Vortex formation and saturation for low-aspect-ratio rotating flat-plate fins

DeVoria, Adam C.; Ringuette, Matthew

doi:10.1007/s00348-011-1230-z

Cited by 66 publications

(30 citation statements)

References 70 publications

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“…We correct for this, as done by DeVoria & Ringuette (2012), by searching for any further grid points having ω z > ω z,th that are no greater than 2 √ 2 grid spacings from at least one point in the original cluster, and then appending them into the (augmented) set. Figure 6(a) shows a ω z field for A = 2 with a black contour indicating the originally identified cluster and a magenta contour showing the augmented cluster.…”

Section: Lev Circulation and Flow Fieldsmentioning

confidence: 99%

Aspect-ratio effects on rotating wings: circulation and forces

2015

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We employ experiments to study aspect ratio (A) effects on the vortex structure, circulation and lift force for flat-plate wings rotating from rest at 45 • angle of attack, which represents a simplified hovering-wing half-stroke. We use the time-varying, volumetric A = 2 data of Carr et al. (Exp. Fluids, vol. 54, 2013, pp. 1-26), reconstructed from phase-locked, phase-averaged stereoscopic digital particle image velocimetry (S-DPIV), and an A = 4 volumetric data set matching the span-based Reynolds number (Re) of A = 2. For A = 1-4 and Re span of O(10 3 -10 4 ), we directly measure the lift force. The total leading-edge-region circulation for A = 2 and 4 compares best overall using a span-based normalization and for matching rotation angles. The total circulation increases across the span to the tip region, and is larger for A = 2. After the startup, the total circulation for each A has a similar slope and a slow growth. The first leading-edge vortex (LEV) and the tip vortex (TV) for A = 4 move past the trailing edge, followed by substantial breakdown. For A = 2 the outboard, aft-tilted LEV merges with the TV and resides over the tip, although breakdown also occurs. Where the LEV is 'stable' inboard, its circulation saturates for A = 2 and the growth slows for A = 4. Aft LEV tilting reduces the spanwise LEV circulation for each A. Both positive and negative axial flow are found in the first LEV for A = 2 and 4, with the positive component being somewhat larger. This yields a generally positive (outboard) average vorticity flux. The average lift coefficient is essentially constant with A from 1 to 4 during the slow growth phase, although the large-time behaviour shows a slight decrease in lift coefficient with increasing A. The S-DPIV data are used to obtain the lift impulse and the spanwise and streamwise components contributing to the lift coefficient. The spanwise contribution is similar for A = 2 and 4, due to similar trailing-edge vortex interactions, LEV saturation behaviour and total circulation slopes. However, for A = 2 the streamwise contribution is much larger, because of the stronger, coherent TV and aft-tilted LEV, which will create a relatively lower-pressure region over the tip.

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Section: Lev Circulation and Flow Fieldsmentioning

confidence: 99%

Aspect-ratio effects on rotating wings: circulation and forces

2015

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“…Widmann and Tropea [75] have recently used experiments to investigate mechanisms responsible for the formation and detachment of LEVs. Other recent contributions characterizing 3D vortical structures on unsteady plates using high-fidelity simulations and experiments include those by Visbal et al [72], Devoria and Ringuette [15], Carr et al [9], Jones and Babinsky [32,33], Panah et al [53], and Bos et al [5].…”

Section: Introductionmentioning

confidence: 99%

Leading-edge flow criticality as a governing factor in leading-edge vortex initiation in unsteady airfoil flows

Ramesh

Granlund

et al. 2017

Theor. Comput. Fluid Dyn.

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A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil-Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements.

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“…Recent studies that focused exclusively on characterization of the LEV formation have used predefined kinematic motion of a sharp-edged flat plate to explore the forces induced by pitching (Granlund et al, 2013;Jantzen et al, 2014), rotation (DeVoria and Ringuette, 2012;Wojcik and Buchholz, 2014), and plunging (Rival et al, 2009;Ford and Babinsky, 2013). Numerous studies on pitching and/or plunging wings with sufficient forcing have identified reduced frequency as the primary scaling parameter that determines the flow evolution and unsteady force (see, e.g., Baik et al, 2012;Jantzen et al, 2014).…”

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confidence: 99%