles of attack without the penalty of stall events. Based on our findings, we propose that animals or artificial vehicles utilising oscillatory propulsion can benefit from the presence of density stratification in the surrounding fluid.

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Section: Methodsmentioning

confidence: 99%

High propulsive performance by an oscillating foil in a stratified fluid

Wang,

Kandel,

Deng

2024

J. Fluid Mech.

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“…These studies emphasize the importance of the attack angle and the incoming flow deflector placement for maximizing power generation efficiency [29]. An analysis has been conducted on how density-stratified flow affects energy extraction efficiency, particularly focusing on the amplitude of pitching movements [30].…”

Section: Introductionmentioning

confidence: 99%

Numerically Investigating the Energy-Harvesting Performance of an Oscillating Flat Plate with Leading and Trailing Flaps

Saleh,

Sohn

2024

Energies

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This study investigates the power generation capability of an oscillating wing energy harvester equipped with two actively controlled flaps positioned at the leading and trailing flaps of the wing. Various parameters, including flap lengths and pitch angles for the leading flap and trailing flap, are explored through numerical simulations. The length of the main wing body ranges from 40% to 65% of the chord length, c, while the leading and trailing flaps vary accordingly, summing up to the total length of the flat plate c = 100%. The pitch angles of the two flaps are adjusted within predefined limits. The pitch angle for the leading flap varies between 25° and 55°, while the trailing flap’s angle ranges from 10° to 40° across 298 different simulation scenarios. The results indicate that employing both leading and trailing flaps enhances the power output compared to a wing with a single flap configuration. The trailing flap deflects the incoming fluid more vertically, while the leading flap increases pressure difference across the surface of the main wing body, synergistically improving overall performance. The power output occurs at a specific length percentage: a leading flap of 30%, a main wing body of 50%, and a trailing flap of 20%, with pitch angles of 50°, 85°, and 30°, respectively, increasing the output power increments by 4.39% compared to a wing with a leading flap, 4.92% compared to a wing with a trailing flap, and 28.24% compared to a single flat plate. The highest efficiency for the specified length percentages is 40.37%.

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“…Various deflector designs have been explored to enhance power output in flapping foil energy harvesters, focusing on the angle of attack and the distance of upstream deflectors to the hydrofoil, highlighting their impact on power generation efficiency [36]. The influence of stratified density flow on energy output was analyzed, particularly in relation to pitching movement amplitude [37].…”

Section: Introductionmentioning

confidence: 99%

Power Extraction Performance by a Hybrid Non-Sinusoidal Pitching Motion of an Oscillating Energy Harvester

Saleh,

Sohn

2024

Energies

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This study proposes a hybrid pitching motion for oscillating flat plates aimed at augmenting the energy extraction efficiency of an energy harvester. The proposed hybrid pitching motion, within the first half cycle, integrates a non−sinusoidal movement starting at t/T = 0 and progressing to t/T = 0.25, with a sinusoidal movement initiating after t/T > 0.25 and continuing to t/T = 0.5. The second half of the cycle is symmetric to the first half but in the opposite direction. The calculated results show that the proposed hybrid pitching motion outperforms both the sinusoidal and the non−sinusoidal motions. The hybrid pitching motion merges the merits of both the sinusoidal and non−sinusoidal motions to optimize pitch angle variation. This integration is pivotal for enhancing the overall power output performance of an oscillating energy harvester characterized by momentum change that enhances the orientation of the heaving movement, smoother motion transitions, and consistent energy harvesting. The power generation is obtained at wing pitch angles of 55°, 65°, 70°, 75°, and 80° during a hybrid pitching motion. The proposed hybrid pitching motion, set at a pitch angle of 70°, achieves a maximum power output that exceeds the oscillating flat plate using a sinusoidal pitching motion by 16.0% at the same angle.

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Numerical study on the energy extraction performance by flapping foils in a density stratified flow

Cited by 5 publications

References 45 publications

High propulsive performance by an oscillating foil in a stratified fluid

High propulsive performance by an oscillating foil in a stratified fluid

Numerically Investigating the Energy-Harvesting Performance of an Oscillating Flat Plate with Leading and Trailing Flaps

Power Extraction Performance by a Hybrid Non-Sinusoidal Pitching Motion of an Oscillating Energy Harvester

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