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Research Papers: Flows in Complex Systems

Surface Pressures Developed on an Airfoil Undergoing Heaving and Pitching Motion

[+] Author and Article Information
T. Lee

Department of Mechanical Engineering,
McGill University,
Montreal, QC H3A 2K6, Canada
e-mail: tim.lee@mcgill.ca

Y. Y. Su

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 July 16, 2014; final manuscript received December 15, 2014; published online February 2, 2015. Assoc. Editor: Kwang-Yong Kim.

J. Fluids Eng 137(5), 051105 (May 01, 2015) (11 pages) Paper No: FE-14-1384; doi: 10.1115/1.4029443 History: Received July 16, 2014; Revised December 15, 2014; Online February 02, 2015

The surface pressure distributions and flow patterns developed on and around a NACA 0012 airfoil undergoing heaving and pitching were investigated at Re = 3.6 × 104. Despite extensive investigations conducted by researchers elsewhere, the surface pressure measurements are, however, not readily available in the open archives, which are of importance not only in understanding the unsteady-airfoil boundary-layer flow but also for computational fluid dynamics (CFD) validation. Nevertheless, the results show that the behavior of the surface pressure distribution and the flow pattern of pure heaving closely resembled those of pure pitching. For combined heaving and pitching, the critical aerodynamic values (such as dynamic Cl,max, peak negative Cm, Cl-hysteresis and torsional damping) always exhibited a maximum value at phase shift ϕ = 0 deg. More interestingly, the ϕ = 180 deg phase shift produced a virtually unchanged surface pressure distribution over an entire combined motion cycle.

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Figures

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Fig. 1

Experimental setup and airfoil model. (a) Schematics of airfoil heaving and pitching mechanism, (b) input and output signals of heaving and pitching, (c) heaving and pitching motion profiles at selected ϕ for αo = 10 deg and Δα = 6 deg, and (d) pressure orifice locations

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Fig. 2

Smoke-flow patterns for αo = 10 deg and Δα = 6 deg at selected α, t/T and ϕ. αu and αd denote angles during pitch-up and pitch-down, respectively

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Fig. 3

Smoke-flow patterns of the static airfoil at selected α: (a) α = 6 deg, (b) α = 8 deg, (c) α = 10 deg, (d) α = 12 deg, (e) α = 14 deg, and (f) α = 16 deg

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Fig. 4

Cp distributions of pure heaving, pure pitching, and combined motion with ϕ = 0 deg for αo = 10 deg and Δα = 6 deg. (a) t/T = 0.23, (b) t/T = 0.27, (c) t/T = 0.37, (d) t/T = 0.45, (e) t/T = 0.48, (f) t/T = 0.50, (g) t/T = 0.57, (h) t/T = 0.66, and (i) t/T = 0.75.

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Fig. 5

Dynamic-Cl and -Cm loops for pure heaving and pure pitching. Solid lines and symbols denote upstroke. Dashed lines and open symbols denote downstroke.

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Fig. 6

Spatial-temporal Cp representation for αo = 10 deg and Δα = 6 deg. (a) Pure heave αo = 10 deg, (b) pure pitch αo = 10 deg, Δα = 6 deg, (c) ϕ=0 deg, (d) ϕ=90 deg, (e) ϕ=180 deg, and (f) ϕ=270 deg.

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Fig. 7

Impact of ϕ on dynamic-Cl and Cm loops for αo = 10 deg, 8 deg and 5 deg with fixed Δα = 6 deg. Solid circles and stars denote start of upstroke and beginning of downstroke.

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Fig. 8

Cp distribution for αo = 10 deg and Δα = 6 deg with ϕ = 90 deg, 180 deg, and 270 deg. The pure pitch distributions are shifted by a phase equivalent to ϕ. ϕ=90 deg: (a) t/T = 0.27, (b) t/T = 0.37, (c) t/T = 0.50, (d) t/T = 0.66, and (e) t/T = 0.75; ϕ=180 deg (f) t/T = 0.27, (g) t/T = 0.37, (h) t/T = 0.50, (i) t/T = 0.66, and (j) t/T = 0.88; and ϕ=270 deg (k) t/T = 0.23, (l) t/T = 0.27, (m) t/T = 0.37, (n) t/T = 0.50, and (o) t/T = 0.66.

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Fig. 9

Impact of ϕ on critical aerodynamic values

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Fig. 10

Spatial-temporal Cp representation for αo = 5 deg and Δα = 6 deg. (a) Pure heave αo = 5 deg, (b) pure pitch αo = 5 deg, Δα = 6 deg, (c) ϕ=0 deg, (d) ϕ=90 deg, (e) ϕ=180 deg, and (f) ϕ=270 deg.

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