Experimental observations of the three-dimensional wake structures and dynamics generated by a rigid, bioinspired pitching panel

King, Justin T.; Kumar, Rahul; Green, Melissa A.

doi:10.1103/physrevfluids.3.034701

Cited by 38 publications

(16 citation statements)

References 34 publications

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“…As the loop advects into the wake, its downstream end wraps around the upstream end of the previous loop, forming one of the spanwise vorticity cores of the 2S wake (vortex 2 in figure 6a). Similarly interconnected loops have been seen behind trapezoidal panels at comparable Reynolds numbers (King, Kumar & Green 2018) Near the ground, half of the von Kaŕmań vortices are slowed by the ground, causing the vortex street to clump into vortex pairs that mutually advect upward (figure 6b). These paired vortices were seen behind near-ground two-dimensional pitching foils (Quinn et al 2014a), and here we show how they fit into a larger three-dimensional wake.…”

Section: Near-ground Wakes Of High-and Low-aspect-ratio Foilsmentioning

confidence: 65%

Aspect ratio affects the equilibrium altitude of near-ground swimmers

et al. 2021

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Section: Near-ground Wakes Of High-and Low-aspect-ratio Foilsmentioning

confidence: 65%

Aspect ratio affects the equilibrium altitude of near-ground swimmers

et al. 2021

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“…Three studies that have addressed these issues to some extent are Green, Rowley & Smits (2011) and King, Kumar & Green (2018) who studied the behaviour of low aspect ratio trapezoidal panels with square trailing 874 P1-46 edges (an approximation to the truncate caudal fin shape), and Van Buren et al (2017a) who investigated foils with planforms that varied systematically from a shape that approximated a forked tail to that of a lanceolate tail. King et al (2018) focused primarily on the wake structure that develops downstream of the trapezoidal foil with increasing Strouhal number. Isometric views of the phase-averaged three-dimensional isosurfaces of Q are shown in figure 34, where the Q criterion proposed by Hunt, Wray & Moin (1988) helps to identify the vortex structure.…”

Section: Effects Of Planformmentioning

confidence: 99%

Undulatory and oscillatory swimming

Smits¹

2019

J. Fluid Mech.

201

113

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Theory and modelling remain central to improving our understanding of undulatory and oscillatory swimming. Simple models based on added mass can help to give great insight into the mechanics of undulatory swimming, as demonstrated by animals such as eels, stingrays and knifefish. To understand the swimming of oscillatory swimmers such as tuna and dolphins, models need to consider both added mass forces and circulatory forces. For all types of swimming, experiments and theory agree that the most important velocity scale is the characteristic lateral velocity of the tail motion rather than the swimming speed, which erases to a large extent the difference between results obtained in a tethered mode, compared to those obtained using a free swimming condition. There is no one-to-one connection between the integrated swimming performance and the details of the wake structure, in that similar levels of efficiency can occur with very different wake structures. Flexibility and viscous effects play crucial roles in determining the efficiency, and for isolated propulsors changing the profile shape can significantly improve both thrust and efficiency. Also, combined heave and pitch motions with an appropriate phase difference are essential to achieve high performance. Reducing the aspect ratio will always reduce thrust and efficiency, but its effects are now reasonably well understood. Planform shape can have an important mitigating influence, as do non-sinusoidal gaits and intermittent actuation.

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“…A few special cases outside these conditions were also simulated: A flipper-like motion using higher k * = 0.6 and St = 0.6 to imitate penguin and turtle swimming data with high roll and twist angles to maintain high propulsion and efficiency due to high . Also, a tail-like motion at lower amplitude A = 0.13 l * and much higher frequency at St = 0.46 inspired by recent robotics studies at similar operating conditions (28, 29).…”

Section: Introductionmentioning

confidence: 99%

“…A set of example simulation results for both tail-like and flipper-like motions are shown in Fig. 3, with the flow’s vortex structures visualized using the Q -criterion (29). The complete unsteady flow field evolution can be viewed in the supplementary video.…”

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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Experimental observations of the three-dimensional wake structures and dynamics generated by a rigid, bioinspired pitching panel

Cited by 38 publications

References 34 publications

Aspect ratio affects the equilibrium altitude of near-ground swimmers

Aspect ratio affects the equilibrium altitude of near-ground swimmers

Undulatory and oscillatory swimming

Fin sweep angle does not determine flapping propulsive performance

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