Influence of three-dimensionality on propulsive flapping

Zurman-Nasution, Andhini Novrita; Ganapathisubramani, Bharathram; Weymouth, Gabriel

doi:10.1017/jfm.2019.1078

Cited by 39 publications

(38 citation statements)

References 32 publications

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“…2008, 2009). Although three-dimensional effects compromise the coherence of these structures (Zurman-Nasution, Ganapathisubramani & Weymouth 2020), the formation and subsequent deflection of the dipole maintains its quasi-two-dimensional nature (Couder & Basdevant 1986; Godoy-Diana et al. 2008).…”

Section: Introductionmentioning

confidence: 99%

Deflected wake interaction of tandem flapping foils

2020

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Section: Introductionmentioning

confidence: 99%

Deflected wake interaction of tandem flapping foils

2020

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“…Meanwhile, the tip distance to the maximum spanwise domain is 3.2 C . The grid convergence study provided in (20) using an infinite foil with a span length of 6 C in Re = 5300 as a comparison of time-averaged thrust co-efficient for different resolutions. The force coefficient converges to within 7% of the finer simulations (for 2D and 3D simulation) using a resolution of C /Δ x = 128.…”

Section: Methodsmentioning

confidence: 99%

“…Most analytical studies using lifting-line theory indicate sweep is advantageous, increasing the thrust and propulsive efficiency (16)(17)(18). While such methodologies are effective at determining lift characteristics on steady wings, they cannot model unsteady rotational three-dimensional flow, including the evolution of vortices that form at the fin's leading edge and tip which lead to the high forces observed in flapping foil propulsion (19,20). While some experimental studies have measured a small flap- ping propulsive benefit to sweep, the effect is smaller than the analytic studies and other experiments have found no impact at all.…”

Section: Introductionmentioning

confidence: 99%

Fin sweep angle does not determine flapping propulsive performance

Zurman-Nasution

Ganapathisubramani

Weymouth

2020

Preprint

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The importance of the leading-edge sweep angle of propulsive surfaces used by unsteady swimming and flying animals has been an issue of debate for many years, spurring studies in biology, engineering, and robotics with mixed conclusions. In this work we provide results from an extensive set of three-dimensional simulations of finite foils undergoing tail-like (pitch-heave) and flipper-like (twist-roll) kinematics for a range of sweep angles while carefully controlling all other parameters. No significant change in force and power is observed for tail-like motions as the sweep angle increases, with a corresponding efficiency drop of only ≈ 2%. Similar findings are seen in flipper-like motion and the overall correlation coefficient between sweep angle and propulsive performance is 0.1-6.7%. This leads to a conclusion that fish tails or mammal flukes can have a large range of potential sweep angles without significant negative propulsive impact. A similar conclusion applies to flippers; although there is a slight benefit to avoid large sweep angles for flippers, this could be easily compensated by adjusting other hydrodynamics parameters such as flapping frequency, amplitude and maximum angle of attack to gain higher thrust and efficiency.

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“…where f is the cycle frequency of flapping and a and θ 0 are the amplitudes of heave and pitch at each section. The term θ bias = 10 • is a pitch bias angle used to ensure non-zero average mean lift as in Zurman-Nasution et al [17] and the phase difference is set to ψ = 90 • to maximize performance [33]. In order to isolate the amplitude (which varies section by section) from the frequency, these motions are characterized as…”

Section: Ii1 Geometry and Kinematicsmentioning

confidence: 99%

“…Finally, even on an infinite wing with no tip effect or mean spanwise flow, 3D evolution of the vortex wake limits strip theory applications. Zurman-Nasution et al [17] showed there is only exist a narrow band of kinematics, for instance at Strouhal number ≈ 0.15 − 0.45 for heaving-pitching motion, where the wake remains two-dimensional and 2D force predictions are accurate. In this 2D range, the motion of the foil stabilize the spanwise-perturbed 3D structures found in the separated wake of a stationary foil, but 3D structures reappear when the amplitude of motion increases the shed vortex circulation above a 2D viscous stability limit.…”

Section: Introductionmentioning

confidence: 99%

Effects of aspect ratio on rolling and twisting foils

2021

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Flapping flight and swimming are increasingly studied both due to their intrinsic scientific richness and their applicability to novel robotic systems. Strip theory is often applied to flapping wings, but such modeling is only rigorously applicable in the limit of infinite aspect ratio (A) where the geometry and kinematics are effectively uniform. This work compares the flow features and forces of strip theory and three dimensional flapping foils, maintaining similitude in the rolling and twisting kinematics while varying the foil A. We find the key influence of finite A and spanwise varying kinematics is the generation of a time-periodic spanwise flow which stabilizes the vortex structures and enhances the dynamics at the foil root. An aspect-ratio correction for flapping foils is developed analogous to Prandtl finite wing theory, enabling future use of strip theory in analysis and design of finite aspect ratio flapping foils.

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Influence of three-dimensionality on propulsive flapping

Cited by 39 publications

References 32 publications

Deflected wake interaction of tandem flapping foils

Deflected wake interaction of tandem flapping foils

Fin sweep angle does not determine flapping propulsive performance

Effects of aspect ratio on rolling and twisting foils

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