Vortex formation on a pitching aerofoil at high surging amplitudes

Smith, Llewellyn; Jones, Anya R.

doi:10.1017/jfm.2020.741

Cited by 11 publications

(7 citation statements)

References 43 publications

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“…Flow field assessments indicate that these differences are likely due to LEV and trailing-edge vortex interactions, and reduced frequency has a profound impact on this behavior. For wings in large streamwise oscillations where flow fully reverses on the wing, the onset of vortex formation appears to be insensitive to the reduced frequency for 0.1 ≤ k ≤ 0.3, where reduced frequency does not play a large role in the development of the near wake (Smith & Jones 2020). A scaling analysis suggests that unsteady boundary layer effects are not likely to affect vortex formation for k < O(1).…”

Section: Streamwise Gustsmentioning

confidence: 92%

Physics and Modeling of Large Flow Disturbances: Discrete Gust Encounters for Modern Air Vehicles

Jones

Çeti̇ner

Smith

2022

Annu. Rev. Fluid Mech.

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Gusts of moderate and large magnitude induce flow separation and other complexities when they interact with the lifting surfaces of air vehicles. The presence of these nonlinear gusts are becoming ubiquitous in twenty-first-century air vehicles, where the classic potential flow–based methodologies applied in the past may no longer be valid. In this review, we define the parameter space for the presence of large-amplitude gusts and describe where and when these gusts may primarily be found. Recent research using modern experimental and computational techniques to define the limits of classical unsteady and indicial aerodynamic theories is summarized, with a focus on discrete transverse, streamwise (longitudinal), and vortex gust encounters. We propose areas where future research is needed to transition these studies of large-amplitude gust physics to real-time prediction and mitigation during flight. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Section: Streamwise Gustsmentioning

confidence: 92%

Physics and Modeling of Large Flow Disturbances: Discrete Gust Encounters for Modern Air Vehicles

Jones

Çeti̇ner

Smith

2022

Annu. Rev. Fluid Mech.

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“…Gendrich [16] suggests the definition of an unsteady separation point on the basis of the boundary layer thickness (𝛿), displacement thickness ( 𝛿 * ) or momentum thickness (𝜃) relative to their initial values. Smith and Jones [17] proposed a Falkner-Skan parameter (𝛽) as a criterion for LEV shedding. We take note of the fact that a quantity that is often associated with separation (in steady laminar flows at least) is the shape factor, H = 𝛿 * 𝜃 .…”

Section: Introductionmentioning

confidence: 99%

Prediction of Vortex Initiation using an Unsteady Panel Method with an Integral-Boundary-Layer Calculation

Ramanathan

Gopalarathnam

2022

AIAA AVIATION 2022 Forum

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In our current work, we implement and evaluate the efficacy of a boundary layer parameter (𝐻 32 ) based low-order model to signal the onset of leading-edge vortex (LEV) initiation for low Re flows (O (10 4 )) . In an earlier work(AIAA Aviation Forum 2019, p.3590) using numerical simulations, it was proven that the shape factor parameter (𝐻 32 ) attains a critical value of ∼ 1.52 prior to the formation of dynamic stall vortex (DSV) irrespective of airfoil, motion kinematics. Numerical simulations spanned high pitch rate motions (𝐾 ≥ 0.1) and three leading edge radii (0.5 ≤ 𝑟 𝐿𝐸 ≤ 2.0) for three different pivot locations : leading-edge (LE), quarter-chord (QC) and half-chord (HC). This finding concurred with the 𝐻 32 value reported in literature for laminar separation (𝐻 32 = 1.515) in steady incompressible flows. In the second part of the effort, we focus on low-order prediction of LEV initiation using this criticality. This was achieved using an inviscid calculation of unsteady-airfoil velocity and pressure distributions, which serve as an input to a quasi-steady integral boundary layer (IBL) method. The results provided here demonstrate the effectiveness of 𝐻 32 in predicting leading-edge flow reversal. We show, by analysing different cases, that this inexpensive method has crucial ramifications in picking the appropriate 𝐿𝐸 𝑆𝑃 𝑐𝑟𝑖𝑡 for any given airfoil and motion combination. Hence, we eliminate the need for CFD, Experiments to obtain 𝐿𝐸 𝑆𝑃 𝑐𝑟𝑖𝑡 for a new parameter set.

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“…Furthermore, by performing the experiments over a pitching delta wing, Shi and Ming [23] elaborated the mechanism of the maximal lift increase and dynamic stall angle delay, which is ascribed to the change of the leading-edge vortex structure. Recently, to study the evolution of the leading-edge vortex and boundary layer unsteadiness, the experiments were done in a wide range of freestream oscillating amplitudes and reduced frequencies by Smith and Jones [24]. Simultaneously, the vortex formation over the reversed airfoil under freestream oscillating condition was investigated by Kirk and Jones [25] experimentally and main results include the higher convection speed and comparable strength of LEVs in reverse flow surge compared with the reverse flow LEVs.…”

Section: Effect Of Time-varying Freestream On Performance and Vortex ...mentioning

confidence: 99%

Effect of time-varying freestream on performance and vortex dynamics of forward and reversed pitching airfoils

Shi

Wang

Bayeul-Lainé

et al. 2022

Journal of Fluids and Structures

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Vortex formation on a pitching aerofoil at high surging amplitudes

Abstract: Abstract

Cited by 11 publications

References 43 publications

Physics and Modeling of Large Flow Disturbances: Discrete Gust Encounters for Modern Air Vehicles

Physics and Modeling of Large Flow Disturbances: Discrete Gust Encounters for Modern Air Vehicles

Prediction of Vortex Initiation using an Unsteady Panel Method with an Integral-Boundary-Layer Calculation

Effect of time-varying freestream on performance and vortex dynamics of forward and reversed pitching airfoils

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