Vorticity transport and the leading-edge vortex of a plunging airfoil

Panah, Azar Eslam; Akkala, James; Buchholz, James

doi:10.1007/s00348-015-2014-7

Cited by 36 publications

(28 citation statements)

References 47 publications

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“…They term this locally initiated detachment mechanism 'boundary-layer eruption', which adopts the terminology used by Doligalski et al (1994). This kind of detachment without recirculation of fluid around the trailing edge, where c is not the characteristic length scale, was also observed by Eslam Panah et al (2015) and Akkala and Buchholz (2017) for an LEV on a plunging flat plate at high k between 1 and 2.…”

Section: Introductionsupporting

confidence: 68%

Insights into leading edge vortex formation and detachment on a pitching and plunging flat plate

Kissing

Kriegseis

et al. 2020

Exp Fluids

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The present study is a prelude to applying different flow control devices on pitching and plunging airfoils with the intention of controlling the growth of the leading edge vortex (LEV); hence, the lift under unsteady stall conditions. As a pre-requisite the parameters influencing the development of the LEV topology must be fully understood and this constitutes the main motivation of the present experimental investigation. The aims of this study are twofold. First, an approach is introduced to validate the comparability between flow fields and LEV characteristics of two different facilities using water and air as working media by making use of a common baseline case. The motivation behind this comparison is that with two facilities the overall parameter range can be significantly expanded. This comparison includes an overview of the respective parameter ranges, control of the airfoil kinematics and careful scrutiny of how post-processing procedures of velocity data from time-resolved particle image velocimetry (PIV) influence the integral properties and topological features used to characterise the LEV development. Second, and based on results coming from both facilities, the appearance of secondary structures and their effect on LEV detachment over an extended parameter range is studied. A Lagrangian flow field analysis based on finite-time Lyapunov Exponent (FTLE) ridges allows precise identification of secondary structures and reveals that their emergence is closely correlated to a vortex Reynolds number threshold computed from the LEV circulation. This threshold is used to model the temporal onset of secondary structures. Further analysis indicates that the emergence of secondary structures causes the LEV to stop accumulating circulation if the shear layer angle at the leading edge of the flat plate has ceased to increase. This information is of particular importance for advanced flow control applications, since efforts to strengthen and/or prolong LEV growth rely on precise knowledge about where and when to apply flow control measures. Graphical abstract

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Section: Introductionsupporting

confidence: 68%

Insights into leading edge vortex formation and detachment on a pitching and plunging flat plate

Kissing

Kriegseis

et al. 2020

Exp Fluids

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“…Taira & Colonius (2009), Hartloper & Rival (2013)), swept wings (see e.g. Wong & Rival (2015)) and the interaction of the vortex with secondary boundary layers (Eslam Panah, Akkala & Buchholz 2015;Akkala & Buchholz 2017).…”

Section: Introductionmentioning

confidence: 99%

The influence of edge undulation on vortex formation for low-aspect-ratio propulsors

2019

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“…For a controlled growth of a LEV, Ford and Babinsky [15] investigated the unsteady vortex formation on an accelerating flat plate, finding that most of the bound circulation remained in the LEV. Also interested in vorticity transport, Panah et al [16] calculated the circulation during the LEV development on a plunging foil at a modest Reyolds number of 10, 000.…”

Section: Introductionmentioning

confidence: 99%

Unsteady high-lift mechanisms from heaving flat plate simulations

Franck

Breuer

2017

International Journal of Heat and Fluid Flow

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Flapping animal flight is often modeled as a combined pitching and heaving motion in order to investigate the unsteady flow structures and resulting forces that could augment the animal's lift and propulsive capabilities. This work isolates the heaving motion of flapping flight in order to numerically investigate the flow physics at a Reynolds number of 40,000, a regime typical for large birds and bats and challenging to simulate due to the added complexity of laminar to turbulent transition in which boundary layer separation and reattachment are traditionally more difficult to predict. Periodic heaving of a thin flat plate at fixed angles of attacks of 1, 5, 9, 13, and 18 degrees are simulated using a large-eddy simulation (LES). The heaving motion significantly increases the average lift compared with the steady flow, and also surpasses the quasi-steady predictions due to the formation of a leading edge vortex (LEV) that persists well into the static stall region. The progression of the high-lift mechanisms throughout the heaving cycle is presented over the range of angles of attack. Lift enhancement compared with the equivalent steady state flow was found to be up to 17% greater, and up to 24% greater than that predicted by a quasi-steady analysis. For the range of kinematics explored it is found that maximum lift enhancement occurs at an angle of attack of 13 degrees, with a maximum lift coefficient of 2.1, a mean lift coefficient of 1.04.

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Vorticity transport and the leading-edge vortex of a plunging airfoil

Cited by 36 publications

References 47 publications

Insights into leading edge vortex formation and detachment on a pitching and plunging flat plate

Insights into leading edge vortex formation and detachment on a pitching and plunging flat plate

The influence of edge undulation on vortex formation for low-aspect-ratio propulsors

Unsteady high-lift mechanisms from heaving flat plate simulations

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