Propulsive performance of unsteady tandem hydrofoils in an in-line configuration

Stogin, Birgitt Boschitsch; Dewey, Peter A.; Smits, Alexander J.

doi:10.1063/1.4872308

Cited by 162 publications

(141 citation statements)

References 27 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: 83%

“…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%

“…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%

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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: 83%

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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“…These results differ from the ones in [57]. In the experiments presented in [57], both the hydrofoils in the inline configuration are pitching, while in the work presented here, the leading hydrofoil is stationary. This leads to 2 major differences:…”

Section: System Advantages and Limitationscontrasting

confidence: 55%

“…However, in both these studies [57] [58] both the foils were pitching. Drawing on inspiration from the above, this study attempts to answer the question as to whether the placement of a stationary hydrofoil in front of a pitching hydrofoil offers any advantage in terms of speed/thrust, work done and economy/efficiency.…”

Section: Neutral Positionmentioning

confidence: 99%

Experimental Investigation Into the Effect of a Stationary Dorsal Fin for Multiple Configurations - A Bio-Inspired Perspective

Saraiya

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Results of experiments aimed at determining the performance of two quasi-two-dimensional hydrofoils arranged in an in-line configuration are presented. This thesis aims at understanding the role of pitching motion of a caudal fin in the presence of a dorsal fin, decoupled from heaving motion. A simplified model has been proposed, which accounts for pitching motion, and explores the role of frequency, amplitude, and separation distance between dorsal and caudal fins. The net thrust generated and the work done by the 2-fin model while undergoing prescribed pitching motions were calculated.The pitch experiments focus on four parameters to quantify their influence on propulsive performance; (1) frequency, (2) trailing edge amplitude, (3) separation between foils, and (4) flexibility of the fins. The experiments are conducted under both accelerating and free swimming conditions. It is hypothesized that distance of separation between the static dorsal and pitching caudal fins during free swimming will affect the work done and economy across amplitudes and frequencies due to the weakening of the wake from the leading hydrofoil. It is also expected that the change in flexibility at free-swimming speeds will cause a change in economy, and that the presence of the dorsal fin will amplify this effect. Finally, the thrust is hypothesized to follow trends similar to that of a pitching hydrofoil in terms of amplitude and frequency.While the increased drag due to the additional hydrofoil reduces the speed of motion, it also reduces the required work to move the lagging hydrofoil. The reduction in speed is ~10%, ii while the required work decreases by >20% on average, leading to an increase in economy.The effects increase with increasing amplitude and frequency during acceleration. As the distance between the hydrofoils is increased the efficiency and economy of the model reduces. Finally, flexible foils are more efficient in the presence of a stationary fin only at high frequencies and amplitudes.This study is a valuable preliminary work towards the evolution of design of bio-inspired models and possibly vehicles.A secondary aim of this thesis is the development of an inexpensive PIV technique to quantify flow fields. A PIV setup has been designed and built that allows the quantification of flows at speeds below 25.4 cm/s. At greater speeds, error margins exceed 10%.iii

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Generalization of waving‐plate theory to multiple interacting swimmers

Baddoo

Moore

Oza

et al. 2023

Comm Pure Appl Math

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Early research in aerodynamics and biological propulsion was dramatically advanced by the analytical solutions of Theodorsen, von Kármán, Wu and others. While these classical solutions apply only to isolated swimmers, the flow interactions between multiple swimmers are relevant to many practical applications, including the schooling and flocking of animal collectives. In this work, we derive a class of solutions that describe the hydrodynamic interactions between an arbitrary number of swimmers in a two‐dimensional inviscid fluid. Our approach is rooted in multiply‐connected complex analysis and exploits several recent results. Specifically, the transcendental (Schottky–Klein) prime function serves as the basic building block to construct the appropriate conformal maps and leading‐edge‐suction functions, which allows us to solve the modified Schwarz problem that arises. As such, our solutions generalize classical thin aerofoil theory, specifically Wu's waving‐plate analysis, to the case of multiple swimmers. For the case of a pair of interacting swimmers, we develop an efficient numerical implementation that allows rapid computations of the forces on each swimmer. We investigate flow‐mediated equilibria and find excellent agreement between our new solutions and previously reported experimental results. Our solutions recover and unify disparate results in the literature, thereby opening the door for future studies into the interactions between multiple swimmers.

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Propulsive performance of unsteady tandem hydrofoils in an in-line configuration

Cited by 162 publications

References 27 publications

Performance augmentation mechanism of in-line tandem flapping foils

Performance augmentation mechanism of in-line tandem flapping foils

Experimental Investigation Into the Effect of a Stationary Dorsal Fin for Multiple Configurations - A Bio-Inspired Perspective

Generalization of waving‐plate theory to multiple interacting swimmers

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