Effect of Airfoil Shape and Reynolds Number on Leading Edge Vortex Shedding in Unsteady Flows

Ramesh, Kiran; Ke, Jianghua; Gopalarathnam, Ashok; Edwards, Jack R.

doi:10.2514/6.2012-3025

Cited by 10 publications

(8 citation statements)

References 11 publications

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“…This variation was documented in Ref. 38 Figure 4. Since we are only examining the results until the point of LEV formation, the LEV shedding in the theoretical model is "turned off".…”

Section: Iiia1 Calibration Of Lesp Crit With Re Vmagmentioning

confidence: 94%

Theoretical Analysis of Perching and Hovering Maneuvers

Ramesh

Gopalarathnam

Edwards

et al. 2013

31st AIAA Applied Aerodynamics Conference

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“…This variation was documented in Ref. 38 Figure 4. Since we are only examining the results until the point of LEV formation, the LEV shedding in the theoretical model is "turned off".…”

Section: Iiia1 Calibration Of Lesp Crit With Re Vmagmentioning

confidence: 94%

Theoretical Analysis of Perching and Hovering Maneuvers

Ramesh

Gopalarathnam

Edwards

et al. 2013

31st AIAA Applied Aerodynamics Conference

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“…It is interesting, however, that the reduced frequency of response is nearly the same value and independent of critical LESP. In earlier research, Ramesh et al [51] have shown that airfoils with more rounded leading edges can support more suction, and hence have higher values of critical LESP. For example, a flat plate at Re = 1, 000 has LESP crit = 0.11, and a NACA0015 airfoil at the same Reynolds number has LESP crit = 0.19.…”

Section: Parametric Study D: Effect Of Change In Airfoil Shape (Lesp mentioning

confidence: 98%

Limit-cycle oscillations in unsteady flows dominated by intermittent leading-edge vortex shedding

Ramesh

Murua

Gopalarathnam

2015

Journal of Fluids and Structures

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High-frequency limit-cycle oscillations of an airfoil at low Reynolds number are studied numerically. This regime is characterized by large apparentmass effects and intermittent shedding of leading-edge vortices. Under these conditions, leading-edge vortex shedding has been shown to result in favorable consequences such as high lift and efficiencies in propulsion/power extraction, thus motivating this study. The aerodynamic model used in the aeroelastic framework is a potential-flow-based discrete-vortex method, augmented with intermittent leading-edge vortex shedding based on a leadingedge suction parameter reaching a critical value. This model has been validated extensively in the regime under consideration and is computationally cheap in comparison with Navier-Stokes solvers. The structural model used has degrees of freedom in pitch and plunge, and allows for large amplitudes and cubic stiffening. The aeroelastic framework developed in this paper is employed to undertake parametric studies which evaluate the impact of different types of nonlinearity. Structural configurations with pitch-to-plunge frequency ratios close to unity are considered, where the flutter speeds are lowest (ideal for power generation) and reduced frequencies are highest. The range of reduced frequencies studied is two to three times higher than most airfoil studies, a virtually unexplored regime. Aerodynamic nonlinearity re- * Corresponding authorEmail addresses: kiran.ramesh@glasgow.ac.uk (Kiran Ramesh), j.murua@surrey.ac.uk (Joseba Murua), agopalar@ncsu.edu (Ashok Gopalarathnam) Fluids and Structures February 10, 2015 sulting from intermittent leading-edge vortex shedding always causes a supercritical Hopf bifurcation, where limit-cycle oscillations occur at freestream velocities greater than the linear flutter speed. The variations in amplitude and frequency of limit-cycle oscillations as functions of aerodynamic and structural parameters are presented through the parametric studies. The excellent accuracy/cost balance offered by the methodology presented in this paper suggests that it could be successfully employed to investigate optimum setups for power harvesting in the low-Reynolds-number regime. Preprint submitted to Journal of

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“…The approximation of downward transport of vorticity, as employed in our study similar to that of Schnipper et al (2009), was based on estimating the vorticity production from Tietjens et al (1957), which does not account for any effect of splitting mechanism in the wake of bluff bodies. As also detailed in the study by Ramesh et al (2012), with regard to unsteady effects on leading edge vortex shedding with increasing Re, the vorticity distribution and thereby the circulation is inherently dependent on the wake-induced downwash velocity in parallel and normal 0.33T 0.45T 0.57T 0.69T 0.81T 0.93T directions to the foil chord. This wake-induced velocity at Re = 4000 will not be similar to the approximation (Ramesh et al 2012) that holds at Re = 1000 due to the onset of unsteady splitting mechanisms in the near wake.…”

Section: Formation Mechanism Of Rbvk + 2p Mode and Symmetric Bifurcat...mentioning

confidence: 85%

“…As also detailed in the study by Ramesh et al (2012), with regard to unsteady effects on leading edge vortex shedding with increasing Re, the vorticity distribution and thereby the circulation is inherently dependent on the wake-induced downwash velocity in parallel and normal 0.33T 0.45T 0.57T 0.69T 0.81T 0.93T directions to the foil chord. This wake-induced velocity at Re = 4000 will not be similar to the approximation (Ramesh et al 2012) that holds at Re = 1000 due to the onset of unsteady splitting mechanisms in the near wake. This attributes directly to the inaccuracy in estimating circulation of the leading edge, or boundary layer, vortices (i.e.…”

Section: Formation Mechanism Of Rbvk + 2p Mode and Symmetric Bifurcat...mentioning

confidence: 85%

Characterization of bifurcated dual vortex streets in the wake of an oscillating foil

Verma

Hemmati

2022

J. Fluid Mech.

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Wake evolution of an oscillating foil with combined heaving and pitching motion is evaluated numerically for a range of phase offsets ( $\phi$ ), chord-based Strouhal numbers ( $St_c$ ) and Reynolds numbers ( $Re$ ). The increase in $\phi$ from $90^\circ$ to $180^\circ$ at a given $St_c$ and $Re$ coincides with a transition of pitch- to heave-dominated kinematics that further reveals novel transitions in wake topology characterized by bifurcated vortex streets. At $Re= 1000$ , each of the dual streets constitutes a dipole-like paired configuration of counter-rotating coherent structures that resemble qualitatively the formation of $2P$ mode. A new mathematical relation between the relative circulation of coherent dipole-like paired structures and kinematic parameters is proposed, including heave-based ( $St_h$ ), pitch-based ( $St_{\theta }$ ) and combined motion ( $St_A$ ) Strouhal numbers, as well as $\phi$ . This model can predict accurately the wake transition towards $2P$ mode characterized by a bifurcation, at low $Re= 1000$ . At $Re= 4000$ , however, the relationship was inaccurate in predicting the wake transition. A shear splitting process is observed at $Re= 4000$ , which leads to the formation of reverse Bénard–von Kármán mode in conjunction with $2P$ mode. Increasing $\phi$ further depicts a consistent prolongation of the splitting process, which coincides with a unique transition in terms of absence and reappearance of bifurcated dipole-like pairs at $\phi = 120^\circ$ and $180^\circ$ , respectively. Changes in the spatial arrangement of $2P$ pairs observed consistently for oscillating foils with the combined motion constitute a novel wake transition that becomes more dominant at higher Reynolds numbers.

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Effect of Airfoil Shape and Reynolds Number on Leading Edge Vortex Shedding in Unsteady Flows

Cited by 10 publications

References 11 publications

Theoretical Analysis of Perching and Hovering Maneuvers

Theoretical Analysis of Perching and Hovering Maneuvers

Limit-cycle oscillations in unsteady flows dominated by intermittent leading-edge vortex shedding

Characterization of bifurcated dual vortex streets in the wake of an oscillating foil

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