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Research Papers: Flows in Complex Systems

Effect of a Single Leading-Edge Protuberance on NACA 634-021 Airfoil Performance

[+] Author and Article Information
Chang Cai

State Key Laboratory of
Hydroscience and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: cai-c12@mails.tsinghua.edu.cn

Zhigang Zuo

State Key Laboratory of
Hydroscience and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: zhigang200@mail.tsinghua.edu.cn

Shuhong Liu

Mem. ASME
State Key Laboratory of
Hydroscience and Engineering,
Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: liushuhong@mail.tsinghua.edu.cn

Takao Maeda

Division of Mechanical Engineering,
Mie University,
Tsu, Mie 514-8507, Japan
e-mail: maeda@mach.mie-u.ac.jp

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 4, 2016; final manuscript received April 3, 2017; published online October 31, 2017. Assoc. Editor: Olivier Coutier-Delgosha.

J. Fluids Eng 140(2), 021108 (Oct 31, 2017) (7 pages) Paper No: FE-16-1494; doi: 10.1115/1.4037980 History: Received August 04, 2016; Revised April 03, 2017

Leading-edge protuberances on airfoils or wings have been considered as a viable passive control method for flow separation. In this paper, the aerodynamic performance of a modified airfoil with a single leading-edge protuberance was investigated and compared with the baseline NACA 634-021 airfoil. Spalart–Allmaras turbulence model was applied for the numerical simulation. Compared to the sharp decline of baseline lift coefficient, the stall angle of the modified foil decreased and the decline of the lift coefficient became mild. The poststall performance of the modified airfoil was improved, while the prestall performance was declined. Asymmetric flows along the spanwise direction were observed on the modified airfoil, and the local region around one shoulder of the protuberance suffered from leading-edge separation at prestall angles of attack, which may be responsible for the performance decline. At poststall angles of attack, the attached flows along the peak of the protuberance with a sideward velocity component would help improving the total performance of the airfoil. Experimental visualization methods, including surface tuft and smoke flow, were performed, and the asymmetric flow pattern past the protuberance was successfully captured. This specific phenomenon may be largely related to the formation of the biperiodic condition and other complicated flow patterns induced by multiple leading-edge protuberances. The formation mechanism and suppression method of the symmetry breaking phenomenon should be investigated more deeply in the future to guide the practical application of this passive control method.

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Figures

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Fig. 2

Detail of the leading-edge protuberance

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Fig. 3

Mesh distribution around the modified airfoil

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Fig. 4

Mesh independence test at α = 15 deg

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Fig. 5

Position of tufts on the suction surface of the modified airfoil

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Fig. 6

Test sections for smoke flow visualization

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Fig. 7

Aerodynamic force coefficient gained through numerical simulation compared to experimental data from Refs. [7] and [8]: (a) lift coefficient and (b) drag coefficient

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Fig. 8

Limiting streamlines and recirculation regions shown by isosurface of zero longitudinal velocity (left: baseline; right: modified): (a) 9 deg, (b) 15 deg, (c) 20 deg, and (d) 24 deg

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Fig. 9

Near-wall flow visualization (left: experimental tuft visualization; the dash line indicates the approximate separation line. Right: limiting streamlines by CFD): (a) 15 deg and (b) 24 deg.

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Fig. 10

Instantaneous image of smoke flow at section A: (a) 15 deg and (b) 24 deg

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Fig. 11

Averaged image of smoke flow (top) and 2D streamlines gained by numerical simulation (bottom) at α = 15 deg: (a) section A, (b) section B1, (c) section B2, and (d) section B3

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Fig. 12

Averaged image of smoke flow (top) and 2D streamlines gained by numerical simulation (bottom) at α = 24 deg: (a) section A, (b) section B1, (c) section B2, and (d) section B3

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Fig. 13

Development of nondimensional streamwise vorticity ωx∗ at α = 15 deg

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Fig. 14

Limiting streamlines and recirculation regions shown by isosurface of zero longitudinal velocity by different turbulence models (modified airfoil, α = 15 deg): (a) SST k–ω model and (b) transition SST model

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