Experimental Study on Mean Thrust of Two Plunging Wings in Tandem

Gong, Wuqi; Jia, Bo Bo; Xi, Guang

doi:10.2514/1.j053452

Cited by 22 publications

(15 citation statements)

References 35 publications

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“…These have the form of parallel 'ridges' and 'valleys'. This has previously been observed for single frequencies (Boschitsch et al 2014;Gong et al 2015Gong et al , 2016, but until now this effect has never been observed over a range of frequencies. The fact that such a large thrust augmentation occurs for all these Strouhal numbers shows that the effect is important over a wide range of conditions.…”

Section: Results From Full Simulationsmentioning

confidence: 62%

“…Previous studies have shown that the force production on the hind foil of a tandemfoil configuration is affected by the phase difference in the kinematics between the fore and hind foils (ϕ) and the inter-foil spacing (S) Rival et al 2011;Kumar & Hu 2011;Broering & Lian 2010;Kinsey & Dumas 2012;Lian et al 2014;Boschitsch et al 2014;Gong et al 2015Gong et al , 2016. This effect has been addressed as "wake recapture", "wing/wake interaction", or "thrust augmentation For the purposes of this work, "performance augmentation" is deemed the most suitable description, as this term accounts for the augmentation of both thrust and efficiency.…”

Section: Introductionmentioning

confidence: 99%

“…Many studies have investigated both the phase and spacing, but at only one flapping frequency Kumar & Hu 2011;Boschitsch et al 2014;Gong et al 2015Gong et al , 2016. One study has considered the effects of both spacing and phase at different flapping frequencies, or Strouhal numbers (Broering & Lian 2010), although the parameter space was sparse and the experimental data consisted of combined forces of both foils, with very little information on the flowfield.…”

Section: Introductionmentioning

confidence: 99%

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Performance augmentation mechanism of in-line tandem flapping foils

2017

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The propulsive performance of a pair of tandem flapping foils is sensitively dependent on the spacing and phasing between them. Large increases in thrust and efficiency of the hind foil are possible, but the mechanisms governing these enhancements remain largely unresolved. Two-dimensional numerical simulations of tandem and single foils oscillating in heave and pitch at a Reynolds number of 7,000 are performed over a broad and dense parameter space, allowing the effects of inter-foil spacing (S) and phasing (ϕ) to be investigated over a range of non-dimensional frequencies (or Strouhal number, St). Results indicate that the hind foil can produce from no thrust, to twice the thrust of a single foil depending on its spacing and phasing with respect to the fore foil, which is consistent with previous studies that were carried out over a limited parameter space. Examination of instantaneous flowfields indicate that high thrust occurs when the hind foil weaves in between the vortices that have been shed by the fore foil, and low thrust occurs when the hind foil intercepts these vortices. Contours of high thrust and minimal thrust appear as inclined bands in the S − ϕ parameter space and this behaviour is apparent over the entire range of Strouhal numbers considered (0.2 St 0.5). A novel quasi-steady model that utilises kinematics of a virtual hind foil together with data obtained from simulations of a single flapping foil shows that performance augmentation is primarily determined through modification of the instantaneous angle of attack of the hind foil by the vortex street established by the fore foil. This simple model provides estimates of thrust and efficiency for the hind foil, which is consistent with data obtained through full simulations. The limitations of the virtual hind foil method and its physical significance is also discussed.

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Section: Results From Full Simulationsmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Performance augmentation mechanism of in-line tandem flapping foils

2017

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“…At the top and bottom of the flapping stroke, these vortices separate from the wing and are shed downstream to create two lines of vortices of alternating sign behind the wing, known as a 'vortex street' [16][17][18]. Thus, if another wing is present behind the first, these vortices and induced velocities will affect the performance (thrust and efficiency) of the hind wing [19][20][21][22][23][24][25][26][27]; this effect is known as performance (or thrust or efficiency) augmentation, and is strongest for certain spacing and phase differences between the wings, shown by a variety of studies [19][20][21][22][23][24][25][26][27][28][29][30], including on dragonfly flight [28,29] and the flocking of migrating birds [30].…”

Section: Introductionmentioning

confidence: 99%

The four-flipper swimming method of plesiosaurs enabled efficient and effective locomotion

et al. 2017

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The extinct ocean-going plesiosaurs were unique within vertebrates because they used two flipper pairs identical in morphology for propulsion. Although fossils of these Mesozoic marine reptiles have been known for more than two centuries, the function and dynamics of their tandem-flipper propulsion system has always been unclear and controversial. We address this question quantitatively for the first time in this study, reporting a series of precisely controlled water tank experiments that use reconstructed plesiosaur flippers scaled from well-preserved fossils. Our aim was to determine which limb movements would have resulted in the most efficient and effective propulsion. We show that plesiosaur hind flippers generated up to 60% more thrust and 40% higher efficiency when operating in harmony with their forward counterparts, when compared with operating alone, and the spacing and relative motion between the flippers was critical in governing these increases. The results of our analyses show that this phenomenon was probably present across the whole range of plesiosaur flipper motion and resolves the centuries-old debate about the propulsion style of these marine reptiles, as well as indicating why they retained two pairs of flippers for more than 100 million years.

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“…Supporting this argument, there have been extensive research efforts explaining energetic benefits of animals in collectives; ranging from a 15% thrust boost for fish schools [2], to 11 − 14% of metabolic energy savings for white pelicans [3]. So far this problem has been studied mostly for propulsors in in-line arrangements [5][6][7][8][9][10][11][12][13][14][15], as well as mixtures of side-by-side and in-line arrangements [15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Unsteady Performance of Finite-Span Pitching Propulsors in Side-by-Side Arrangements

Kurt

Moored

2018

2018 Fluid Dynamics Conference

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Experimental measurements are presented on the performance of two finite-span pitching wings with an aspect ratio of AR = 2 interacting in a side-by-side arrangement. Experiments are conducted for various synchronies and cross-stream spacings. The thrust, power and lift coefficients as well as the efficiency are reported for both the individual wings and the collective. The collective thrust and power consumption are found to increase while the efficiency decreases during out-of-phase oscillations (φ = π) for close spacings of Y * ≤ 0.75. Similarly, the collective thrust and power consumption are found to decrease while the efficiency increases during inphase oscillations (φ = 0) for spacings of Y * ≤ 1.125. In contrast to this trade-off between improved thrust or efficiency, there are conditions such as at Y * = 1 and φ ≈ π/2 and 3π/2 that give a 20% increase in collective thrust and 17% increase in collective efficiency at the same time. It is further demonstrated that the direction of the collective lift shows a dependence on both the synchrony and the spacing.

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Experimental Study on Mean Thrust of Two Plunging Wings in Tandem

Cited by 22 publications

References 35 publications

Performance augmentation mechanism of in-line tandem flapping foils

Performance augmentation mechanism of in-line tandem flapping foils

The four-flipper swimming method of plesiosaurs enabled efficient and effective locomotion

Unsteady Performance of Finite-Span Pitching Propulsors in Side-by-Side Arrangements

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