Leading-Edge Vortices: Mechanics and Modeling

Eldredge, Jeff D.; Jones, Anya R.

doi:10.1146/annurev-fluid-010518-040334

Cited by 262 publications

(162 citation statements)

References 104 publications

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“…Comprehensive reviews of this phenomenon in the context of helicopter rotor blades and pitching airfoils are provided by [1][2][3][4]. For the case of flapping wings, as well as for severe impinging gusts, highly unsteady forcing induces the formation of dynamic stall including a leading-edge vortex [5]. The evolution and interaction of such vortical structures with the aerodynamic surfaces have a significant impact on flight stability and performance.…”

Section: Introductionmentioning

confidence: 99%

Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

Ramos

Wolf²,

Yeh

et al. 2019

Phys. Rev. Fluids

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High-fidelity simulations are performed to study active flow control techniques for alleviating deep dynamic stall of a SD7003 airfoil in plunging motion. The flow Reynolds number is Re = 60,000 and the freestream Mach number is M = 0.1. Numerical simulations are performed with a finite difference based solver that incorporates high-order compact schemes for differentiation, interpolation and filtering on a staggered grid. A mesh convergence study is conducted and results show good agreement with available data in terms of aerodynamic coefficients. Different spanwise arrangements of actuators are implemented to simulate blowing and suction at the airfoil leading edge. We observe that, for a specific frequency range of actuation, mean drag and drag fluctuations are substantially reduced while mean lift is maintained almost unaffected, especially for a 2D actuator setup. For this frequency range, 2D flow actuation disrupts the formation of the dynamic stall vortex, what leads to drag reduction due to a pressure increase along the airfoil suction side, towards the trailing edge region. At the same time, pressure is reduced on the suction side near the leading edge, increasing lift and further reducing drag.

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Section: Introductionmentioning

confidence: 99%

Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

Ramos

Wolf²,

Yeh

et al. 2019

Phys. Rev. Fluids

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“…Of related interest has been the burgeoning field of controlled analogs of those gusts or simple transients to provide understanding for more complex realistic flows. Examples are the study of airfoil response to maneuvers such as pitching, plunging, and/or surging, as reviewed in, e.g., [6]. In each of these cases, goals include a broader understanding of the time scales and force magnitudes associated with unsteady flow development and, of primary importance to this study, improved aerodynamic performance under periodic vortex passage and random gust encounters.…”

Section: Introductionmentioning

confidence: 99%

Vortical Gusts: Experimental Generation and Interaction with Wing

Hufstedler

McKeon

2019

AIAA Journal

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We describe the experimental generation of isolated vortical gusts and the interaction between these gusts and a downstream airfoil at a Reynolds number of 20,000. A standard method of generating a vortical gust has been to rapidly pitch an airfoil. A different approach is presented here: heaving a plate across a tunnel and changing direction rapidly to release a vortex. This method is motivated by the desire to limit a test article's exposure to the wake of the gust generator by moving it to the side of the tunnel. Two suites of experiments were performed to characterize the performance of the gust generators and to measure the forces on and flow around the downstream airfoil. The novel mechanism allowed for measurement of the resumption of vortex shedding from the downstream airfoil, which was impossible with the pitching generator. Nomenclature C L = lift coefficient, lift/(dynamic pressure × wing area) c a = airfoil chord length, m c p = plate chord length, m h = plate heave distance, m Re c = Reynolds number with respect to airfoil's chord length S = heaving speed ratio, V heave ∕U T = heaving time ratio, t heave ∕t cp t = time, s t a = normalized plate acceleration time, t accel ∕t cp t accel = plate acceleration time, s t c = chordwise convective time across airfoil, s t cp = chordwise convective time across plate, s t heave = heaving time, s t p = normalized airfoil pitching time, t pitch ∕t c t pitch = generator pitching time, s U = freestream speed, m∕s u = velocity in x direction, m∕s V heave = plate heaving speed, m∕s v = velocity in y direction, m∕s x = streamwise coordinate, m x 0 = streamwise position computed from unwrapping process, m y = cross-stream coordinate with respect to tunnel midline, m y 0 = initial plate distance from midline, m y peak = cross-stream position of maximum displacement of heaving plate, m y plate = cross-stream position of heaving plate, m y upstream = cross-stream position of pitching gust generator, m z = spanwise coordinate, m α = angle of attack of test article, rad (unless otherwise noted) α 1 = initial angle of pitching gust generator, rad (unless otherwise noted) α 2 = final angle of pitching gust generator, rad (unless otherwise noted) α eff = effective angle of attack of heaving gust generator, rad (unless otherwise noted) α upstream = angle of attack of pitching gust generator, rad (unless otherwise noted) Γ v = circulation of shed vortex, m 2 ∕s Γ v;est;heave = estimated circulation of shed vortex from heaving generator, m 2 ∕s Γ v;est;pitch = estimated circulation of shed vortex from pitching generator, m 2 ∕s Γ 2 = vortex identification criterion Δx = streamwise distance between generator and test article, m τ a = normalized time, t∕t c ω z = vorticity measured in x-y plane, s −1

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“…Around the same time, in 2004, evidence of LEV on bird wings was also provided ( Figure 1b, Videler et al, 2004) suggesting lift enhancement. This seminal work on insect and bird flight led to significant studies of the LEV on oscillating and revolving wings ( Figure 1c, Taira & Colonius, 2009) and has been of paramount importance to understand the different stabilization mechanisms that allow a vortex to remain stably ('trapped') near a wing (Eldredge & Jones, 2019). In the case of spinnakers (Figure 1d), the LEV has similarities with that of bird wings ( Figure 1b) and translating wings ( Figure 1c) due to the comparable sweepback angle and strong interaction with the tip vortex.…”

Section: Leading Edge Flowmentioning

confidence: 99%

Recent Advances in Numerical and Experimental Downwind Sail Aerodynamics

Souppez

Arredondo-Galeana

Viola

2019

Journal of Sailing Technology

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Over the past two decades, the numerical and experimental progresses made in the field of downwind sail aerodynamics have contributed to a new understanding of their behaviour and improved designs. Contemporary advances include the numerical and experimental evidence of the leading-edge vortex, as well as greater correlation between model and full-scale testing. Nevertheless, much remains to be understood on the aerodynamics of downwind sails and their flow structures. In this paper, a detailed review of the different flow features of downwind sails, including the effect of separation bubbles and leading-edge vortices will be discussed. New experimental measurements of the flow field around a highly cambered thin circular arc geometry, representative of a bi-dimensional section of a spinnaker, will also be presented here for the first time. These results allow interpretation of some inconsistent data from past experiments and simulations, and to provide guidance for future model testing and sail design.

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Leading-Edge Vortices: Mechanics and Modeling

Cited by 262 publications

References 104 publications

Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

Vortical Gusts: Experimental Generation and Interaction with Wing

Recent Advances in Numerical and Experimental Downwind Sail Aerodynamics

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