Vortex Formation and Saturation for Low-Aspect-Ratio Rotating Flat Plates at Low Reynolds Number

DeVoria, Adam C.; Mahajan, Priyanka; Ringuette, Matthew

doi:10.2514/6.2011-396

Cited by 24 publications

(25 citation statements)

References 57 publications

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“…Similarly, Visbal (2009) observed significantly enhanced entrainment of this wall layer on a plunging airfoil when the leading-edge shear layer was transitional. This is a variant of the classical problem of a vortex interacting with a wall (Doligalski, Smith & Walker 1994), and analogous development of the opposite-sign layer has also been observed under leading-edge vortices on delta wings (Lin & Rockwell 1995;Visbal & Gordnier 1995;Shih & Ding 1996, 2002Ol & Gharib 2003). Given the conflicting observations on the presence and role of spanwise flow in leading-edge vortices discussed in § 1, and the observed entrainment of secondary vorticity illustrated in figure 2 it is plausible that annihilation of leading-edge vorticity due to the entrainment and interaction with this opposite-sign vorticity may provide a significant means of regulating leading-edge-vortex strength.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, at high angles of attack where translating wings and airfoils would normally stall, a leading-edge vortex has been observed at inboard spanwise positions (Ansari et al 2009;Carr, Chen & Ringuette 2012;DeVoria, Mahajan & Ringuette 2011;Lentink & Dickinson 2009a,b;Ozen & Rockwell 2012a). For a model fruit fly wing at Reynolds numbers between 100 and 14 000, Lentink & Dickinson (2009a,b) introduced a dimensionless framework in which they demonstrated that this behaviour is governed by centripetal and Coriolis accelerations due to wing rotation, which are inversely proportional to the Rossby number, interpreted as the wing aspect ratio.…”

Section: Introductionmentioning

confidence: 94%

“…Although the leading-edge vortex on a rotating blade has been described as attached at inboard spanwise positions, the precise definition of the term is yet lacking in the literature due to the complex and highly three-dimensional flow field that has been shown to exist on the surface of a rotating blade in recent years (Carr et al 2012;DeVoria et al 2011;Ozen & Rockwell 2012a;Garmann et al 2013b;Harbig, Sheridan & Thompson 2013). However, sufficiently close to the root, the vortex is typically well-defined and confined to the region over the suction surface of the blade, and thus we will refer to this state as attached.…”

Section: Introductionmentioning

confidence: 99%

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Vorticity transport in the leading-edge vortex on a rotating blade

2014

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Vorticity transport is analysed within the leading-edge vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the leading-edge vortex. An initial global analysis between the 25 and 50 % spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the leading-edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the 25 and 50 % spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the leading-edge vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of leading-edge-vortex circulation. Thus, it provides an important condition for maintenance of an attached leading-edge vortex on the inboard portion of the blade.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Vorticity transport in the leading-edge vortex on a rotating blade

2014

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“…Relevant studies include wings undergoing simultaneous rotation and pitching, and unsteady and steady rotation in the absence of pitching. Qualitative smoke, bubble or dye visualization has been employed by Ellington et al (1996), van den Berg & Ellington (1997), Willmott, Ellington & Thomas (1997), Thomas et al (2004), Lentink & Dickinson (2009) and DeVoria et al (2011). Sectional imaging involving either chordwise or spanwise planes, or a combination of them, has been used by Birch & Dickinson (2001), Birch, Dickson & Dickinson (2004), Ansari et al (2009), Jones, Ford & Babinsky (2011, Ozen & Rockwell (2012) and Wojcik & Buchholz (2012).…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional vortex structure on a rotating wing

Özen

Rockwell

2012

J. Fluid Mech.

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The three-dimensional structure of the leading-edge vortex on a rotating wing is addressed using a technique of particle image velocimetry. Organized patterns of chordwise-oriented vorticity, which exist within the vortex, arise from the spanwise flow along the surface of the wing, which can attain a velocity the same order as the velocity of the wing at its radius of gyration. These patterns are related to the strength (circulation) and coherence of the tip and root vortices. The associated distributions of spanwise-oriented vorticity along the leading-edge vortex are characterized in relation to the vorticity flux and downwash along the wing.

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“…57 The angle of attack was 45 • and trapezoidal and triangular velocity programs were studied. The flow structure is initially an overall vortex For each A, Carr et al 23,58 found that the primary flow structure early in the motion at this Re is again a loop-like vortex consisting of the LEV, TV, and TEV (the root vortex was outside the measurement volume).…”

Section: Introductionmentioning

confidence: 99%

Vortext Formation and Forces of Low-Aspect-Ratio, Rotating Flat-Plate Wings at Low Reynolds Number

Carr

Chen

Ringuette

2012

42nd AIAA Fluid Dynamics Conference and Exhibit

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We investigate experimentally the unsteady, three-dimensional flow structure and forces of rotating, flat-plate wings starting from rest, focusing on aspect ratio (A) effects. The wings are rectangular with A = 2 and 4 at 45 • angle of attack, the velocity program is trapezoidal with a total rotation of 120 • , and the tip Reynolds number is matched at 5,000. The experiments are done in a liquid-filled tank, and phase-locked, phase-averaged stereoscopic digital particle image velocimetry in finely-spaced chordwise planes is used to reconstruct the three-component volumetric velocity field. A submersible force transducer measures the lift. For each A the flow is initially a vortex loop containing the leading-edge vortex (LEV), tip vortex (TV), and trailing-edge vortex (TEV). The outboard LEV for A = 4 lifts off the plate and then breaks down, while the A = 2 flow remains more coherent for larger angles of rotation. Streamlines in the wing-fixed frame show that the A = 2 LEV is tilted aft with increasing span and contains both negative (inboard) and positive (outboard) spanwise velocity, w; the latter exists primarily behind the LEV due to its tilt. The TV is coherent and helical, and likely induces a significant downward flow and will be a region of low pressure. The A = 4 LEV is also tilted but contains only small, primarily positive spanwise velocity, and the TV is less coherent. In the lab-fixed frame, streamlines show that the A = 2 LEV has both positive and negative w, and a tilted, somewhat helical structure. Near the LEV core there is significant negative w and helical streamlines of an opposite sense. Initially the A = 4 LEV is conical (increasing in size with span) and locally two-dimensional. As LEV lift-off and breakdown occur, the diameter of the conical "outer" LEV streamline pattern increases substantially but still indicates bulk rotation. "Inner" streamlines show multiple LEVs, followed by a more complex breakdown structure. The streamline patterns agree well with the structures identified by the Q-criterion. Velocity vectors in a mid-span plane indicate increasingly downward-oriented velocity in the labfixed frame with time, which is stronger for A = 2. The lift coefficient for each case shows an initial peak during acceleration, to which added mass contributes significantly, followed by a local minimum where the lift coefficient for both As have approximately the same value. For both cases, the lift coefficient then rises until the point that deceleration begins.The rise, ∼54% for A = 2 and ∼20% for A = 4, is influenced by the spatio-temporal development of the loop structure for both cases, as well as the vortex breakdown and bulk rotation of the breakdown flow.

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Vortex Formation and Saturation for Low-Aspect-Ratio Rotating Flat Plates at Low Reynolds Number

Cited by 24 publications

References 57 publications

Vorticity transport in the leading-edge vortex on a rotating blade

Vorticity transport in the leading-edge vortex on a rotating blade

Three-dimensional vortex structure on a rotating wing

Vortext Formation and Forces of Low-Aspect-Ratio, Rotating Flat-Plate Wings at Low Reynolds Number

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