A criterion for vortex separation on unsteady aerodynamic profiles

Rival, David E.; Kriegseis, Jochen; Schaub, Pascal; Widmann, Alexander; Tropea, Cameron

doi:10.2514/6.2013-836

Cited by 15 publications

(21 citation statements)

References 18 publications

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“…Rival et al (2013) defined the occurrence of LEV detachment as the instant at which the rear stagnation point arrives at the trailing edge, since after its arrival, vortices that are generated from the trailing edge are rapidly fed to cut off the LEV and limit its growth. Figure 10 plots the stagnation points at the upper surface of the airfoil for k = 0.25, 0.5, 0.78 and 1.26 at α = 15…”

Section: Lev Growth and Detachmentmentioning

confidence: 99%

“…Vorticity values are measured at the upper surface, and the reattachment point is assumed to occur at the position where the vorticity changes from positive to negative (Rival et al 2013). Although this is not a rigorous definition of a reattachment point for the unsteady flow, the reattachment point is evolving slowly enough such that the stagnation points evaluated by the instantaneous vorticity field can provide useful information about the regions where the flow converges or diverges.…”

Section: Lev Growth and Detachmentmentioning

confidence: 99%

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Surging and plunging oscillations of an airfoil at low Reynolds number

2014

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We investigate the forces and unsteady flow structures associated with harmonic oscillations of an airfoil in the streamwise (surging) and transverse (plunging) directions in two-dimensional simulations at low Reynolds number. For the surging case, we show that there are specific frequencies where the wake instability synchronizes with the unsteady motion of the airfoil, leading to significant changes in the mean forces. Resonant behaviour of the time-averaged forces is observed near the vortex shedding frequency and its subharmonic; the behaviour is reminiscent of the dynamics of the generic nonlinear oscillator known as the Arnol'd tongue or the resonance horn. Below the wake instability frequency, there are two regimes where the fluctuating forces are amplified and attenuated, respectively. A detailed study of the flow structures associated with leading-edge vortex (LEV) growth and detachment are used to relate this behaviour with the LEV acting either in phase with the quasi-steady component of the forces for the amplification case, or out of phase for the attenuation case. Comparisons with wind tunnel measurements show that phenomenologically similar dynamics occur at higher Reynolds number. Finally, we show that qualitatively similar phenomena occur during both surging and plunging.

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Section: Lev Growth and Detachmentmentioning

confidence: 99%

Section: Lev Growth and Detachmentmentioning

confidence: 99%

Surging and plunging oscillations of an airfoil at low Reynolds number

2014

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“…This can be seen at a temporal location of 4 chords traveled where the 0.25T case has the least well-developed LEV and TEV. A potential explanation for this phenomenon is given by Rival et al [12].The authors investigated the effects of leading edge shape on the formation and separation of the LEV on a plunging airfoil, but what was found was that formation and detachment of the LEV was dominated by the shape of the trailing edge and not the leading edge. Similar to this paper the authors of [12] found that wing upper surfaces that were flatter had greater influence on the reverse shear layer and thus (comparatively) accelerate the evolution of the flowfield.…”

Section: Resultsmentioning

confidence: 96%

Analysis of a Variable Camber Wing during Highly Unsteady Maneuvers

Lego

Altman

2013

31st AIAA Applied Aerodynamics Conference

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Much is known about the effects of varying camber on lift and drag performance in fixed wings but little is known about the effects of varying camber during unsteady motions. Using a 2D Discrete Vortex Method (DVM) variable camber was studied for pitching and hold motions. These motions were selected as abstractions of a simple perching maneuver. Results show that varying the camber effects the formation of the LEV and causes temporal shifts in the force histories. These changes positively affect the operational envelope of any candidate air vehicle application. This increase in performance and expansion of the flight envelope could be highly beneficial to perching where such an expansion in the aerodynamic characteristics of a given configuration could be a requisite precondition to a successful perching maneuver.

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“…Since the bluff body detachment mechanism is characterized by the reattachment point of the LEV arriving at the trailing edge, some studies have demonstrated success in using the chord length to scale the circulation of an LEV [92,52]. However, Widmann…”

Section: Lev Scalingmentioning

confidence: 99%

“…Cleaver et al [27] Rival et al [92] also studied the effect of airfoil shape on the evolution of the flow field, and they too demonstrated that the shape of the leading edge had a noticeable effect on the initial separation of the LEV. However, they went on to show that the growth rate of the LEV was not strongly affected by airfoil shape, thereby characterizing why the vorticity fields remained similar.…”

Section: Effect Of Cross-sectional Shape Of An Airfoilmentioning

confidence: 99%

Understanding and controlling vorticity transport in unsteady, separated flows

Akkala¹

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A criterion for vortex separation on unsteady aerodynamic profiles

Cited by 15 publications

References 18 publications

Surging and plunging oscillations of an airfoil at low Reynolds number

Surging and plunging oscillations of an airfoil at low Reynolds number

Analysis of a Variable Camber Wing during Highly Unsteady Maneuvers

Understanding and controlling vorticity transport in unsteady, separated flows

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