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Near-field tip vortex behind a swept wing model

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Abstract

The near-field flow structure of a tip vortex behind a sweptback and tapered NACA 0015 wing was investigated and compared with a rectangular wing at the same lift force and Re=1.81×105. The tangential velocity decreased with the downstream distance while increased with the airfoil incidence. The core radius was about 3% of the root chord c r, regardless of the downstream distance and α for α<8°. The core axial velocity was always wake-like. The core Γc and total Γo circulation of the tip vortex remained nearly constant up to x/c r=3.5 and had a Γco ratio of 0.63. The total circulation of the tip vortex accounted for only about 40% of the bound root circulation Γb. For a rectangular wing, the axial flow exhibited islands of wake- and jet-like velocity distributions with Γco=0.75 and Γob=0.70. For the sweptback and tapered wing tested, the inner region of the tip vortex flow exhibited a self-similar behavior for x/c r≥1.0. The lift force computed from the spanwise circulation distributions agreed well with the force-balance data. A large difference in the lift-induced drag was, however, observed between the wake integral method and the inviscid lifting-line theory.

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Abbreviations

AR:

Aspect ratio (b 2/S)

b :

(Semi-)wing span

c :

Chord of rectangular wing

c r :

Root chord

c t :

Tip chord

C D :

Drag coefficient without wing tip effects

C Di :

Lift-induced drag coefficient (D i /0.5ρu 2 S)

C D,3-D :

Drag coefficient of a 3-D wing configuration

C L :

Lift coefficient without wing tip effects (L/0.5ρu 2 S)

C L,3-D :

Lift coefficient of a 3-D wing configuration

D :

Drag without wing tip effects

D 3-D :

Drag of a 3-D wing configuration

D i :

Lift-induced drag

L :

Lift

p :

Local static pressure

p :

Free-stream static pressure

r :

Radial position

r o :

Vortex outer radius

r c :

Vortex core radius

Re :

Reynolds number (u c r/ν or u c/ν)

S :

Wing area

u :

Axial mean velocity

u c :

Core axial velocity

u :

Free-stream velocity

v :

Transverse mean velocity

v θ :

Tangential velocity

w :

Spanwise mean velocity

x :

Streamwise or axial direction

y :

Normal direction

z :

Spanwise direction

ρ:

Fluid density

ν:

Fluid kinematic viscosity

ζ:

Streamwise vorticity (∂w/∂y - ∂v/∂z)

Γ:

Circulation or vortex strength

Γb :

Bound root circulation

Γc :

Core circulation

Γo :

Total circulation

α:

Angle of attack

αss :

Static-stall angle

λ:

Taper ratio (c t/c r)

ψ:

Stream function

φ:

Velocity potential

σ:

A source term in Eq. 6 (∂v/∂y + ∂w/∂z)

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Acknowledgments

This work was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada.

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Correspondence to T. Lee.

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Gerontakos, P., Lee, T. Near-field tip vortex behind a swept wing model. Exp Fluids 40, 141–155 (2006). https://doi.org/10.1007/s00348-005-0056-y

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