Numerical simulations of the flow around a square pitching panel

Şentürk, Utku; Smits, Alexander J.

doi:10.1016/j.jfluidstructs.2017.11.001

Cited by 29 publications

(37 citation statements)

References 27 publications

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“…As anticipated, the vortex structures form a bifurcating wake consisting of two vortex rings per oscillation cycle that propagate downstream and away from the Y * = 0 plane. This type of bifurcating wake has been reported in previous studies of low-aspect ratio flat plate experiments [36] and simulations [39], and of low-aspect ratio ellipsoidal wing simulations [37]. Figure 5 shows the xand y-components of the time-averaged velocity field normalized with the free-stream velocity, u * = u/U, and v * = v/U, respectively.…”

Section: Isolated Hydrofoil Performance and Wake Measurementssupporting

confidence: 78%

“…Similarly, Dong et al [37] conducted a series of numerical simulations to investigate the effect of aspect ratio on the wake topology and propulsive performance of thin ellipsoidal flapping hydrofoils for Strouhal numbers up to 1.2, and they found a similar wake topology for an A = 1.27 hydrofoil operating at St ≥ 0.4. Yet again, a bifurcating wake is observed for combined heaving and pitching hydrofoils of A = 3 at St = 0.4 [38], and square pitching panels (A = 1) at St = 0.4 [39]. Schematics of two different wake topologies behind a finite-span pitching hydrofoil where (a) vortex rings bifurcate away from each other in the cross-stream direction as they advect downstream, commonly seen in eel-like swimming, and (b) interconnected vortex rings advect downstream, commonly seen in fish-like swimming.…”

Section: Introductionmentioning

confidence: 86%

hydrofoil operating at

. Yet again, a bifurcating wake is observed for combined heaving and pitching hydrofoils of

[ 38 ], and square pitching panels (

) at

[ 39 ].…”

Section: Introductionmentioning

confidence: 99%

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Flow Interactions Between Low Aspect Ratio Hydrofoils in In-line and Staggered Arrangements

2020

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Many species of fish gather in dense collectives or schools where there are significant flow interactions from their shed wakes. Commonly, these swimmers shed a classic reverse von Kármán wake, however, schooling eels produce a bifurcated wake topology with two vortex rings shed per oscillation cycle. To examine the schooling interactions of a hydrofoil with a bifurcated wake topology, we present tomographic particle image velocimetry (tomo PIV) measurements of the flow interactions and direct force measurements of the performance of two low-aspect-ratio hydrofoils ( A R = 0.5 ) in an in-line and a staggered arrangement. Surprisingly, when the leader and follower are interacting in either arrangement there are only minor alterations to the flowfields beyond the superposition of the flowfields produced by the isolated leader and follower. Motivated by this finding, Garrick’s linear theory, a linear unsteady hydrofoil theory based on a potential flow assumption, was adapted to predict the lift and thrust performance of the follower. Here, the follower hydrofoil interacting with the leader’s wake is considered as the superposition of an isolated pitching foil with a time-varying cross-stream velocity derived from the wake flow measurements of the isolated leader. Linear theory predictions accurately capture the time-averaged lift force and some of the major peaks in thrust derived from the follower interacting with the leader’s wake in a staggered arrangement. The thrust peaks that are not predicted by linear theory are likely driven by spatial variations in the flowfield acting on the follower or nonlinear flow interactions; neither of which are accounted for in the simple theory. This suggests that unsteady potential flow theory that does account for spatial variations in the flowfield acting on a hydrofoil can provide a relatively simple framework to understand and model the flow interactions that occur in schooling fish. Additionally, schooling eels can derive thrust and efficiency increases of 63-80% in either a in-line or a staggered arrangement where the follower is between two branched momentum jets or with one momentum jet branch directly impinging on it, respectively.

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Section: Isolated Hydrofoil Performance and Wake Measurementssupporting

confidence: 78%

Section: Introductionmentioning

confidence: 86%

hydrofoil operating at

. Yet again, a bifurcating wake is observed for combined heaving and pitching hydrofoils of

[ 38 ], and square pitching panels (

) at

[ 39 ].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Flow Interactions Between Low Aspect Ratio Hydrofoils in In-line and Staggered Arrangements

2020

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“…There is no heaving motion. The results for the thrust, power and efficiency shown in figure 13 were computed using the direct numerical simulations (DNS) method described by Sentürk & Smits (2018) and . The Reynolds number was varied from 500 to 32 000.…”

Section: Pitching Foilsmentioning

confidence: 99%

Undulatory and oscillatory swimming

Smits¹

2019

J. Fluid Mech.

Self Cite

182

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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“…Firstly, the pore would attenuate the magnitude of the large scale eddies in the trailing wake, due to the high frequency communication disrupting the large amplitude eddies rolling off the trailing edge. Secondly, the presence of the pore in the primary thrust generating region of 0.625C-0.75C would have a significant reduction in thrust generation [6]. There are many variables affecting the physics of pitching plates.…”

Section: Introductionmentioning

confidence: 99%

Effects of Geometric Porosity in the Trailing Edge of a Flexible Pitching Plate

Hanrahan¹,

Joshi²,

Jaiman³

2020

Australasian Fluid Mechanics Conference (AFMC)

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While pitching and heaving plates have been studied extensively, the effects of geometry have only recently gained interest in the research community. Inspired by porosity present in avian feathers, this numerical investigation assesses the effects of geometric porosity on a flexible pitching plate and quantifies the effect of a geometric pore of diameter 0.07C, that transitions along the centre-line between 0.725C and 0.925C. The pore forms small and periodic secondary hairpin structures in the trailing wake, having a significant effect on the propulsive efficiency (η) at lower Strouhal numbers (St). The thrust coefficient (C t ) decreases due to the effects of the pore, and the power coefficient (C Pow ) is considered invariant to the presence of the pore. Optimised geometric pores may be useful in bio-inspired micro air vehicle applications, as well as wind and ocean engineering.

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Numerical simulations of the flow around a square pitching panel

Cited by 29 publications

References 27 publications

Flow Interactions Between Low Aspect Ratio Hydrofoils in In-line and Staggered Arrangements

Flow Interactions Between Low Aspect Ratio Hydrofoils in In-line and Staggered Arrangements

Undulatory and oscillatory swimming

Effects of Geometric Porosity in the Trailing Edge of a Flexible Pitching Plate

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