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Research Papers: Fundamental Issues and Canonical Flows

Experimental Investigation of the Aerodynamics and Flowfield of a NACA 0015 Airfoil Over a Wavy Ground

[+] Author and Article Information
T. Lee, V. Tremblay-Dionne

Department of Mechanical Engineering,
McGill University,
Montreal, QC H3A 2K6, Canada

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 1, 2017; final manuscript received January 17, 2018; published online March 13, 2018. Assoc. Editor: Moran Wang.

J. Fluids Eng 140(7), 071202 (Mar 13, 2018) (10 pages) Paper No: FE-17-1555; doi: 10.1115/1.4039236 History: Received September 01, 2017; Revised January 17, 2018

The aerodynamic properties and flowfield of a NACA 0015 airfoil over a wavy ground were investigated experimentally via surface pressure and particle image velocimetry (PIV) measurements. Flat-surface results were also obtained to be served as a comparison. For the wavy ground, there exhibited a cyclic variation in the sectional lift coefficient Cl over an entire wavelength. The maximum Cl observed at the wave peak (produced by the wavy ground-induced RAM pressure) and minimum Cl occurred at the wave valley (resulting from the unusual suction pressure developed on the airfoil's lower surface due to the converging-diverging flow passage developed underneath it) reduced with increasing ground distance. By contrast, the pitching-moment coefficient showed an opposite trend to the variation in Cl and had an almost all-negative value. Meanwhile, two peak values in the drag coefficient over each wavelength were observed. The wavy ground effect-produced gains in the mean Cl and lift-to-drag ratio were at the expense of longitudinal stability. Additional measurements considering different wavelengths and amplitudes are needed to further quantify the impact of wavy ground on wing-in-ground effect (WIG) airfoils and wings.

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Figures

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Fig. 1

Schematics of airfoil model and ground surface and definition of ground distance h. (a) Wavy ground, ((b) and (c)) measurement position and phase angle along one wavelength, and (d) flat ground. x0′ to x5′ indicates trailing-edge moves toward the wave valley. x5′ to x10′ indicates trailing-edge moves toward the wave peak or away from the wave valley. AC denotes aerodynamic center.

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Fig. 2

Normalized mean axial flow developed over the wavy ground: (a) iso-u/U contour and (b) u/U velocity profiles

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Fig. 3

Cyclic variation in the aerodynamic coefficients of the NACA 0015 airfoil with the measurement position x′/λ over one wavelength at different h/c for α = 12 deg. BA denotes baseline airfoil. Dashed lines denote values over a flat ground.

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Fig. 4

Impact of wavy ground on Cp distribution as a function of x′/λ over one wavelength h/c = 5% for α = 12 deg

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Fig. 5

Iso-u/U contours around the NACA 0015 airfoil over the wavy ground at wave peak (x10′) and wave valley (x5′) at different h/c

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Fig. 6

Impact of flat ground effect on iso-u/U contour around the NACA 0015 airfoil as a function of h/c. (a) BA, (b) h/c = 5%, (c) h/c = 10%, (d) h/c = 20%, and (e) h/c = 40%. BA denotes baseline airfoil.

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Fig. 7

Ground effect on surface pressure coefficient distribution at different h/c and x′/λ at α = 12 deg. Wavy ground: (a) x′/λ = 0, (b) x′/λ = 0.4, and (c) x′/λ = 0.7. (d) Flat ground. BA denotes baseline airfoil.

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Fig. 8

u/U velocity profiles for h/c = 10%. (a) BA, (b) flat ground, (c) wavy ground at x′/λ = 1.0, and (d) wavy ground at x′/λ = 0.5.

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Fig. 9

Maximum (denoted by open symbols) and minimum (denoted by solid symbols) aerodynamic coefficients over one wavelength at different h/c. BA denotes baseline airfoil.

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Fig. 10

Ground effect on the variation of mean aerodynamic coefficients of the NACA 0015 airfoil with h/c. Solid lines denote wavy ground. Dashed lines denote flat ground. BA denotes baseline airfoil.

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